Overview of Energetics and
Homeostasis in Animals
Bioenergetics
Energy is often defined as capacity to
do work, but in living systems it is
best
defined
as
ability
to
cause
specific change. The different kinds of
changes made by cells and living things
or the use of energy by cells are
1.Changes
in
chemical
bonds(chemical work) as in biosynthesis
of new molecules for growth of new cells
which
requires
new
synthesis
of
molecules and maintenance of
existing
cells where large molecules easy to
damage and must be recycled as in the
formation of proteins, fats and other
organic compounds. In synthesis of large
molecules much energy
is required.
Cells need to change with time as it
needs certain proteins during interphase
as well as foods changes to be used by
the body
2. Changes in location (mechanical
work) Living things and cells undergo
movement, to move relative to something
else (e.g. flagellated cells sperm);
move
relative
to
environment
like
ciliated epithelium in bronchial tubes
move particles relative to cells; muscle
cells contract in one.
3. Changes in concentration across
membrane (concentration work) as in when
molecules or ions move against chemical
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concentration gradient (eg: cells must
pump amino acids into cell)
4. Changes in cell's electrical
potential (electrical work)
as energy
in electrochemicial gradient can be used
to make ATP in bacteria, chloroplasts &
mitochondria and ATP can be used to make
electrochemical
gradient
(membrane
potential) as in electric eel
5.
Changes
in
thermal
energy
(heat). In homeotherms like the birds
and
mammals,
relatively
constant
temperature must be maintained and heat
production is the major use of food
energy
6.
Changes
in
bioluminescence
("light" work) such as in fireflies,
some bacteria
The environmental energy available at
earth's surface is largely light light
energy. Many organisms capture light
energy most plants, some bacteria, some
protests are photosynthetic organisms
called
"phototrophs"
Phototrophs
are
organisms which use light energy to
make all molecules required for life
from inorganic precursors like CO2 and
H2O. Chemotrophs use chemical energy
stored in light (eg: starch) as energy
source during darkness; organisms get
energy from source other than light. All
animals, fungi, many protists, most
bacteria and a few parasitic plants are
chemotrophs. Energy is released from
chemicals they take up
from the
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environment in fermentation, glycolysis,
respiration and others sources too
Metabolic Rate is the
energy used
by organisms per unit time.
It is
measured in calories – amount of heat
energy --> raise 1g H2O 1oC
[14.5o to
o
15.5 C], linked to Krebs Cycle - MR is
determined by O2 consumption
often as
VO2max
where
the
minimal
calories
required for basic functions of life and
the maximal calories is on the peak of
metabolic activity
as in cases of
athletes in the Olympics . Metabolic
Rates is greatly influenced by several
variables
such as age,
sex,
body
size, temp, food levels, time of day,
size of organism, hormonal balance,
available
O2
The
basal metabolic rate (BMR) in
endotherms (animals that derive
body
heat from
own metabolism)
is when
they
at
rest
without
stress.
In
human males
1,600 - 1,800 Kc/d
and
females
is 1,300 - 1,500 Kc/d.
HOMEOSTASIS is how Animals regulate
their internal environment and maintain
a steady state internal environment
(constancy)
in face of a changing
external
environment.
Animals adjust to these changes.
Each stimuli the animal receives calls
for
corresponding
response.
Physiological Compensation is the short
Notes in Animal Physiology by CCDivina…………
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term
physiological
adjustments or
adaptations to environmental changes,
i.e.,
homeostatic
compensation
Internal "Milieu" as Claude Bernard
in 1880's referred to it is the internal
environment of the interstitial fluids
filling spaces between cells exchanging
nutrients
with
the
blood.
The
Constancy of Human milieu is
body
temperature of
37o C
+
1o C;
pH of
7.4
+
0.1 and
blood
sugar of
0.1%
[mg% - 100 mg/100ml
blood]
Homeostatic
Regulation
mechanisms that cells have
maintain constancy.
is the
evolved to
A Homeostatic Regulator mechanism
has 3 parts:
receptor
detects
a
change,
controller
processes
the
informa-tion and the
effector produces
the response.
Here
are
some
Notes in Animal Physiology by CCDivina…………
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examples of Homeostatic Regulation
1.
Temperature
:
the
hypothalmus regulates body temperature
via homeostatic
thermoregulation...
2.
pH regulation of the blood .
If the
pH 7.4 + 0.1 has a shift of
0.4 pH unit , it will mean death. For
example a crying baby blows off CO2 and
lowers
blood
acidity
(alkalosis)
and
person
with bleeding
stomach
ulcers
favors
acidosis.
Carbonic
anhydrase
converts
CO2
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+ H2O
<--->
H2CO3
<--->
H+ +
HCO3 . Hemoglobin of the red blood cells
pick up H+ ions and buffering blood.
Buffer is: a substance, as Hemoglobin
and other proteins that in solution
tends to stabilize the hydrogen-ion
concentration by neutralizing, within
limits, both acids and bases. If
pH
blood drops [H+ ^] then
HCO3
+
H+
shifts ---> to
H2CO3
and vice versa.
Calcium homeostasis.
In blood, the
normal range is 9
to 11 mg%. Ca+2 is needed for nerve
function,
muscle
contraction,
blood
clotting,
etc..
Calcium
regulation
functions via antagonistic hormones .
The
thyroid makes calcitonin hormone
that lowers Ca levels and causes Ca to
Notes in Animal Physiology by CCDivina…………
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be
deposited
into
bone
reduces
intestinal absorption of Ca and reduces
Ca uptake by kidney. The parathyroid -->
parathyroid hormone raises Ca levels,
stimulates release Ca from bone and
increases Ca uptake by intestine &
kidney
4. Blood Glucose balance . the
normal range of blood sugar is 80120mg/100ml. The pancreas makes insulin
and glucagon, which are antagonistic
hormones
water
5. Osmoregulation maintains the
balance of organism. Osmosis is
Notes in Animal Physiology by CCDivina…………
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the
net movement of water through a
semi-permeable membrane like the cell
membrane. Terrestrial animals gain water
from food & drink and lose water by
urinating, defecating, & evaporation.
Aquatic animals could be osmoconformer
(when the internal [solute] same as
environment) or osmoregulator when
internal
[solute]
maintain
constant
level.
Osmoregulation is a challenge to
both fresh water fish
and
seawater
fish . Freshwater fish has
greater
internal solutes thus constantly gains
water thru its body surface, its gills,
and food it eats. To compensates it does
not drink water and excretes large
amounts dilute urine and regains most
ions that are lost [Na, Cl, K] via food
& gills.
altwater fish
has less internal
solutes, thus constantly loses water. It
compensates by drinking saltwater, has
urine that is very concentrated. It
pumps ions [Na, Cl, K] out via gills
Notes in Animal Physiology by CCDivina…………
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Digestive System
Diets and feeding mechanisms
extensively among animals.
vary
All animals are heterotrophs and
must obtain their nutrients by consuming
organic molecules.
Animals
may
obtain
nutrient
by
suspension, substrate deposit, and fluid
or bulk feeding
Ingestion, digestion, absorption
elimination are the four main
stages of food processing.
and
Food processing in animals involves
ingestion,
digestion
(enzymatic
breakdown
of
the macromolecules of
food into their monomers) absorption
(the uptake of nutrient by body cells)
and
elimination
(the
passage
of
undigested materials out the body in
feces.
An adequate diet provides fuel, carbon
skeletons for biosynthesis and essential
nutrients. Carbohydrates and fats are
most often used as fuel. Monomer of
carbohydrates,
proteins,
fats
and
nucleic acids are used in biosynthesis.
Animals
store
excess
calories
as
glycogen in the liver and muscles and as
fat in adipose tissue. Undernourished
animals have diet deficient calories.
Notes in Animal Physiology by CCDivina…………
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Essential nutrients must be supplied
in pre-assembled form because of the
blood
lacks
the
machinery
for
biosynthesis; malnourished animals are
missing one or more of the essential
nutrients. Essential amino acids are
those
an
animal
cannot
make
from
nitrogen-containing precursor.
Animals can synthesis most essential
fatty acid. There are a few essential
unsaturated fatty acids.
Vitamins are organic molecules, many
of which serve as coenzymes or parts of
coenzymes; they are required in small
amount.
Vitamins, their functions,
symptoms and primary sources
VITAMINS
FUNCTION
Water Soluble Vitamins
B1
Formation
THIAMINE
of
coenzyme
in
Kreb’s
cycle
B2
Co-factor
RIBOFLAVIN
in
cellular
respiratio
n
B6
Co-enzyme
PYRIDOXINE
in
amino
and
fatty
acid
metabolism
B12
Nucleic
CYANOCOBALAMI
acid
N
synthesis,
prevents
pernicious
deficiency
DEFICIENCY
SYMPTOMS
PRIMARY
SOURCES
Beriberi,
neuritis,
heart failure
Organ
meats,
grains
Photophobia,
skin fissures
Milk eggs.
Liver,
whole
grains
Dermatitis
and
nervous
disorders
Whole
grains
Pernicious
anemia,
malformed red
blood cells
Organ
meats,
synthesized
by
intestinal
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anemia
BIOTIN
FOLIC ACID
NIACIN
PANTHO-THENIC
ACID
C
ASCORBIC ACID
FAT SOLUBLE
A
CAROTENE
D
CALCIFEROL
E
TOCOPHEROL
Protein
synthesis,
CO2
fixation,
amine
metabolism
Nucleic
acid
synthesis.
Red
blood
cells
formation
Coenzyme
in
hydrogen
transport
Forms part
of
coenzyme A
Vital
to
collagen
and ground
substances
Visual
pigment
formation,
maintains
epithelial
structure.
Increase
calcium
absorption
from
but,
bone
and
tooth
formation
Maintains
red
blood
cells
bacteria
Scaly
dermatitis,
muscle pains,
weakness
Egg white,
synthesized
by
digestive
flora
Anemia,
failure
of
red
blood
cells
to
mature
Meats
Pellagra,
skin lesions,
digestive
disturbances
Neuromotor
and
cardiovascula
r disorders
Scurvy,
failure
to
form
connective
tissues
Whole
grains
Most foods
Citrus
fruits
Nigh
blindness,
skin lesions
Egg yolk,
green and
yellow
vegetable
s
Rickets,
defective
formation
Fish
oils.
Liver
bone
Increased
fragility
of
red
blood
cells
Green
leafy
vegetable
s
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K
naphthaquinon
e
Stimulates
prothrombi
n
synthesis
by liver
Failure
of
blood-clotting
mechanism
Synthesis
by
intestina
l flora
Mineral
salt
are
inorganic
nutrients required by animals either as
macronutrients or micronutrients. The
essential macronutrients are potassium,
sodium, chlorine, phosphorus, calcium,
magnesium and sulfur. The micronutrients
are iron, copper, zinc and manganese.
Cobalt and iodine, valadium, selenium
are
required
trace
elements.
The
functions of the different minerals in
the animal’s organism are presented
below.
MINERALS
PRIMARY SOURCE
FUNCTION
ESSENTIAL MINERALS
Calcium
Component of bone and teeth, milk
and
essential for normal blood other dairy
clotting, needed for normal products,
muscle,
nerve
and
cell green leafy
function
vegetables
CHLORINE
Principal negative ion in Most
food,
interstitial
fluid, table salt
important in fluid balance
and in acid-base balance
MAGNESIUM
Component
of
many
co- Many foods
enzymes,
balance
between
magnesium and calcium ions
needed for normal muscle and
never function
PHOSPHORUS As
calcium
phosphate,
an All foods
important
structural
component of bone, essential
for
energy
transfer
and
storage, (component of ATP)
and
form
many
other
metabolic
processes,
component of DNA, RNA and
many proteins
POTASSIUM
Principal
positive
ion Many foods
within
cells,
influence
Notes in Animal Physiology by CCDivina…………
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SODIUM
SULFUR
muscle contraction and nerve
excitability
Principal positive ion in
interstitial
fluid,
important in fluid balance,
essential for conduction of
nerve impulses
Component of many protein,
essential
for
normal
metabolic activity
TRACE MINERALS
COBALT
Component of vitamin
B12,
essential
for
red
blood
cell
production
COPPER
Component
of
many
enzymes,
essential
for
melanin
and
hemoglobin syntheses
FLUORINE
Component of bone and
teeth
IODINE
Component
of
hormones
that
stimulate
metabolic
rate
IRON
MANGANESE
ZINC
Component
of
hemoglobin,
myoglobin, cytochrome
and
other
enzymes
essential to oxygen
transport
and
cellular respiration
Activates
many
enzymes,
essential
for urea formation
Component of enzymes,
peptidases important
in wound healing and
fertilization
Most foods,
table salt
Meat, fish,
legumes,
nuts
Meat,
products
dairy
Lever,
eggs,
fish,
wholewheat
flour,
beans
Some
natural
waters
Seafood,
iodized
salt,
Vegetables
grown
in
iodine-rich
soils
Meat specially
liver,
nuts,
egg
yolk,
legumes
Whole
grain
cereal,
egg
yolk,
green
vegetables
Shellfish,
meats, liver
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Mammalian digestive system
The mammalian digestive tract has a
four-layered wall over most of its
length; the smooth muscle layer propels
food along the tract by peristalsis and
regulates its passage through strategic
points by means of sphincters.
Mammals have accessory glands that
add digestive secretions to the tract
through ducts. These are the salivary
glands, pancreas and liver.
Digestion begins in the oral cavity,
whereas teeth -chew food into smaller
particles that are exposed to salivary
amylase.
Saliva
contains
buffers,
antibacterial
agents
and
mucin
for
lubricating the food.
The esophagus conducts food from the
pharynx other stomach by involuntary
peristaltic waves.
The stomach stores food and secretes
gastric juice which converts a mass to
acid
chyme,
gastric
juice
include
hydrochloric acids enzyme pepsin. Nerve
impulse
and
other
hormone
gastrin
regulate gastric motility and secretion.
Most digestion and virtually all
absorption occur in the small intestine,
the longest segment of the alimentary
canal
The pancreas and gallbladder, which
stores bile secreted by the liver, empty
ducts into the duodenum the first part
to
the
small
intestine,
Regulatory
hormones
such
as
secretin
and
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cholecystokinin regulates the activities
of the pancreas and gall bladder.
Digestive Tract and its Function
The
primary
function
of
the
alimentary tract is to provide body with
continual supply of water, electrolytes
and nutrients. To do so, food must be
moved along the alimentary tract at an
appropriate
rate
for
digestive
and
absorptive functions to take place.
The alimentary tract shows major
anatomical
differences
between
its
parts.
Each part is adapted for
specific functions such as
1. simple passage of food from one
point to another, as in esophagus
2. storage of food in the body of
the stomach or fecal matter in
the descending colon
3. digestion of food in the stomach,
duodenum, jejunum and ileum
4. absorption
of
digestive
endproducts in the entire small
intestines
and proximal half of
the colon
One of the most important features
of gastrointestinal tract is the myriad
of auto regulatory processes in the gut
that keeps the food moving at an
appropriate
paceslow
enough
for
digestion and absorption to provide the
nutrients needed by the body.
Characteristics of the Intestinal Wall
Notes in Animal Physiology by CCDivina…………
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A typical section of the intestinal
wall, showing layers from the outside to
inward
1.
the serosa
2.
a longitudinal muscle layer
3.
a circular muscle layer
4.
the submucosa
5.
the mucosa
In addition, a sparse layer of
smooth muscle fibers, the muscularis
mucosa lies in the deeper layers of
mucosa. The different layers of smooth
muscles perform the motor functions of
the gut.
Characteristic
Muscle
of
Intestinal
Smooth
1. The Functional Syncitium.
The individual smooth muscle fiber
lies close to each other. About 12
percent of the membrane surfaces are
actually
fused
with
membranes
of
adjacent muscle fibers in the form of a
nexus and most of the remainder of the
cell membranes of adjacent fibers lie in
extremely close opposite.
Measurements
of
ionic
transport
through these areas of close contact
demonstrate
extremely
low
electrical
resistance,
so
much
so
that
intracellular
electrical
current
can
travel very easily form one smooth
muscle fiber to another.
Therefore the
smooth muscle of the gastrointestinal
Notes in Animal Physiology by CCDivina…………
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tract performs as a functional syncitium
which
means
that
action
potentials
originating in one smooth muscle fiber
are generally propagated from fiber to
fiber.
2
Muscle
.
Contraction
of
Intestinal
The
Smooth
muscles
of
gastrointestinal
tract
exhibits
tonic and rhythmic contractions.
the
both
Tonic
contraction
is
continuous
lasting minute after minute or even hour
after
hour
sometime
increasing
or
decreasing in intensity but nevertheless
continuing. It is caused by a series of
action potential, the frequency of these
determine
the
degree
of
tonic
contraction. The intensity of tonic
contraction in each set of the gut
determines the steady pressure of the
segment, the tonic contraction of the
sphincters determines the amount of
resistance offered at the sphincter to
the movement of intestinal contents. In
this way, the pyloric the ileocecal and
the anal sphincters help to regulate
food movement in the gut.
The rhythmic contraction of the
gastrointestinal
smooth
muscles
is
responsible for the phasic function of
the gut, such a mixing of the food and
peristaltic propulsion of food.
Notes in Animal Physiology by CCDivina…………
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Innervations
Plexus
of
the
Gut
–
Intramural
The intramural plexus is especially
responsible for many neurogenic reflexes
that occur locally in the gut, such as
reflexes from the mucosal
epithelium
to increase the activity of the gut
muscle or to cause localize secretion of
digestive
juices
by
the
submucosal
glands. The plexus is also intimately
involved in coordination of the motor
movements of the gastrointestinal tract.
In
higher
forms
of
animals,
nutrition is ingestion, digestion and
assimilation and egestion. Ingestion is
acquiring the food from the environment.
Digestion is the physical and chemical
breakdown of food to be assimilated or
absorbed in circulation. Egestion is the
release of the undigested food.
Digestion needs the activities of
different digestive enzymes to break
them down chemically into absorbable
forms. In man, digestion takes place
along the digestive or alimentary tract,
the organs involved in digestion are the
mouth, the pharynx, esophagus, stomach,
small intestines and large intestines.
The digestive accessory glands are the
salivary gland, liver and pancreas.
Digestion takes place right after
ingestion. In the mouth, the food is
chewed
or
masticated
into
smaller
Notes in Animal Physiology by CCDivina…………
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particles to expose more surface area
for the action of the enzymes. The teeth
are
of
different
kinds,
like
the
incisors for biting, the canines for
tearing, the molars for grinding and
crushing.
The
tongue
mixes
the
masticated food with the saliva secreted
by the salivary gland. Saliva contains
water, mucin and ptyalin, an enzyme that
breaks
down
carbohydrates
into
disaccharides. When food is thoroughly
chewed it proceeds to the pharynx and
esophagus by swallowing or deglutition.
The food forms a bolus and moves along
the
tract
through
the
wave-like
contraction of muscles in the walls,
this
contraction
is
known
as
peristalsis.
The stomach is a large sac-like
organ that is closed at its upper part
by the cardiac sphincters and the lower
part of they pyloric sphincter. The
stomach stores the temporary partially
digested food. The glands of the stomach
wall
produces
gastric
juice
that
contains hydrochloric acid (HCl) and
pepsin.
Pepsin breaks down proteins into
polypeptides. The food is in a semiliquid chyme form when it leaves the
stomach
to
proceed
to
the
small
intestines.
The
small
intestines
are
approximately 22 meters long and have
three sections– the duodenum, jejunum
Notes in Animal Physiology by CCDivina…………
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and
ileum.
Final
digestion
and
absorption takes place in this stretch
of organ. Secretory gland cells of the
intestinal
walls
and
the
pancreas
secrete enzymes that finally breaks down
disaccharides
into
monosaccharides,
lipids into fatty acids and glycerol,
polypeptides
into
amino
acids
and
nucleic acids into nucleotides.
Liver
and
pancreas
facilitate
digestion in the small intestines. Liver
secretes
bile,
a
substance
that
emulsifies
fats
and
aid
in
its
digestion. Pancreas secrete pancreatic
juice containing a lot of digestive
enzymes that function in the small
intestines.
The
secretions
of
the
small
intestine
include
amylase
maltase,
sucrase,
lactase,
etc.
to
digest
carbohydrates and lipase to digest fats.
Several other associated organs secrete
chemicals into the small intestine to
aid in digestion: the pancreas secretes
enzymes like trypsin, chymotrypsin, and
alkali solutions like bicarbonate as
buffers and the liver and gall bladder
make and secrete bile. Bile contains no
enzymes, but salts to emulsify fat so it
can be digested.
Absorption of completely digested
food takes place in the ileum of the
small intestines. The villi or the small
fingerlike projections of the small
Notes in Animal Physiology by CCDivina…………
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intestines
increase
the
capacity of this organ.
absorption
The undigested food goes to the
large intestines or colon. Water from
the undigested particles is reabsorbed.
Note that no digestion takes place in
this
organ.
Storage
in
the
large
intestines lasts 12 to 1 hours before
harmless bacterial grow abundantly.
The large intestine or colon, which
begins with a blind pouch called the
cecum. In humans, this terminates in the
appendix, a finger-like extension which
may function in the immune system. The
large intestine functions to re-absorb
(resorb)
water
and
in
the
further
absorption of nutrients. The bacterial
flora of the large intestine includes
such
things
as
Escherichia
coli,
Acidophilus spp., and other bacteria, as
well as Candida yeast (a fungus). These
bacteria produce methane (CH4), hydrogen
sulfide (H2S), and other gases as they
ferment their food. Occasionally, some
of this gas is released as flatus. As
these bacteria digest/ferment left-over
food, they secrete beneficial chemicals
such as vitamin K, biotin (a B vitamin),
and some amino acids, and are our main
source of some of these nutrients.
Notes in Animal Physiology by CCDivina…………
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The rectum is the terminal portion
of the large intestine and functions for
storage of the feces, the wastes of the
digestive
tract,
until
these
are
eliminated. The external opening at the
end of the rectum is called the anus.
The
anus
has
two
sphincters,
one
voluntary
and
one
involuntary.
The
pressure of the feces on the involuntary
sphincter causes the urge to defecate
and the voluntary sphincter controls
whether a person defecates or not.
Functional Types of Movements
Gastrointestinal Tract
There
movements
tract
in
the
are
two
basic
types
of
occur
the
gastrointestinal
Notes in Animal Physiology by CCDivina…………
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1. Mixing movements, which keep the
intestinal
contents
thoroughly
mixed at all times.
2. Propulsive movements, cause food to
move forward along the tract at an
appropriate rate for digestion an
absorption
The Mixing Movement is caused by
local contraction of small segments of
the gut wall. These
movements
are
modified in different parts of the
gastrointestinal
tract
for
proper
performance.
The propulsive movements in the gut
are peristaltic. A contractile ring
appears around the gut and then moves
forward.
Peristalsis is an inherent property
of
any
synctial
smooth
muscle
but
stimulation
at
any
point
causes
a
contractile ring to spread in both
directions. Thus, peristalsis occurs in
gastrointestinal tract, the bile ducts,
other glandular ducts through the body,
the ureters and most major smooth muscle
tubes of the body.
Major Functions of the Stomach
1. Storage of large quantities of
food until it can be accommodated
in the lower portion of the
gastrointestinal tract
Notes in Animal Physiology by CCDivina…………
24
2. Mixing of this food with gastric
secretion until it forms a semi
fluid mixture called chime
3. Slow emptying of the food from the
stomach into small intestines at a
rate suitable for proper digestion
and
absorption
by
the
small
intestine.
Physiologically,
the
stomach can be divided into corpus
and antrum.
Storage Function of the Stomach
As food enters the stomach, it
forms concentric circles in the boy of
the stomach, the newest food lying close
to the esophageal opening and the oldest
food lying nears the wall of the
stomach. The stomach has relatively
little tone in its muscular wall so that
it
can
bulge
progressively
toward,
thereby
accommodating
greater
and
greater quantities of food up to a limit
of about 1 liter.
Mixing in the Stomach
The digestive juice of the stomach
is secrete by the gastric glands, which
cover almost the entire outer wall of
the
body
of
the
stomach.
These
secretions come immediately into contact
with the stored food lying against the
mucosal surface of the stomach. When the
stomach is filled, weak constrictor
waves, also called mixing wave moves
along the stomach wall approximately
once every 20 seconds. These waves move
Notes in Animal Physiology by CCDivina…………
25
the gastric secretions in the outermost
layer of food gradually toward the
antral part of the stomach. On entering
the
antrum,
the
waves
become
even
stronger
and
the
food
and
gastric
secretions also become mixed to greater
and greater degree of fluidity.
Peristalsis
also
contributes
to
mixing. Each time a peristaltic wave
passes over the antrum towards the
pylorus,
it
digs
deeply
into
the
contents of the antrum. The opening of
the pylorus is small enough the only a
few milliliters of antral contents are
expelled
into
duodenum
with
each
peristaltic wave, In backward though the
peristaltic ring the moving peristaltic
constrictive ring, combines with this
reflux
actions,
in
an
exceedingly
important
mixing
mechanism
of
the
stomach.
Chyme. After the food has become
mixed with the stomach secretion the
resulting mixture that passes down the
gut is called chyme. The degree of
fluidity
of
chyme
depends
on
the
relative amounts of food and stomach
secretion and on the degree of digestion
that has occurred. The appearance of
chyme is that of a murky, milky semi
fluid paste
Propulsion of Food Through the Stomach.
Notes in Animal Physiology by CCDivina…………
26
Strong
peristaltic
waves
occur
about 20 percent of the time in waves,
like the mixing waves, occurs about once
every 20 seconds.
As the stomach
becomes progressively more and
more
empty, these intense waves begin farther
and farther up the body of the stomach
gradually pinching of the lowermost
proteins of stored food, adding his food
to the chyme in the antrum.
The peristaltic waves often exert
as much as 50 to 70 cm of water
pressure, which is about six times as
powerful as the usual mixing waves.
Emptying the stomach. Emptying the
stomach is promoted by peristaltic waves
in the antrum of the stomach and
resistance of the pylorus to the passage
of food opposed it.
The pylorus
normally
remains
almost
but
not
completely closed because of mild tonic
contraction. The rate of emptying of
stomach is determined principally by the
degree
of
activity
of
the
antral
peristaltic waves.
The
degree
of
activity
of
he
pyloric pump is regulated mainly by
signals from the duodenum that depress
pyloric pump activity. In general when
excesses of volume of chyme or excess of
certain types of chyme have entered the
duodenum,
strong
negative
feedback
signals both nervous and hormones,
and
transmitted to the stomach to depress
Notes in Animal Physiology by CCDivina…………
27
the pyloric pump. Thus the mechanism
allows chyme to enter the duodenum only
as rapidly as it can be processed by the
small intestines.
Strong
nervous
signals
are
transmitted from the duodenum back to
the stomach when the stomach emptied
food into the duodenum. These signals
probably play the most important role of
all in deterring the degree of activity
of the pyloric pup and therefore, also
in determining the rate of emptying of
the stomach.
The
enterogastiric
reflex
is
especially sensitive to the presence of
irritant and acids in the duodenal
chyme. For instance, any time the pH f
the chyme in the duodenum
falls below
approximately 3.5 to 4, the enterogastic
reflex is immediately elicited, which
inhibits the pyloric pump and reduces or
even blocks further the reflex acidic
stomach contents in the duodenum until
the duodenal chyme can be neutralized by
pancreatic and other secretions
Breakdown of
also elicit this
rate of stomach
time is insured
digestion in the
small intestines.
protein digestion will
reflex by slowing the
emptying, sufficient
for adequate protein
upper portion of the
When fatty foods, especially fatty
acids, are present in the chyme that
Notes in Animal Physiology by CCDivina…………
28
enters the duodenum, the activity of the
pyloric pump is depressed and stomach
emptying is correspondingly slowed. This
plays an important role in allowing slow
digestion
of
the
fats
before
they
proceed into the deeper accesses of the
intestine.
Emptying
of
the
stomach
is
controlled to a moderate degree by
stomach factors such as the degree of
filling in the stomach and the activity
of the stomach peristalsis.
Probably,
the
more
important
control of stomach emptying, besides the
feedback
signal
from
the
duodenum,
include
especially
the
enterogastric
reflex and at a lesser extent hormonal
feedback. These two feedback signals
work to slow down the rate of emptying
when too much chyme is at the small
intestine, or the chyme is excessively
acidic, or there’s too much protein, or
if it is hypotonic or hypertonic, or
there is irritation.
In this way, the rate of stomach
emptying is limited to the amount of
chyme that the small intestines can
process.
Summary of Control Mechanism
1. Both
nervous
and
hormonal
input
regulate the activity of the GI tract.
Notes in Animal Physiology by CCDivina…………
29
The
nervous
mechanisms
control
appetite
and
peristalsis,
and
the
hormonal
factors
consist
of
three
hormones secreted by tissues of the GI
tract. These regulate gastric secretion
and motility, pancreatic secretion, and
gallbladder contraction.
One example of nervous control of
the GI tract is the swallowing reflex.
When food reaches the back of the
mouth, pressure sensitive nerve cells
send nerve impulses to the medulla of
the brain. The medulla coordinates a
series of 25 muscles in the throat and
esophagus which force the food toward
the stomach in an automatic wave of
contraction.
The entire wave requires nine to ten
seconds to complete, and is so well
coordinated that one can swallow while
upside down. The glottis is a muscular
structure at the top of the trachea that
closes during swallowing to prevent food
from
entering
the
lungs,
and
two
sphincters
open
and
close
during
contraction to keep food in the stomach.
2. The second nervous control is the
coordination
of
smooth
muscle
contractions that produce peristalsis in
the GI tract. This includes external
nerve input from the autonomic nervous
system, and internal control of the
tract by a nerve plexus within the tract
tissue.
External
nerves
also
exert
Notes in Animal Physiology by CCDivina…………
30
control over the function of related
glands such as the pancreas and salivary
glands.
Autonomic
Control
Gastrointestinal Tract.
of
the
The gastrointestinal tract receives
extensive
parasympathetic
and
sympathetic
innervations
that
are
capable of altering the overall activity
of the entire gut or of the specific
parts of it, particularly of its upper
end down to the stomach and its distal
end from the mid-colon region to the
anus.
Parasympathetic Innervations.
The parasympathetic supply to the
gut is divided into cranial and sacral
division, it causes general increase in
activity of the mesenteric plexus which
excites the gut wall and facilitates
most of the intrinsic excitatory nervous
reflexes of the gastrointestinal tract.
Sympathetic
Innervations.
Stimulation of the sympathetic nervous
system
inhibits
activity
in
the
gastrointestinal tract causing effects
essentially opposite to those of the
parasympathetic
system.
Thus,
strong
stimulation of the sympathetic system
can totally block movement of the food
through the gastrointestinal tract.
Notes in Animal Physiology by CCDivina…………
31
Application
1. GASTRITIS.
Most of us occasionally suffer from
gastritis (inflammation of the stomach
lining) with the familiar symptoms of
stomachache and "heartburn." The pain is
caused when food remains for too long a
period
in
the
stomach
and
excess
hydrochloric acid is secreted.
Heartburn has nothing to do with
the heart, but instead refers to the
pain that is produced when some of the
acidic material enters the lower end of
the esophagus and irritates esophageal
tissues. These conditions can occur when
one is under stress, or has eaten too
much, since both cause decreased gastric
motility.
The usual treatment for gastritis
is to swallow a buffering compound
(antacid) such as sodium bicarbonate,
which buffers the acid in the upper part
of the stomach and thereby relieves the
pain. Since not everyone should take
bicarbonate, due to its high sodium
content, a number of commercial antacids
have been developed that contain more
complex mixtures of buffering compounds.
2.
ACHYLIA
Occasion
the
stomach
has
the
opposite disorder in which insufficient
hydrochloric acid is secreted. This
condition is called achylia and is
estimated to occur in about 10% of the
population. The symptoms are usually
Notes in Animal Physiology by CCDivina…………
32
mild,
and
arise
from
too
rapid
evacuation
of
the
stomach
so
that
digestion is poor. The usual treatment
is
to
acidify
the
stomach
by
hydrochloric or glutamic acid taken with
meals.
3. ULCER
In a few people, gastrointestinal
disorders can become chronic, and the
stomach or duodenum becomes locally
inflamed and finally produces a craterlike sore called an ulcer.
In
rare
instances,
the
ulcer
becomes so large that it hemorrhages or
even perforates the stomach lining so
that
stomach
contents
enter
the
abdominal
cavity.
This
condition
represents
a
medical
emergency
and
requires immediate surgery and hospital
care.
For simple ulcers, the treatment
involves
a
diet
of
bland,
readily
digestible
foods,
and
avoidance
of
stressful situations. In more serious
ulcers that do not respond to dietary
changes, a drug called cimetidine is
useful. This compound works by blocking
the histamine response of gastric tissue
that would otherwise trigger a more
widespread inflammation and increased
gastric secretion. In about 75% of
patients treated with cimetidine, relief
of ulcer pain occurs in a few days and
the ulcer is healed in four to six
weeks.
Notes in Animal Physiology by CCDivina…………
33
4.
DIARRHEA
There are several common conditions
of the GI tract associated intestinal
motility. In diarrhea, the intestine
responds to inflammation by constant
peristalsis.
The inflammation can arise either
through some toxic substance in the
diet, as in food poisoning, or by viral
or bacterial infection of the intestinal
tissues. As a result food moves through
the tract far to~ rapidly. The feces are
fluid because the large intestine does
not have a chance to remove water.
Usually diarrhea is self-limiting
but in some circumstances it can be
seriously debilitating. For instance,
the diarrhea associated with cholera can
produce death through dehydration and
loss of salt from the body. Drugs are
available
that
control
diarrhea
by
reducing intestinal motility.
5. APPETITE REGULATION
Appetite
is
regulated
by
the
central nervous system, and is probably
related to nutrient levels circulating
in the blood, such as glucose and lipid.
The
receptors
are
in
the
hypothalamus of the brain, such that the
sensation of hunger is activated when
nutrient levels are relatively low.
Other
factors,
not
yet
completely
understood,
also
control
to
the
regulation of appetite and food intake.
Notes in Animal Physiology by CCDivina…………
34
6.
STOMACH CONTROL ON RATE OF DIGESTION
The
activity
of
the
stomach
controls the rate at which food is
presented
to
the
intestine
for
digestion, although some digestion of
occurs in the stomach as well. Hormones
exert both stimulating and inhibiting
effects on gastric juice. When food
reaches the stomach, gastrin is secreted
by cells in the terminal portion of the
stomach and travels via the blood stream
to the rest of the stomach, where it
stimulates motility and secretion of
gastric juice. The motility, in the form
of peristaltic contractions, squeezes
small quantities of food into the upper
intestine.
7.
CHOLECYSTOKININ AND SECRETIN
When food from the stomach reaches
the upper intestinal segment called the
duodenum, other cells of the intestine
secrete
cholecystokinin
(CCK)
and
secretin.
Amino acids and fatty acids in the
food
activate
CCK
release,
which
stimulates the gall bladder to contract
and
inject
bile
into
the
small
intestines. Stomach acid activates the
release of secretin, which in turn
travels to the pancreas by way of the
blood
to
stimulate
secretion
of
pancreatic juice.
Notes in Animal Physiology by CCDivina…………
35
Both CCK and secretin tend to
inhibit gastric activity. Thus if a meal
is high in fat and protein, it requires
a longer time to digest. The amino acid
and fatty adds cause a relatively large
amount of CCK to be secreted so that
gastric activity is slowed and thereby
increasing digestion time. Similarly,
higher stomach acid content in the food
reaching the intestine causes grater
release of pancreatic juice, the juice
contains bicarbonate, which acts as
buffer to neutralize stomach acid.
8. UNUSUAL FOOD ARE UNDIGESTED
Uptake of digested nutrients is
controlled by carrier enzymes in the
cell
membranes
of
the
intestinal
epithelial
tissue.
Each
enzyme
is
specialized
to
deal
with
specific
nutrient which can be used by the body
therefore unusual substances in the diet
tend not be absorbed, but instead are
passed into fecal materials
Other abnormalities associated with the
digestive system are:
1. Belching
is when swallowed gas
moves up the esophagus and is
released from the mouth and/or nose
2. Vomiting is an important reflex to
protect from harmful substances.
Illnesses like flu, extreme pain
(anywhere in the body: migraine,
kidney stones. . .), and other
stressful conditions can trigger
Notes in Animal Physiology by CCDivina…………
36
the
emptying
of
the
stomach
contents.
3. Hiatal hernia is caused in part by
failure of the cardiac sphincter to
close
properly
allowing
stomach
acid
to
enter
and
burn
the
esophagus.
4. An
ulcer
is
when
the
gastric
secretions
eat
through
stomach
(gastric ulcer) or intestinal wall
(duodenal ulcer).
5. Diarrhea
is having very loose,
watery feces and constipation is
having larger, harder, nearly dry
feces. Getting enough fiber is
importance
to
proper
intestinal
functioning because it holds water
in the feces. If feces are too dry
and hard, they will pass through
the
digestive
tract
with
difficulty,
possibly
leading
to
diverticulosis or diverticulitis.
Also, due to the increased transit
time,
there
is
more
time
for
bacteria to ferment the left-overs
and secrete increased amounts of
carcinogenic
byproducts,
thereby
increasing the person’s chances of
colon cancer.
Questions and Answers

What
determines
the
nutrients of an animal?
The diet
must
include
of
a
each type
specific
essential
of animal
group
of
Notes in Animal Physiology by CCDivina…………
37
essential
nutrients-essential
amino
acids, essential fatty acids, vitamins
and minerals – to provide the raw
materials
needed
to
synthesize
the
different kinds of organic molecules the
animal must have to sustain life. The
essential nutrient materials the animal
must have but cannot synthesize in its
cells. The nutrients that are essential
differ for each type of animal because
the ability to synthesize particular
molecules is a genetic trait acquired
through natural selection and because
each type of animal has a unique
evolutionary history.
In general, the more simple and
primitive animals are able to synthesize
more of the materials they require than
can
the
more
complex
and
advanced
animals. The ability to construct many
materials was lost during the evolution
of more complex animals because the
materials became so commonly available
in the diet, that the enzymes required
to
synthesize
them
were
no
longer
necessary and were lost from the genetic
repertoire.
For
example,
most
vertebrate
animals are able to synthesize vitamin C
in their cells, but this ability has
been lost in guinea pigs, fruit-eating
bats, a few types of bird, and some
other primates. All animals require
vitamin C for it is essential in the
construction
and
maintenance
of
substances that bind cells together,
especially in skin, bone and muscle. The
Notes in Animal Physiology by CCDivina…………
38
only animals that require vitamin in
their diets, however, are those with
ancestors that regularly consumed an
adequate
supply
of
vitamin
c
and
gradually lost the enzyme necessary for
its synthesis.

Why
do
malnourished
children
usually have enlarged abdomens?
A swollen abdomen and leg are
symptomatic
of
severe
protein,
deficiency, In such cases, the blood
does not contain enough plasma proteins
to hold water in the blood vessels and
water seeps out of the capillaries and
accumulates in the interstitial fluids
between
cells,
especially
in
the
abdominal
cavity
and
legs.
This
conditions
also
produces
low
blood
pressure
and
cause
the
problems
associated with poor blood circulation.
In parts of Africa a child with an
enlarged
abdomens
is
said
to
kwashiorkor, which means “ the rejected
one, because protein deficiency begins
when a child is weaned after a younger
sibling is born, without the proteinrich milk from its mother, a child in a
poverty-stricken
area
is
likely
to
suffer
form
an
inadequate
protein
intake.
Notes in Animal Physiology by CCDivina…………
39

What
is
the
advantage
of
a
digestive tract as compared with
digestive cavity?
A digestive cavity or incomplete
digestive system has only one opening to
the outside environment. A digestive
tract or complete digestive system has
tow openings, one for food intake and
the other for waste removal. Cnidarians,
flatworms and other acoelomates have
digestive cavities 9 the gastrovacular
cavity) Advanced animals including both
pseudocoelomates and coelenterates, have
digestive tracts.
Food enters a digestive cavity by
way of the single opeing, whichis ofhten
ringed with special structures to poison
the prey and so keep it form stuggling
and injuring tissue inside the cavity.
The food then moves into the cavity,
where it is digested, the portions of
food that cannot be digested are moved
out of the body through the cavity,
where it is digested. The portions of
food that cannot be digested are moved
out of the body through the same opening
in the form of feces. Because the
digestive cavity has a single opening,
food entering the cavity cannot be
separated form the feces leaving the
cavity. To prevent food and feces from
mixing food is not taken in at the same
time the feces leave- a restriction that
limits the rate of food intake.
A digestive tract founding most
animals, is a muscular tube with tow
Notes in Animal Physiology by CCDivina…………
40
openings, one for food intake, the mouth
and the other for feces removal (the
anus) the one way system permits food to
be
ingested
and
held
which
fecal
material is collected and expelled at
the same time. The one-way flow also
enables each segment of the tract to be
specialized for performing a particular
function o food passes through a sort of
assembly line form mouth to anus. The
degree of this specialization is greater
in the vertebrate digestive tract, which
consist of specific region of different
functional initial preparation of food,
storage,
digestion,
absorption
and
formation and removal of feces. Each
region is separate form the other by
special
circular
muscle,
called
sphincters, that can contract to close
off the region of the tract.

How do the digestive
carnivores differ from
herbivores?
tract
those
of
of
Animal meat requires more storage
and
less
processing
than
plant
materials. The teeth of a carnivore are
pointed and sharp for killing it preys
and tearing it into pieces small enough
to
swallow.
Animal
meat
does
not
requires
chewing.
The
teeth
of
a
herbivore, by contrast are flat for
crushing and grinding plant materials. S
mammal cannot digest cellulose and so
derives
not
nutrient
from
plant
materials unless chewing ruptures the
Notes in Animal Physiology by CCDivina…………
41
cells walls. A carnivore has a large
stomach for food storage, since it
reacts large and infrequent meals. The
stomach of dog or cat makes up 70% of
its digestive tract. An herbivore has
smaller stomach because it eats smaller
amount of food more frequently. The
stomach of a horse makes up only about
8% of its digestive tract (a ruminant
however, has an enormous stomach with
several
chambers,
for
digestion
f
cellulose by bacterial and protozoa.
Most digestion and all absorption food
take place in the small intestines and a
carnivore,
whose
for
requires
less
processing,
has
a
shorter
small
intestine than an herbivore, whose food
requires extensive processing.

What prevent the
digestive
tract
digested?
walls
from
of
the
being
Both
the
stomach
and
small
intestine
contain
enzymes
that
can
digest their own muscular walls. Yet
this rarely happens, because the protein
–digesting enzymes are not active until
released into the lumen of the stomach
or small intestine and the inner walls
of these structures are covered with a
protective coat of mucus.
Digestive glands in glands in the
pancreas
and
walls
of
the
stomach
secrete
proteolytic
enzymes
(pepsin,
trypsin,
and
chymotrypsin)
as
an
inactive
enzyme
precursors,
known
Notes in Animal Physiology by CCDivina…………
42
generally as zymogens, the enzyme do not
become active until they reach the lumen
of the stomach or small intestine, thus,
protein digestion does not occur in the
glands, ducts or walls of the digestive
system.
Active protein-digesting enzymes in
the lumen of the digestive tract cannot
digest the walls of the tract, because
the walls are lined with a protective
film of mucus that cannot be digested by
enzymes.
Occasionally,
however
the
protective layer of mucus breaks lose
and the walls of the stomach or small
intestine are digested, two materials
known to remove much are alcohol and
aspirin, Emotional stress also leads to
ulcers, usually duodenal ulcers, when
the acidic gastric juicers are not
immediately neutralized by bicarbonates
as the juices enter the duodenum.

Why do cows have so many stomachs?
A cow has four stomach, rumen,
reticulum, omasum and abomasum. The
first three stomachs are pouches derived
form the esophagus, and the abomasun is
the
true
stomach.
This
unusual
arrangement of the mammalian digestive
tract found, only in ruminants, cudchewing hoofed mammals such as cows,
sheep and deer is an adaptation for
digesting the cellulose within plant
cells. Cellulose is a polymer of glucose
and an excellent source of energy. No
mammal is able to synthesize an enzyme
Notes in Animal Physiology by CCDivina…………
43
that digest cellulose, but ruminants
digest
it
by
harboring
cellulosedigesting bacteria and protozoa within
their stomachs.
The
cellulose
digesting
microorganisms live in the rumen and
reticulum of a cow, Swallowed food
enters firs the rumen and then the
reticulum where the microbes digest and
ferment the liberated glucose, since
condtions
inside
the
stomachs
are
anaerobic,
from
the
reticulum,
the
coarse plant materials are regurgitated
or rechewed and then swallowed again for
further
enzymatic
action.
These
microorganisms use the producers of
their digestion and release fatty acids,
which move to the omasum, along with
some of the bacteria and protozoa. There
the
material
is
concentrated
by
reabsorption of water through the omasum
walls
and
then
is
moved
to
the
abomassum,
where
acids
kill
the
microbes, in the small intestines, the
microbes are digested and their amino
acids,
glucose
and
other
monomers,
together
with
fatty
acids
released
earlier, are absorbed into the blood
stream of the cow. The four stomachs of
the
ruminant
enable
part
of
the
digestive tract to be more specialized
than the digestive tracts of other
herbivores of ridding of cellulose, for
absorption and recycle of water from the
quantity of saliva use kind digestion by
the microorganisms, and for killing of
he microorganisms by acids.
Notes in Animal Physiology by CCDivina…………
44

Why do we have appendix?
An appendix is found only in
humans, a few species of great apes and
the wombat (a marsupisal). About 6 cm
long and 1 cm in diameter, it is a
hollow organ that dangles from the
cecum,. The walls of the appendix are
muscular and line first with a layer of
lymph tissue, and then an innermost
layer of epithelium It is structurally
similar to the colon and is also capable
of peristalsis. The appendix has no
known function; we don not know why
humans
have
one.
Since
it
vaguely
resembles a lymph node, the appendix may
function
to
prevent
intestinal
infections
Appendix or inflammation of the
appendix is the most common cause of
emergency surgery today, the appendix
becomes a liability when its lumen
becomes blocked by fecal material or by
swelling of the lymph tissue in reaction
to an infection. Fluids secreted by the
appendix then accumulate and become
infected by intestinal bacteria, the
areas then become inflamed, swollen and
painful. If not removed, the appendix
may
burst
and
spread
infection
throughout the abdominal cavity.
Notes in Animal Physiology by CCDivina…………
45
RESPIRATORY SYSTEM
The
respiratory
system
supplies
oxygen to the tissues and removes carbon
dioxide The major functional events of
respiration
include
pulmonary
ventilation, diffusion of oxygen and
carbon dioxide between the blood and
alveoli, transport of oxygen and carbon
dioxide to and from the peripheral
tissues, and regulation of respiration.
Pulmonary Ventilation
Lung volume increases and decreases
as the thoracic cavity expands and
contracts. The lung is held to the
thoracic wall as if glued, except that
they can slide freely in the thoracic
cavity. Any time the length or thickness
of the thoracic cavity increases or
decreases, simultaneous changes in lung
volume occur. The lungs can be expanded
and contracted into ways (1) by downward
and upward movement of the diaphragm to
lengthen or shorten the chest cavity and
(2) by elevation and depression of the
ribs to increases and decrease the
antero-posterior diameter of the chest
cavity.
Raising and lowering the rib cage
cause the lungs to expand and contract.
In the natural resting position, the
ribs
slant
downward,
allowing
the
sternum to fall backward towards the
vertebral column. When the rib cage is
Notes in Animal Physiology by CCDivina…………
46
elevated,
the
ribs
project
almost
directly forward and way from the spine,
increasing the anteroposterior thickness
of the chest. Muscles the raise the rib
cage are sternocleidomastoid, anterior
serrati. and scaleni. While the muscles
that depress the rib cage are abdominal
recti and internal intercostals.
Pressures that cause Movement of Air in
and out of the Lungs
Pleural pressure is the pressure of
the fluid in the narrow space between
the lung pleura and chest wall pleura.
During normal inspiration, the expansion
of the chest cage pulls the surface of
the lungs with greater force.
Alveolar pressure is the air inside
the lung alveoli. During inspiration,
the pressure in the alveoli decreases to
about negative one centimeter of water.
This
slight
negative
pressure
is
sufficient to move about 0.5 liter of
air into the lungs within 2 seconds
required
for
inspiration.
During
expiration opposite changes occur. The
alveoli pressure rises to about
+1 cm
of water and these forces the 0.5-liter
of inspired air out of the lungs during
the 2-3 seconds of expiration.
Lung compliance is the change in
lung volume for each unit change in
transpulmonary pressure. Transpulmonarv
pressure is the difference in pressure
Notes in Animal Physiology by CCDivina…………
47
between
the
alveolar
pleural pressure.
Surface
Lungs
Tension
and
pressure
Collapse
of
and
the
Water
molecules
have
a
strong
attraction for one another. The water
lining the alveoli also attempting to
contract. This attempts to force the air
out of the alveoli through the bronchi
and in doing so it causes the alveoli to
attempt to collapse. The net effect is
to cause an elastic contractile force of
the entire lungs, which is called the
surface tension elastic force.
Surfactant reduces the work of
breathing by decreasing the alveolar
surface tension. Smaller alveoli have a
greater tendency to collapse. When the
alveoli have one-half of the normal
radius,
the
collapse
pressure
are
double. Surfactant, interdependence, and
lung fibrous tissues are important for
stabilizing the sizes of the alveoli. If
some of the alveoli were small and
others were large, theoretically the
smaller alveoli would tend to collapse,
decreasing their volume in the lungs.
This
loss
of
volume
would
cause
expansion of the larger alveoli. But
interdependence,
fibrous
tissue
and
surfactant
are
reasons
why
that
instability of alveoli does not occur in
the normal lung.
Notes in Animal Physiology by CCDivina…………
48
Pulmonary Volumes and Capacities
Pulmonary
volumes
and
capacities
are
measured
with
a
spirometer, which is a drum that is
inverted in water with a tube extending
from the air space in the drum to the
mouth of the person being tested.
The pulmonary volumes added
together equal the maximum volume to
which the lungs can be expanded. The
four pulmonary volumes are: (1) tidal
volume; which is the volume of air
inspired or expired with each normal
breath, (2) inspiratory reserve volume;
the extra volume of air that can be
inspired over and above the normal tidal
volume, (3) expiratory reserve volume;
the extra amount of air that can be
expired by a normal tidal expiration,
(4) residual volume; is the volume of
air remaining in the lungs after the
most forceful expiration.
Pulmonary capacities are
combinations of two or more pulmonary
volumes, which can be described as (1)
Inspiratory
capacity
which
is
the
combination of tidal volume and the
inspiratory
reserve
volume,
(2)
Functional residual capacity, equals the
expiratory
reserve
volume
plus
the
residual volume, (3) Vital capacity,
equals the inspiratory reserve volume
plus
the
tidal
volume
plus
the
expiratory reserve volume, (4) total
Notes in Animal Physiology by CCDivina…………
49
lung capacity, it is equal to the vital
capacity plus the residual volume.
Functions of the Respiratory Passageway
Air is distributed to the lungs by
way
of
the
trachea,
bronchi
and
bronchioles. The trachea is called the
first generation respiratory passageway,
and two main rights and left bronchi are
the
second
generation
respiratory
passageways; each division thereafter is
an additional generation. There are
between 20-25 generations before the air
finally reaches the alveoli.
Respiratory Functions of the Nose
Warming and humidifying the air,
ordinarily,
the
temperature
of
the
inspired air rises to within one degree
Fahrenheit
of
body
temperature
and
within 2-3 % of flail saturation with
water
vapor
before
it
reaches
the
trachea.
Filtering the air, the hairs at
entrance to the nostrils are important
for filtering out large particles. The
air passing through the nasal passageway
hits
many
obstructing
veins:
the
conchae. septum, and pharyngeal wall.
When the particles strike the surfaces
of the obstructions, they are entrapped
in the mucous coating.
Pressures in the Pulmonary System
Notes in Animal Physiology by CCDivina…………
50
Blood pressure in the pulmonary
circulation is low compared with those
in systemic circulation. The left atrial
pressure can be estimated by measuring
the
pulmonary
wedge
pressure.
The
pulmonary wedge pressure can be measure
by floating a ballogn4ipped catheter
through the right heart and pulmonary
artery until the catheter wedges tightly
in smaller branches of the artery. The
wedge pressure is usually only 2-3 mm.Hg
greater than the left atrial pressure.
Pulmonary pressures are (1) pulmonary
artery
pressures;
(2)
pulmonary
capillary pressure and (3) left atrial
and pulmonary venous pressure.
Effect of Hydrostatic Pressure Gradients
in the Lungs
in the regional Pulmonary Blood flow
Hydrostatic gradients in the lung
create three zones of pulmonary blood
flow. Zone I has no blood flow during
any part of the cardiac cycle because
the local capillary pressure never rises
higher than the alveolar pressure. Zone
2 has an intermittent blood flow that
occurs during systole~ when the artery
pressure is greater than the alveolar
pressure. Zone 3 has a high continuous
blood
flow
because
the
capillary
pressure
remains
greater
than
the
alveolar pressure during the entire
cardiac cycle.
PHYSICAL PRINCIPLES OF GAS EXCIIANGE;
Notes in Animal Physiology by CCDivina…………
51
DIFUSION OF OXYGEN AND CARBON DIOXIDE
THROUGH THE RESPIRATORY MEMBRANE
Respiratory Gases Diffuse from
Areas of High Partial Pressure to Areas
of Low Partial Pressure.
Respiratory
physiology
involves
mixture
of
gases,
mainly
Oxygen, Nitrogen, and Carbon Dioxide.
The rate of diffusion of each of these
gases is directly proportional to the
pressure to the pressure caused by each
gas alone, which is called the partial
pressure of the gas. Partial pressures
are used to express the concentrations
of gases because it is the pressures
that causes the gases to move via
diffusion from one part of the body to
another.
The
partial
pressures
of
oxygen, carbon dioxide, and nitrogen are
designated
as
P02,
PC02,
and
PN2,
respectively.
The pressure of gas in the air is
calculated by multiplying its fractional
concentration by the total pressure. Air
has a composition of about 79% nitrogen
and about 21% oxygen. The total pressure
at sea level (atmospheric pressure)
averages 760 mm Hg; therefore 79% of the
760 mm Hg is caused by nitrogen (about
600 mm Hg) and 21 Hg is caused by oxygen
(about 160 mm Hg). The partial pressure
of nitrogen Ill the mixture is 600 mm
Hg, and the partial pressure of oxygen
is 160 mm Hg; the total pressure is 760
Notes in Animal Physiology by CCDivina…………
52
mm Hg, the sum of the individual partial
pressures.
The pressure of gas in a
solution is determined not only by its
concentration but also by its solubility
coefficient. Some types of molecules,
especially
carbon
dioxide,
are
physically or chemically attracted to
water molecules, which allows far more
of them to become dissolved without a
build-up of excess pressure within the
solution. The relationship between gas
concentration and gas solubility is
expressed by Henry's Law:
Concentration of dissolved gas
Pressure = Solubility Coefficient
The vapor pressure of
temperature is 47 mm Hg.
water
at
body
When air enters the respiratory
passageway, water evaporates from the
surfaces and humidifies the air. The
pressure that the water molecules exert
to escape from the surface is the vapor
pressure of the water, which is 47 mm Hg
at the body temperature. Once the gas
mixture has become fully humidified, the
partial pressure of water vapor in the
gas mixture is also 47 mm Hg. This
Partial pressure is designated PH2O.
The rate of gas diffusion in a fluid
(D)' is affected by multiple factors.
These factors are described as follows
Notes in Animal Physiology by CCDivina…………
53
and expressed in the following single
formula:
 Pressure difference the greater the
difference in pressure between the
two ends of a diffusion pathway,
the greater is the rate of gas
diffusion.
 Cross-sectional area (A)
the
greater the cross-sectional area of
the diffusion pathway, the greater
is the total number of molecules to
diffuse.
 Gas solubility (S) the greater the
solubility of the gas, the greater
is
the
number
of
m6lecules
available to diffuse for any given
pressure difference.
 Diffusion
distance
(d)
the
greater
the
distance
that
the
molecules must diffuse, the longer
it takes the molecules to diffuse
the entire the distance.
 Molecular weight of gas (MW) - the
greater the velocity of kinetic
movement of the molecules, which i~
inversely
proportional
to
the
square
root
of
the
molecular
weight, the greater the rate of
diffusion of the gas.
 Temperature
the
temperature
remains reasonably constant in the
body
an4
usually
need
not
be
considered.
The diffusion coefficient of a gas is
directly proportional to its solubility
Notes in Animal Physiology by CCDivina…………
54
and
inversely
proportional
to
its
molecular weight. It is obvious from the
above formula that the characteristics
of the gas determine two factors of the
formula
solubility
and
molecular
weight-and together they determine the
diffusion coefficient of the gas. That
is,
the
diffusion
coefficient
is
proportional
to
SVMW'~;
also,
the
relative rates at which different gases
at the same pressure levels diffuse are
proportional
to
their
diffusion
coefficients. Considering the diffusion
coefficient for oxygen to be 1, the
relative
diffusion
coefficient
for
carbon dioxide is 20.3. The
diffusion
coefficient
for
nitrogen,
carbon
monoxide, and helium are less than that
of oxygen.
COMPOSITION OF ALVEOLAR AIRIT'S RELATION TO ATMOSPHERIC AIR
The
concentrations
of
gases
in
alveolar air are different than those in
atmospheric air. These differences are
shown in the table. And explained as
follows:
1. Alveolar
air
is
only
replaced by atmospheric air
breath.
2. Oxygen is constantly being
from the alveolar air
3. Carbon dioxide is constantly
from the pulmonary blood
alveoli.
partially
with each
absorbed
diffusing
into the
Notes in Animal Physiology by CCDivina…………
55
4. Dry atmospheric air is humidified
before it reaches the alveoli.
Water vapor dilutes the other gases
in the inspired air. Atmospheric air is
composed mostly of nitrogen and oxygen;
it contains almost of nitrogen and
oxygen; it contains almost no carbon
dioxide or water vapor. The atmospheric
air becomes totally humidified as it
passes through the respiratory passages.
The
water
vapor
at
normal
body
temperature (i.e. 47 mm Hg) dilutes the
other gases in the inspired air. the
oxygen Hg in atmospheric air to 249 mm
Hg in the humidified air, and the
nitr6gen partial pressure decreases from
597 to 5634 mm Hg
Alveolar air is renewed very slowly
by
atmospheric
air.
The
amount
of
alveolar is replaced by new atmospheric
air with each breath is only one seventh
of the total, so that many breaths are
required to completely exchange
the
alveolar air. This slow replacement of
alveolar air prevents sudden change in
gas concentrations in the blood; makes
the respiratory control mechanisms much
mire stable that it would otherwise be;
and helps prevent excessive increases
and decreases in tissue oxygenation,
tissue carbon dioxide concentration, and
tissue
pH
when
respiration
is
temporarily interrupted.
Notes in Animal Physiology by CCDivina…………
56
The alveolar oxygen concentration
is controlled by the rate of oxygen
absorption into the blood and the rate
of entry of new oxygen into the lungs.
Oxygen is continually being absorbed
into the luings, and new oxygen is
continually being breathed into the
alveoli. The more rapidly oxygen is
absorbed,
the
lower
becomes
its
concentration
in
the
alveolus.
In
comparison, the more rapidly oxygen is
breathed into the alveoli from the
atmosphere,
the
higher
its
concentration.
Expired air is a combination of
dead space air and alveolar air. The
overall composition of expired air is
determined by the proportion of the
expired air that is dead space air and
the proportion of the expired air that
is alveolar air. When air is expired by
the lungs, the first pr6portion of this
air
(dead
space
air)
is
typical
humidified air. Then, more and more
alveolar air becomes mixed with the dead
space air until all the dead space air
has been washed out and only alveolar
air is expired at the end of expiration.
DIFFUSION
RESPIRATORY

OF
GASES
MEMBRANE
THROUGH
THE
A respiratory unit is composed of
respiratory
bronchiole,
alveolar
ducts, atria, and alveoli. There
are about 300 million units in the
Notes in Animal Physiology by CCDivina…………
57
two things. The alveolar walls are
extremely thin, and within them is
an
almost
solid
network
of
interconnecting
capillaries;
the
flow of blood in the alveolar wall
has been described as a sheet" of
flowing blood. Gas exchange occurs
through the membranes of all the
terminal portions of the lungs, not
merely ran the alveolar themselves.
These membranes are collectively
known as the respiratory membrane,
or the pulmonary membrane.





The
respiratory
membrane
is
composed
of
several
different
layers The exchange of oxygen and
carbon dioxide from the blood and
alveolar
air
requires
diffusion
through the
different layers of
the respiratory membrane:
A
layer
of
fluid
lining
the
alveolus that contains surfactant
The alveolar epithelium, which is
composed of thin epithelial cells.
Diffusion coefficient-The diffusion
coefficient for the transfer of
each gas through the respiratory
membrane depends on its solubility
in the membrane and, inversely, on
the square root of its molecular
weight.
Pressure
difference
across
respiratory
membraneThe
difference
between
the
partial
pressure of gas in the alveoli and
Notes in Animal Physiology by CCDivina…………
58
that of gas in t'1he blood is
directly proportional to the rate
of
gas
transfer
through
the
membrane.
DIFFUSING
MEMBRANE
CAPACITY
OF
THE
RESPIRATORY
The diffusing capacity of the lungs
for. carbon dioxide is 20 times greater
than that of oxygen. The ability of the
respiratory membrane to exchange a gas
between the alveoli and the pulmonary
blood can be expressed in quantitative
terms by its diffusing capacity, which
is defined as the volume of a gas that
diffuses
through
the
membrane
each
minute for a pressure difference of one
mm Hg. The diffusing capacity of the
lungs for oxygen when a person is at
rest is about 21 ml/mm Hg in minute. The
diffusing capacity for carbon dioxide is
about 20 times this value, or about 440
ml/mm Hg/minute.
The diffusion capacity for oxygen
increases
during
exercise.
During
exercise, the oxygenation of 'the blood
is
increased
not
only
by
greater
alveolar ventilation but also by greater
capacity of the respiratory membrane for
transmitting oxygen into the blood.
During strenuous exercise, the diffusing
'capacity for oxygen can increase to
about 65 ml/ mm Hg, which is three times
the diffusing capacity during resting
Notes in Animal Physiology by CCDivina…………
59
conditions. This increase is caused by
the ff:
Increased surface area- Opening up of
closed pulmonary capillaries or extra
dilatation of open capillaries increases
the
surface
area
for
diffusion
of
oxygen.
Improved ventilation-perfusion ratio Exercise improves the match between the
ventilation of the alveoli and the
perfusion of the alveolar capillaries
with the blood.
Respiratory Membranes:
An epithelial basement membrane
A thin interstitial space between
the alveolar epithelium
Capillary membrane
A capillary basement membrane that
fuses in places with the epithelial
basement membrane
The
capillary
endothelial
membrane.
The respiratory membrane
for gas exchange:


is
optimized
Membrane
thickness--Despite
the
large number of layers, the overall
thickness of respiratory membrane
averages
about
0.6
micrometer
except where there are cell nuclei.
Membrane
surface
area-The
total
surface area of the respiratory
membrane is about 70 square meters
Notes in Animal Physiology by CCDivina…………
60


in the normal adult. This is
equivalent to the floor area of a
25-by-30- foot room
Capillary
blood
volume-The
capillary blood volume is 60 to 140
milliliters. By imagining that this
in all amount of blood is spread
over the entire surface of a 25-by30-foot
floor,
it
is
easy
to
understand
the
rapidity
of
respiratory exchange of gases.
Capillary
diameter-The
average
diameter
of
the
pulmonary
capillaries is about 5 micrometers;
the red blood cell membrane usually
touches the capillary wall so that
the oxygen and carbon dioxide need
not pass through the significant
amounts of plasma as they diffuse
between the alveolus and the red
cells.
Multiple factors determine how rapidly a
gas will pass through the respiratory
membrane.
These
determining
factors
include the ff:

Thickness of respiratory membraneThe rate of diffusion through the
membrane is inversely proportional
to the membrane thickness. Edema
fluid in the interstitial space and
alveoli decreases diffusion because
the respiratory gases must move
only through the membrane but also
through this fluid. Fibrosis of the
lungs
can
also
increase
the
Notes in Animal Physiology by CCDivina…………
61
thickness of some portions of the
respiratory membrane.

Surface
area
of
respiratory
membrane- In emphysema; many in the
alveoli coalesce, with dissolution
of
alveolar
walls:
This
often
causes the total surface area to
decrease by as much as five folds.
During strenuous exercise. Even the
slightest decrease in surface area
can be a serious detriment to
respiratory exchange of gases.
TRANSPORT OF OXYGEN AND CARBON DIOXIDE
IN THE BLOOD and BODY FLUIDS
OXYGEN is transported principally
in combination with hemoglobin to the
tissue capillaries, where it is released
for use by the cells.
In tissue cells, oxygen reacts with
various
foodstuffs
to
form
large
quantities
of
carbon
dioxide.
This
enters the tissue capillaries and is
transported back to the lungs.
Pressures of Oxygen and Carbon Dioxide
in the Lungs, Blood and Tissues
The P02 of pulmonary blood rises to equal
that of alveolar air within the first
third of the capillary
The P02 averages 104 mm Hg in the
alveolus, whereas the P02 of venous blood
Notes in Animal Physiology by CCDivina…………
62
entering the capillary averages only 40
mm Hg. The initial pressure difference
that causes oxygen to diffuse into the
pulmonary capillary is 104-40 mm Hg, or
64 mm Hg. The P02 rises to equal that of
alveolar air by the time the blood has
moved a third of the distance through
the capillary, becoming almost 104 mm
Hg.
Tissue P02 is determines by the rate of
oxygen transport to the tissues and the
rate
of
oxygen
utilization
by
the
tissues.
The P02 in the initial portions of
the capillaries is 95 mm Hg, and the P02
in the interstitial fluid surrounding
the tissue cells averages 40 mm Hg. This
pressure difference causes oxygen to
diffuse rapidly from the blood into the
tissues, and the P02 of the blood
leaving the tissue capillaries is also
about 40 mm Hg. Two main factors can
affect the tissue P02.
1. Rate of Blood Flow. If the blood
flow through a particular tissue becomes
increase, greater quantities of oxygen
are transported into the tissue in a
given period, and the tissue P02 becomes
correspondingly increased.
2. Rate of Tissue Metabolism. If
the cells use more oxygen for metabolism
than normal, the interstitial fluid P02
tends to reduce.
Notes in Animal Physiology by CCDivina…………
63
Carbon dioxide diffuses in a direction
exactly opposite that of oxygen. There
is one major difference between the
diffusion of carbon dioxide and oxygen:
carbon dioxide can diffuse about 20
times as rapidly as oxygen
TRANSPORT OF OXYGEN IN THE BLOOD
About 97 percent of the oxygen are
carried to the tissues in chemical
combination with hemoglobin
The remaining 3 per cent are carried
to the tissues in the dissolved state in
the water of the plasma and cells.
Hemoglobin
combines
with
large
quantities of oxygen when the P02 level
are low. When blood passes through the
lungs, where the blood P02 rises to 95
mm
Hg,
hemoglobin
picks
up
large
quantities of oxygen. As it passes
through the tissue capillaries, where
the P02 falls to about 40 nm Hg, large
quantities of oxygen are released from
the hemoglobin. The free oxygen then
diffuses to the tissue cells.
Carbon monoxide interferes with the
oxygen transport because it has about
250 times the affinity of oxygen for
hemoglobin
Carbon
monoxide
combines
with
hemoglobin at the same point on the
hemoglobin molecule, as does oxygen and
can therefore displace oxygen from the
Notes in Animal Physiology by CCDivina…………
64
hemoglobin. Because it binds with about
250 times as much as tenacity as oxygen,
relatively
small
amount
of
carbon
monoxide can tie up a large portion of
the hemoglobin, making it unavailable
for oxygen transport. A patient with
severe carbon monoxide poisoning can be
helped by the administration of pure
oxygen because oxygen at high alveolar
pressure displaces carbon monoxide from
its combination with hemoglobin more
effectively than does oxygen at low
atmospheric pressures.
TRANSPORT OF CARBON DIOXIDE IN THE BLOOD
Under resting conditions, about 4
milliliters
of
carbon
dioxide
are
transported from the tissues to the
lungs in each 100 millimeters of blood
Approximately 70 percent of the
carbon dioxide is transported in the
form of bicarbonate ions, 23 percent is
transported in combination of hemoglobin
and plasma proteins, and 7 percent is
transported in the dissolve state in the
fluid of the blood.
Transport in the form of bicarbonate
ions (70 %). Dissolved carbon dioxide
reacts with water inside red blood cells
to form carbonic acid. An enzyme in the
red
blood
cells
called
carbonic
anhydrase catalyzes this reaction. Most
of
the
carbonic
acid
immediately
dissociates into bicarbonate ions and
Notes in Animal Physiology by CCDivina…………
65
hydrogen ions; the hydrogen ions in turn
combine with hemoglobin. Many of the
bicarbonate ions diffuse from the red
blood
cells
into
the
plasma
while
chloride ions diffuse into the red blood
cells to take their place, a phenomenon
called the chloride shift.
Transport
in
combination
with
hemoglobin and plasma proteins (23%).
Carbon dioxide reacts directly with
amine
radicals
of
the
hemoglobin
molecules and plasma proteins to form
the compound carbaminohemoglobin. This
combination of carbon dioxide with the
hemoglobin is a reversible reaction that
occurs with a loose bond, so that the
carbon dioxide is easily released into
the alveoli where the where the PC02 is
lower
than
that
in
the
tissue
capillaries.
Transport in the dissolved state (7%).
The amount of carbon dioxide dissolved
in the fluid of the blood at 45-mm Hg is
about 2.7 milliliters per 100 ml of
blood (2.7 volumes percent). The amount
dissolved at 40 mm Hg is about 2.4 ml,
or a difference of ()~3ml. Therefore,
only about 0.3m1 of carbon dioxide is
transported in the form of dissolved
carbon dioxide by each lOOml of blood;
this represents about 7% of all carbon
dioxide that is transported.
Notes in Animal Physiology by CCDivina…………
66
REGULATION OF RESPIRATION
Respiratory Center
1. The dorsal respiratory group – generates
inspiratory
action
potentials
in
a
steadily increasing ramp-like fashion
and thus is responsible for the basic
rhythm of respiration
2. The pneumotaxic Center - helps to control
the rate and pattern of breathing. It
transmits inhibitory signals to the
dorsal
respiratory
group
and
thus
controls
the
filling
phase
of
the
respiratory cycle.
3.
The ventral respiratory group - can
cause either expiration or inspiration,
depending on which neurons in the group
are stimulated
The Hering - Breuer reflex prevents
over inflation of the lungs. This reflex
is initiated by nerve receptors located
in
the
walls
of
the
bronchi
and
bronchioles that detect the degree of
stretch of the lungs. When the lungs
become overly inflated, the stretch
receptors
activate
an
appropriate
feedback response that "switches off'
the inspiratory ramp and thus stops
further inspiration.
Chemical Control of Respiration
Notes in Animal Physiology by CCDivina…………
67
1. The ultimate goal of respiration is
to maintain proper concentrations of
oxygen, carbon dioxide, and hydrogen
ions in the tissues. Excess carbon
dioxide
or
hydrogen
ions
mainly
stimulate
the
respiratory
center
itself, causing increased strength of
inspiratory and expiratory signals to
the respiratory muscles.
2. Increased
PCO2
or
hydrogen
ion
concentration
stimulates
a
chemosensitive
area
of
the
respiratory
center.
The
sensor
neurons in the chemosensitive neurons
compared with carbon dioxide.
Regulation
Exercise
of
Respiration
during
1. In strenuous exercise, the arterial
P02, PC02 and pH
values remain
almost
exactly
normal.
Strenuous
exercise
can
increase
oxygen
consumption
and
carbon
dioxide
formation by as much as 20-fold.
2. Chemical factors can also play a role
in the control of respiration during
exercise. When a person exercises,
the nervous factors usually stimulate
the respiratory center by the proper
amount to supply the extra oxygen
requirements for the exercise and the
blow off the extra carbon dioxide.
Other factors that affect Respiration
Notes in Animal Physiology by CCDivina…………
68
1. Voluntary
control
One
can
hyperventilate or hypoventilate to
such
an
extent
that
serious
derangement in PCO2, PH, and P02 can
occur in the blood.
2. Irritant receptors in the airways The
epithelium
of
the
trachea,
bronchi, and bronchioles is supplied
with sensory nerve endings called
pulmonary irritant receptors that are
stimulated by some irritants that
enter the respiratory airways.
3. Lung "J receptors" - a few sensory
nerve endings occur in the alveolar
wall
in
justaposition
to
the
pulmonary capillaries, and they are
called 3 receptors.
4. Brain edema - The activity of the
respiratory center may be depressed
or even inactivated by acute brain
edema resulting from concussion.
5.
Brain edema
The activity of the
respiratory center may be depressed
or even inactivated by acute brain
edema resulting from concussion.
6.
Anesthesia - Perhaps the most
prevalent
cause
of
respiratory
depression and respiratory arrest is
overdose
with
anesthetics
or
narcotics.
Methods
for
Abnormalities
Studying
Respiratory
The
most
fundamental
tests
of
pulmonary performance are determinations
of the blood P02, PC 02, and pH. it is
Notes in Animal Physiology by CCDivina…………
69
often
important
to
make
these
measurements
rapidly
as
an
aid
in
determining the appropriate therapy for
acute respiratory distress or acute
abnormalities
of
acid-base
balance.
Measuring devices for pH, PCO2, and P02,
are built into the same apparatus, and
all these measurements can be made
within a minute or so with one small
sample of blood; thus, changes in the
blood gases and pH can be followed
almost moment by moment.
Respiratory Disorders
Chronic Pulmonary Emphysema
The term pulmonary emphysema literally
means excess air in the lungs. Chronic
pulmonary emphysema, however, signifies
a complex obstructive and destructive
process of the lungs and is usually a
consequence of long-term smoking The
following
pathophysiological
events
contribute to its development:
· Chronic infection
the bronchi and
bronchioles
are
irritated.
The
irritant (usually smoke) deranges the
normal protective mechanisms of the
airways: (1) cilia may be partially
paralyzed so that mucus cannot be
moved easily out of the passageways,
(2)
secretion
of
excess
mucus
exacerbates the condition, and (3)
alveolar
macrophages
can
be
inhibited.
Notes in Animal Physiology by CCDivina…………
70
· Airway obstruction - the infection,
excess mucus, and inflammatory edema
of the bronchiolar epithelium combine
to cause chronic obstruction of many
of the smaller airways.
· Destruction of alveolar walls - the
obstruction of the airways makes it
especially
difficult
to
expire,
causing entrapment of air in the
alveoli and over stretching of the
alveoli. This, combined with lung
infection, causes marked destruction
of the alveolar cells.
Pneumonia
The
term
pneumonia
includes
any
inflammatory condition of the lung in
which alveoli are filled with fluid and
blood cells. A common type of pneumonia
is bacterial pneumonia, caused most
frequently by pneumococci. This disease
begins with infection in the alveoli;
the pulmonary membrane becomes inflamed
and highly porous, so that find and even
red and white blood cells pass out of
the blood into the alveoli. The infected
alveoli become progressively filled with
fluid and cells, and the infection
spreads by extension of bacteria from
alveolus to alveolus. Eventually, large
area of the lungs, sometimes whole lobes
or
even
a
whole
lung,
become
"consolidated" which means that they are
filled with fluid and cellular debris.
Notes in Animal Physiology by CCDivina…………
71
Some Questions and Answers

What is respiration? Why do animals
respire and why is it important?
Respiration is the process by which
animals take in oxygen necessary for
cellular metabolism and release the
carbon dioxide that accumulates in their
bodies as a result of the expenditure of
energy. When an animal breathes, air or
water is moved across such respiratory
surfaces as the lung or gill in order to
help with the process of respiration.
Oxygen must be continuously supplied to
the animal and carbon dioxide, the waste
product, must be continuously removed
for cellular metabolism to function
properly. For example, if this does not
happen
and
carbon
dioxide
levels
increase in the body, pH levels decrease
and the animals may eventually die
Oxygen is valuable because it is
important in many ATP-producing cycles
occurring throughout the body such as,
the
Krebs
cycle,
and
the
electron
transport chain. Glycolysis breaks down
glucose, a six-carbon sugar, into the
three-carbon molecule of pyruvic acid.
The series of reactions associated with
glycolysis are necessary for anaerobic
and aerobic pathways to work, and are
also the most fundamental in cellular
metabolism. In the presence of 02, the
pyruvic acid, which came about from the
breakdown
of
glucose,
is
further
Notes in Animal Physiology by CCDivina…………
72
oxidized.
However,
under
anaerobic
conditions the pyruvic acid is reduced
to lactic acid. Glycolysis follows a
specific pathway and ultimately, the
oxidation of 1 mol of glucose to pyruvic
acid ends in a net gain of only 2 mol of
ATP and 2 NADH molecules.
The Krebs cycle is a series of
eight
major
reactions
following
glycolysis. In these reactions, acetate
residues are degraded to CO2 and H2O.
With each turn of the Krebs cycle, 2 CO2
molecules and 8 H+ atoms are removed.
These hydrogen atoms, which are removed
two at a time, are transported by NADH
and FADH2 and further go into the
electron transport chain.
The electron transport chain, also
known as the respiratory chain, oxidizes
the NADH and FADH2 from the Krebs cycle
to H2O by oxygen. This cycle involves
electrons that move through about seven
steps in order of their decreasing
electron pressures, more specifically,
from the high reducing potential of NADH
to FADH2 to oxygen, the final electron
acceptor. The electron transfer is the
final pathway for all electrons during
aerobic metabolism, and it uses the
energy
from
the
transfer
for
the
phosphorylation of ADP to ATP. A total
of 38 ATP molecules are collectively
released
from
the
three
cycles
of
glycolysis, the Krebs cycle, and the
electron
transport
chain
working
Notes in Animal Physiology by CCDivina…………
73
together. Without oxygen, the Kreb's
cycle and electron transport chain would
be disabled and only 2 ATPs would be
produced by glycolysis.
To maintain an
adequate supply of oxygen to cells,
animals must have an efficient means of
gas transfer and respiration.

What is oxygen debt?
In some animals, such as mammals,
if the supply of oxygen to active muscle
cells is not sufficient to produce
enough ATP to maintain intense activity,
the only source of additional ATP will
be from glycolysis.
Without sufficient
oxygen,
some
of
the
pyruvic
acid
produced is reduced to lactic acid,
which
accumulates
in
the
tissues,
resulting in fatigue.
Excess lactic
acid
may
also
enter
the
blood,
decreasing blood pH and affecting other
tissues
in
the
body.
When
muscle
activity decreases, extra oxygen is
needed to convert the lactic acid back
to pyruvic acid, which is then utilized
by the Kreb's cycle.
This extra oxygen
represents the animal's oxygen debt.
Some animals, such as the goldfish and
some intertidal invertebrates, can avoid
oxygen
debt
through
the
use
of
biochemical pathways that convert lactic
acid to alcohol, which can then be
excreted.
Notes in Animal Physiology by CCDivina…………
74

What is the difference between air
and
water
as
respiratory
environments? How does this affect
the
amount
of
energy
spent
obtaining oxygen in water and air
and therefore the structures used
in ventilation?
Water
and
air
are
radically
different as respiratory environments in
a number of ways. The most significant
difference is that water contains only
1/13 as much O2 as air does, or 1% to 21%
(water to air) by volume. Water also is
over 800 times denser than air and 50
times more viscous, so aquatic breathers
must use more energy to simply move
water across their respiratory surfaces.
Fish, for example, use as much as 10%
of the oxygen they take in to provide
breathing muscles with enough oxygen to
burn the energy needed to keep water
passing over the gills in the right
direction.
Humans use only 1-2 % of
their oxygen intake to keep breathing.
Temperature also has an effect on the
amount of oxygen each environment can
hold. As water temperature increases the
amount of dissolved oxygen decreases.
Air also shows a slight reduction in
oxygen
content
with
increasing
temperature,
but
it
isn't
physiologically
significant
because
there is so much oxygen in air to begin
with.
Gas diffusion rates are also
Notes in Animal Physiology by CCDivina…………
75
lower in water than in air.
Salt water
contains less oxygen than fresh water
because the higher salt concentration
decreases gas solubility.
All of this
produces
a
vast
difference
between
aquatic and terrestrial organisms in the
amount of energy expended to obtain
oxygen.

How is oxygen carried through the
blood and passed onto other cells?
What role does hemoglobin play in
oxygen transfer? What conditions
affect hemoglobin/oxygen affinity?
Hemoglobin (Hb) is found in red
blood cells, being the principle part of
a red blood cell. Hemoglobin is a large
protein with four polypeptide chains and
four heme groups. Each heme group has an
iron atom attached to it, which is where
oxygen attaches to be carried to cells
and tissues. It is important to note
that the O2/Fe bond, that is initially
made so the oxygen can be transported,
can be readily broken in the right
conditions. These conditions are altered
depending on if oxygen needs to be
picked up or released to tissue cells.
The reason hemoglobin is found in red
blood cells only is that the conditions
needed for efficient oxygen transport by
the Hb molecules can be quickly changed,
and all of this can be done without
changing the conditions throughout the
body. Some of the conditions necessary
for oxygen and carbon dioxide transport
Notes in Animal Physiology by CCDivina…………
76
may be unsuitable for other reactions
that need to take place throughout the
body, so keeping Hb within the red blood
cells allows oxygen transport to occur
without interfering with other bodily
functions. Conditions that control the
ability of
hemoglobin (Hb) to bind to
oxygen include the partial pressure of O2
in the surrounding respiratory medium
(air or water), temperature, pH, CO2
levels. A high partial pressure of O2 in
the surrounding respiratory medium will
increase the rate at which the O2
diffuses into the blood.
Hemoglobin's
affinity for oxygen typically decreases
if temperature increases, pH decreases,
or CO2 levels increase.
There are a few different kinds of
hemoglobin, all doing the same job, but
each having its own affinity to O2.
Normally hemoglobin will pick up an O2
when the partial pressure of the O2 in
the blood (O2 dissolved in solution) is
high, and there are fewer than 4 O2
molecules on the hemoglobin, 4 being the
maximum number able to be carried. When
an
O2
molecule
is
attached
to
a
hemoglobin molecule it is not affecting
the partial pressure of the O2 in the
blood, as there is a low concentration
of O2 in the blood plasma, just not
enough to supply the cells of the body.
The best scenario for oxygen transfer
from the lungs to body cells and tissues
is hemoglobin to have high affinity at
the respiratory surface (high amount of
Notes in Animal Physiology by CCDivina…………
77
O2 diffusing across the lung surface)
and low oxygen affinity (give the oxygen
away) near body cells that need it (low
O2 content).
Other
factors
that
affect
hemoglobin/oxygen
affinity
include
a
decrease
in
pH,
which
reduces
hemoglobin/oxygen
affinity
(the
Bohr
effect). A decrease in pH reduces Hb/ O2
affinity
because
the
shape
of
the
oxygen-binding sites of the hemoglobin
molecule
changes,
making
it
more
difficult for them to bind to oxygen.
(See "Why are red blood cells important
to carbon dioxide transport?" for a
complete explanation of the mechanisms
involved). A rise in body temperature
reduces Hb/O2 affinity as the increased
energy (heat) will prevent bonds from
forming or break bonds currently in
place. Increased CO2 content can affect
the affinity because CO2 can bind to
sites where O2 would normally bind.
Hemoglobin normally picks up CO2 at the
tissues
and
releases
it
at
the
respiratory surface in
exchange for
oxygen to complete the chain. When the
concentration of CO2 is too high it takes
the place of oxygen on Hb at higher than
normal rates.
Oxygen
dissociation
curves
graphically represent the percent of
hemoglobin's oxygen binding sites that
are holding oxygen at different partial
pressures of oxygen.
The sigmoid (SNotes in Animal Physiology by CCDivina…………
78
shaped)
curve
is
due
to
subunit
cooperativity between the four oxygen
binding sites on a hemoglobin molecule.
When no binding sites are occupied by
oxygen, it is relatively difficult to
get the first oxygen to bind.
After it
does, however, the structure of the
hemoglobin molecule is altered a bit,
and the second binding site becomes more
accessible. This makes it a bit easier
for the second molecule of oxygen to
bind.
After this, additional oxygen
molecules bind rather easily to the
third
and
fourth
binding
sites.
Therefore, oxygen binds slowly at first,
and
then
more
quickly,
giving
the
dissociation curve a sigmoid shape.

How is carbon
in the blood?
dioxide
transported
The
transportation
of
carbon
dioxide is a very significant process of
the gas-transfer systems within many
animals. There are three main ways in
which CO2 is transported in the blood. A
small percentage of the CO2 that is in
the blood is dissolved molecular CO2. A
larger amount of CO2 reacts with –NH2
groups of hemoglobin and other proteins
to form carbamino compounds.
However,
most of the CO2 that is transported in
the blood is in the form of bicarbonate
(HCO3-). In general, CO2 is diffused into
the blood from the tissues. The blood
transports
CO2
to
the
respiratory
surfaces of the lungs or gills, where it
Notes in Animal Physiology by CCDivina…………
79
is released into the environment. The
blood mainly consists of plasma and
erythrocytes (red blood cells). Most of
the CO2 entering and leaving the blood
does so through erythrocytes.

Why are red blood cells important
to carbon dioxide transport?
Most of the CO2 entering or leaving
the blood go through red blood cells for
two reasons. One reason is due to the
enzyme carbonic anhydrase. This enzyme
is present in red blood cells and not in
the plasma. The enzyme is important in
the transportation of CO2 because, within
the red blood cells, it catalyzes the
reaction of CO2 with OH- resulting in the
formation of HCO3- ions. As the level of
HCO3ions
increases
within
the
erythrocytes, the HCO3- ions diffuse
through the erythrocyte membranes into
the plasma of the blood. In order to
maintain electrical balance within the
erythrocytes, an anion exchange occurs
in a process called a chloride shift. In
this process, HCO3- ions leave the red
blood cells while a net influx of Clions from the plasma enters the red
blood cells. The membrane of red blood
cells is very permeable to both ions
because
the
membrane
has
a
high
concentration of a special anion carrier
protein, the band III protein. This
protein allows for a passive diffusion
of the Cl- and HCO3- ions to and from the
red blood cells and plasma. This keeps
Notes in Animal Physiology by CCDivina…………
80
the bicarbonate from building up in the
red blood cells, which would slow down
or stop the reversible conversion of CO2
to HCO3-. Facilitated diffusion occurs in
the
movement
of
CO2
across
the
respiratory
surfaces
as
bicarbonate
(HCO3-) diffuses out of the red blood
cells and into the epithelium where it
is converted back to CO2. Excretion of
CO2
is
limited
by
the
rate
of
bicarbonate-chloride exchange across the
erythrocyte membrane.
The second reason why most of the
CO2 is transported to and from the blood
by passing through the erythrocytes is
that O2 binds to Hemoglobin (Hb) at the
respiratory surface, causing hydrogen
ions (H+) to be released. The increase in
H+ ions combines with HCO3- to form CO2
and OH-. Thus, more CO2 is formed and can
leave the blood across the respiratory
surface. Excess H+ binds to OH-, forming
water and allowing the pH to increase
enough to promote the binding of oxygen
to Hb. The release of O2 from Hb in the
tissues makes the Hb available to bind
to H+, promoting the conversion of CO2 to
HCO3-, which helps draw CO2 from the
tissues. Therefore, CO2 that is being
transported into and out of the red
blood cells minimizes changes in pH in
other parts of the body because of
proton binding to and proton release
from hemoglobin, as it is deoxygenated
and
oxygenated,
respectively
(Figure
1.).
Notes in Animal Physiology by CCDivina…………
81

Why is the
important?
regulation of body pH
The
regulation
of
body
pH
is
important because some organs, tissues,
and various types of cells are more
affected by changes in pH than others.
Therefore, within an animal’s body are
various mechanisms, including mechanisms
at the cellular level, that regulate the
body pH in order for the animal to
maintain normal bodily functions. For
example, the regulation of body pH is
needed in animals in order to stabilize
volume of hydrogen ions and to regulate
enzyme activity. Within cells, pH is
regulated
in
order
for
cellular
functions to proceed. At the tissue
level, the body has the ability to
Notes in Animal Physiology by CCDivina…………
82
redistribute
acid
between
body
compartments because some tissues have
the ability to tolerate much larger
fluctuations in pH than others do. In
general, animals have a body pH that is
on the alkaline side of neutral, which
means that there is less hydrogen than
hydroxyl ions in the body. Human blood
temperature) has a pH of 7.4. Normal
functioning can be maintained in mammals
at 37º C over a blood plasma
pH range
of 7.0-7.8.

How does breathing regulate pH?
One of the main ways that a mammal
regulates pH is through the control of
respiration. For example, if the body pH
in a mammal decreases, the respiration
rate and depth of respiration increases
in order to get rid of the excess CO2,
which brings H+ levels back down and
brings pH back up. Hence, when breathing
is increased, CO2 levels in the blood
decline
and
pH
increases.
If
pH
increases, respiration rate decreases,
thereby increasing CO2 levels, which
forms more carbonic acid and brings pH
back down.

In mammals, a stable body pH is
achieved by adjusting the release
of
CO2
through
the
lungs
and
excretion of acid or bicarbonate
through the kidneys, so that acid
excretion
and
production
are
Notes in Animal Physiology by CCDivina…………
83

balanced. The collecting duct of
the mammalian kidney has acidexcreting and base-excreting cells,
which can be altered to increase or
decrease acid or base excretion. In
aquatic
animals,
the
external
surfaces
have
the
capacity
to
extrude acid in similar ways to the
collecting duct of the mammalian
kidney. For example, a protein
ATPase exists in the skin of frogs
and gills of freshwater fish which
excretes protons on the apical
surface of the epithelium. Fish
gills also have a HCO3-/Cl- exchange
mechanism,
which
aids
in
the
regulation of body pH.
What are alkalosis and acidosis,
and what are the consequences?
When an animal’s body experiences
changes
in
its
body
pH,
many
physiological changes occur within the
body of the animal. When there is
excessive alkalinity in the body and
therefore an increase in body pH, this
is
referred
to
as
alkalosis.
Conversely, when there is excessive
acidity in the body and therefore a
decrease in body pH, this is termed
acidosis.
In terms of the effects of pH on
the respiration of animals, when lung
ventilation is decreased causing CO2
excretion to drop below CO2 production,
body CO2 levels rise and pH falls. This
Notes in Animal Physiology by CCDivina…………
84
is referred to as respiratory acidosis.
When
lung
ventilation
is
increased
causing CO2 excretion to rise above CO2
production, body CO2 levels fall and pH
rises.
This
is
referred
to
as
respiratory alkalosis.
It is important to know that body
fluids are electroneutral, which means
that the sum of the anions equals the
sum of the cations. Respiratory acidosis
and
alkalosis
disturb
the
electroneutrality of the body fluids.
However, at the cellular levels, the pH
is regulated and electroneutrality is
brought back to the body fluids. There
are various mechanisms, which regulate
cellular
pH
and
thus
maintain
electroneutrality in the body fluids.
One
cellular
mechanism
involves
proteins and phosphates within the cell
that act as physical buffers to regulate
cellular pH. The most important buffers
in the blood are proteins, especially
hemoglobin, and bicarbonate because the
CO2-to-bicarbonate ratio can be adjusted
by excretion of CO2 in order to regulate
pH.
A second mechanism that regulates
cellular
pH
involves
the
important
+
reaction of HCO3
with H
ions. For
example, when oxygen enters red blood
cells within the blood, the molecules
attach to the hemoglobin thus releasing
H+
ions.
The
pH
decreases,
which
Notes in Animal Physiology by CCDivina…………
85
increases cellular acidity and causes
the reaction of HCO3- with H+ ions to
form CO2. The CO2 then diffuses out of
the red blood cells thus regulating the
pH within the cells.
Also the proton-exchange and the
anion-exchange mechanisms in the cell
membrane
play
important
roles
in
adjusting cellular pH. For example, if a
cell is acidified, there is a H+ efflux,
which is connected to a Na+ influx and
there is a HCO3- influx, which is
connected to Cl- efflux. This mechanism
adjusts the pH of the cell to a less
acidified
state.
Lastly,
another
mechanism for regulating cellular pH
involves the simple passive diffusion or
active transport of H+ ions from the
cells.

What are the organs that facilitate
gas exchange/respiration?
Gas transfer occurs by passive
diffusion from the environment across
the body surface. Air breathing, in most
vertebrate
animals,
involves
the
movement of air into and out of the
lungs. Insects have developed a very
different method of gas transfer between
the tissues and the environment and this
includes
a
tracheal
system.
Water
breathing, on the other hand, for most
aquatic
animals
involves
a
unidirectional flow of water over the
gills. Thus, the structure and design of
Notes in Animal Physiology by CCDivina…………
86
the
mammalian,
insect,
and
fish
respiratory
systems
are
radically
different. Each gas-transfer system is
built according to the needs of the
animal and to the medium in which it
lives.
In
air
breathing
animals,
the
related
respiratory
organ
that
facilitates gas transfer, is the lung.
The lungs in air breathing vertebrates
are large organs of respiration located
in the chest cavity. In humans, the
right lung is made up of three lobes and
the left lung is composed of two lobes.
They are suspended in the pleural cavity
and opens to the outside by the trachea.
The respiratory portion of the lung
includes the terminal bronchioles (under
glossary
term
as
bronchus),
the
respiratory
bronchioles,
and
the
alveolar ducts and sacs.
In
contrast,
the
associated
respiratory organs of the fish include
the gills. The gills consist of a
feathery,
branched
tissue
richly
supplied with blood vessels. The gills
facilitate the exchange of oxygen and
carbon dioxide
with the surrounding
water.
Most insects respire by means of a
tracheal system. In this system, gas is
directly transported to the tissues by
air-filled tubules that bypass blood.
The
pores
to
the
outside,
called
Notes in Animal Physiology by CCDivina…………
87
spiracles,
deliver
the
gases
of
respiration. The drawback of this system
is that the gases diffuse slowly in the
long narrow tubules; as a result, these
tubes need to be limited in size for
adequate gas transfer. The advantage is
that O2 and CO2 diffuse much faster,
10,000 times faster, from the air than
in
water,
blood,
or
tissues.
This
feature often uses less energy for
ventilation and bypasses the need for a
circulatory system.
Another advantage
of the tracheal system is that oxygen
can be delivered directly to tissues
that need it, such as flight muscles.

What are the components
mammalian lung?
of
the
The mammalian lung is more complex than
that of the amphibian, reptile, or other
non-mammal species, and consists of a
complex network of tubes and sacs. To be
more specific, the human respiratory
system consists of the nasal cavity,
pharynx, trachea, bronchi, and lungs.
Although not considered a part of the
respiratory system, the ribs, muscles,
and diaphragm are important and help in
the expansion and contraction of the
lung. To begin with, the pharynx and
larynx lead to the lungs; the larynx is
connected to the trachea, which branch
into the right and left bronchi. These
bronchi further divide and lead to the
terminal
bronchioles.
The
terminal
bronchioles continue and then lead air
Notes in Animal Physiology by CCDivina…………
88
to the respiratory bronchioles. The
respiratory
bronchioles
themselves
connect to a fan of alveolar ducts and
sacs. The function of the alveolar ducts
and sacs is to moisten and cleanse the
air taken in, and furthermore, transfer
it to the gas-exchanging portion of the
lung. These alveolar ducts and sacs are
filled
with
many
capillaries,
the
smallest of the blood vessels, and also
consist of connective tissue fibers.
Alveoli, millions of interconnected
sacs, also make up a large part of the
lung. The human lung is made up of an
average of 300 million alveoli. Through
diffusion, gases from the air in the
alveoli are exchanged with the gases in
the
pulmonary
capillary
blood.
The
transport of gases depends on this
exchange and relationship between O2
pressure
in
the
alveoli
and
the
surrounding atmospheric pressure.
As
seen,
through
a
series
of
branches and smaller ducts, air is
delivered to the respiratory portion of
the lung (the terminal bronchioles,
respiratory
bronchioles,
and
the
alveolar
ducts
and
sacs);
gas
is
transferred
across
the
respiratory
epithelium in these specific areas. Gas
transfer also occurs across acini and
the pores of Kohn, which allow for
collateral (side-by-side) movement of
air.
Notes in Animal Physiology by CCDivina…………
89

How do different animals ventilate
their
lungs/spiracles?
(mammals,
birds,
reptiles,
frogs,
invertebrates)
The functional anatomy of the lungs and
associated structures vary considerably
among
animals
in
the
mechanism
of
lung/spiracle ventilation.
Mammals. The lungs of mammals are
elastic,
multi-chambered
bags,
which
open to the exterior through a single
tube, called the trachea. The lungs are
suspended within the pleural cavity. The
ribs and the diaphragm form the walls of
the pleural cavity, which are referred
to as the thoracic cage. The thoracic
cage mostly consists of the lungs, but
between the lungs and the thoracic walls
there is a low-volume of pleural space
sealed and fluid filled.
During
normal
breathing,
the
thoracic cage expands and contracts by a
series
of
skeletal
muscles,
the
diaphragm, and the external and internal
intercostal
muscles.
The
respiratory
center within the
medulla oblongata
controls
the
contractions
of
these
muscles through the activity of motor
neurons. During inhalation, the volume
of the thorax increases due to the
lowering of the diaphragm. In addition,
the ribs are raised and moved outward by
the
contraction
of
the
external
intercostal muscles. The increase in
Notes in Animal Physiology by CCDivina…………
90
thoracic
volume
reduces
alveolar
pressure, and air is drawn into the
lungs. During exhalation the diaphragm
and external intercostal muscles relax,
reducing the thoracic volume. Reducing
the thoracic volume raises alveolar
pressure and forces air out of the
lungs.
Birds. In the lungs of birds, gas
exchange
occurs
in
air
capillaries
extending from parabronchi, a series of
small tube-like structures, which are
functionally equivalent to the alveoli
in
mammals.
The
parabronchi
extend
between
large
dorsobronchi
and
ventrobronchi,
both
of
which
are
connected to an even larger tube, the
mesobronchus.
The
parabronchi
and
connecting tubes form the lung, which is
contained within a thoracic cavity.
However, the volume of the thoracic cage
and lung changes very little during
breathing
and
therefore,
are
not
directly
involved
in
avian
lung
ventilation.
In
birds,
the
air-sac
system connected to the lungs ventilates
the avian lungs. During inspiration, air
flows through the mesobronchus into the
caudal air sacs. Air also moves through
the dorsobronchus and the parabronchi
into the cranial air sacs. Oxygen is
then diffused into the air capillaries
from the parabronchi and is taken up by
the
blood.
During
expiration,
air
leaving the caudal air sacs passes
through the parabronchi and then through
Notes in Animal Physiology by CCDivina…………
91
the mesobronchus to the trachea. The
cranial air sacs, during expiration,
move air through the ventrobronchi to
the trachea and into the environment.
The
bird
ventilation
mechanism
is
special because birds are capable of
flying
at
high
altitudes
while
maintaining a sufficient supply of O2 in
their
bodies.
Specifically,
the
unidirectional flow of air through the
parabronchi
aids
in
increasing
the
efficiency of gas exchange within the
avian
lungs
thus
giving
birds
the
capability of flying at high altitudes.
This means of gas exchange is more
efficient that thet tidal flow model
seen in mammals.
Reptiles. The ribs of reptiles form
a thoracic cage around the lungs. During
inhalation, the ribs moving cranially
and ventrally, enlarging the thoracic
cage. This process reduces the pressure
within
the
cage
below
atmospheric
pressure. The nares and glottis open and
air flows into the lungs. Exhalation
occurs passively by the relaxation of
the muscles that enlarge the thoracic
cage, which release energy stored in
stretching the elastic component of the
lung and body wall.
In tortoises and turtles, the ribs
are fused to a rigid shell. Outward
movements of the limb flanks and/or the
ventral part of the shell and by forward
movements of the shoulders are what
Notes in Animal Physiology by CCDivina…………
92
inflate the lungs. The reverse process
results in lung deflation, involving the
retraction of limbs and head into the
shell leading to a decrease in pulmonary
volume.
Therefore, when a turtle is
withdrawn into its shell, its lungs are
deflated and the turtle can't breathe.
Frogs. In frogs, the nares open
into a buccal cavity, which is connected
through the glottis to a pair of lungs.
During inhalation, air is drawn into the
buccal cavity with the nares open and
the glottis closed. Then the nares close
and the glottis is opened. The buccal
floor then rises, forcing air from the
buccal cavity into the lungs. This lungfilling process may be repeated several
times
in
sequence
inhaling
air
in
portions. This same process may also
occur during expiration in which the
lungs release air in portions. Inhaling
and exhaling air in portions may produce
a mixture of pulmonary air low in O2 and
high in CO2. This complex method of lung
ventilation
may
be
to
reduce
fluctuations in CO2 levels in the lungs
to stabilize and regulate blood PCO2 and
control blood pH.
Frogs also exchange
gasses across their skin, so the lungs
are not the only repsiratory surface.
Invertebrates. Invertebrates have a
variety of gas-transfer mechanisms. In
some invertebrates, ventilation does not
occur.
These
invertebrates
rely
on
diffusion of gases between the lung and
Notes in Animal Physiology by CCDivina…………
93
the environment. Spiders have ventilated
lungs called "book lungs". The lungs
have respiratory surfaces consisting of
thin, blood-filled plates that extend
like the leaves of a book into a body
cavity guarded by an opening (spiracle).
The spiracles open and close to regulate
the rate of water loss from these "book
lungs". Snails and slugs also have
ventilated lungs in which their lung
volume changes enabling them to emerge
from and withdraw into their rigid
shells. In aquatic snails the lungs
serve to reduce the animal’s density.
Most
insects
have
a
gas-transfer
mechanism called the tracheal system (to
know more information on the insect
tracheal system, link to the questions:
How do insect tracheals work? How are
they different from lungs and gills?)

How do gills work?
For most fish species gills work by a
unidirectional flow of water over the
epithelial surface of the gill, where
the transfer of gases is made (O2 in, CO2
out). The reason for this unidirectional
flow of water, and not an inhaling and
exhaling of water, is due to the
energetics of the system. The energy
that would be required to move water
into and out of a respiratory organ
would be much more than that used to
move air because water is more dense and
viscous.
Notes in Animal Physiology by CCDivina…………
94
The blood flowing just under the
epithelial gill tissue usually moves in
a countercurrent flow to that of the
water moving over it. This allows for
the most O2 to be taken in by the blood
because the diffusion gradient is kept
high by the blood picking up oxygen as
it moves along, but always coming in
contact with water that has a higher O2
content. The blood receiving the O2 will
continue to pick up O2 as it moves along
because fresh water is being washed over
the epithelial lining of the gills. An
important aspect to remember here is
that the water going over the gills
needs
to
be
moving
unidirectional,
either by the fish forcing the water to
move in one direction or if the water is
moving mostly in one direction.
There are two ways fish ventilate
their lungs: buccal/opercular pumping
(active ventilation) and ram ventilation
(passive ventilation). The fish pulling
in water through the mouth (buccal
chamber) and pushing it over the gills
and out of the opercular chamber (where
the
gills
are
housed)
accomplishes
buccal/opercular
ventilation.
The
pressure in the buccal chamber is kept
higher
than
the
pressure
in
the
opercular chamber so the fresh water is
constantly being flushed over the gills.
A fish swimming with its mouth open,
allowing water to wash over the gills
accomplishes
ram
ventilation.
This
method of ventilation requires fast
Notes in Animal Physiology by CCDivina…………
95
water or a fast fish to keep enough
oxygen going to the gill surface.

How do insect tracheoles work? How
are they different from lungs and
gills?
Insect tracheal systems are a series of
air filled tubes that run from the edge
of the exoskeleton to the cells/tissues
far within the body. The tracheal system
terminates at the tracheoles, that often
go in between or right into cells to
deliver
O2
very
close
to
the
mitochondria. There is usually fluid
between
the
terminal
ends
of
the
tracheols and the body cells, but as the
insect becomes more active the fluid is
replaced by air so gas exchange is
heightened. The use of tracheal systems
is superior to using water or blood as
mediums of gas exchange because O2 and
CO2 diffuse 10,000 times more rapidly in
air so the necessary gases can be
exchanged more quickly. However, there
is
a
size
limit
for
effective
ventilation via a tracheal system, which
is one reason that insects cannot grow
to gargantuan sizes.
The inner wall surface of the
tracheal system is made of the same
material that composes the exoskeleton,
which helps to prevent water loss.
Spiracles, the openings to the outside
air, can be opened and closed at will to
Notes in Animal Physiology by CCDivina…………
96
in regulate air exchange, water loss,
and to keep out debris.
Ventilation is usually accomplished
through convection, the mass movement of
gases. Some larger insects can compress
and expand their body wall to coincide
with
the
opening
and
closing
of
spiracles to pull air in and push air
out. To reduce the amount of energy used
in respiration some insects use the
discontinuous ventilation cycle (DVC)
which is composed of open, closed, and
intermediate flutter phases. During the
closed phase (spiracles closed) the O2
that is in the body is being used more
rapidly than the CO2 being produced. Due
to this, when the open phase begins
there is a O2 gradient, the low end being
within the body, forcing a rush of O2
from
the
surrounding
air
into
the
spiracles and releasing any CO2 that was
produced. This process may be helped
along by the expansion of respiratory
sacs within the body to pull more air in
or push more air out. During the flutter
phase there is rapid inhalation and
exhalation. This type of ventilation
uses the most energy and it is not
understood why it is done.

What is the role of pulmonary
surfactants in respiration?
Pulmonary
surfactants
are
lipoprotein complexes produced in the
lungs that are used to reduce the effort
Notes in Animal Physiology by CCDivina…………
97
in breathing and help prevent the
collapse
of
alveoli.
Pulmonary
surfactants
make
expansion
of
the
alveoli easier by lowering the surface
tension
that
holds
membranes
of
different alveoli together and minimizes
expansion of individual alveoli. This
makes it easier for alveoli membranes to
slide against each other when they are
expanded to take in air.
Surfactants also reduce the chances
of alveolar collapse by stabilizing
surface tension when an alveoli sac is
expanded. When alveoli are expanded the
surfactant is spread out more, which
increases
surface
tension.
Surface
tension is a major contributor to wall
tension, which determines if a small
alveolar sac collapses into a larger
alveolar sac. Collapse occurs when the
pressure inside a small alveolar sac
(wall tension in relation to the radius
of the sac) is greater that the pressure
in a larger alveolar sac, forcing the
air in a small sac (high pressure) to
force its way into the large sac (low
pressure). The surfactant prevents this
by minimizing the surface tension, which
minimizes the difference in wall tension
and thereby minimizing the
pressure
difference between alveoli.

How
are
breathing
controlled or regulated?
patterns
Notes in Animal Physiology by CCDivina…………
98
Breathing
is
an
automatic
and
rhythmic behavior regulated by several
nerve
centers
in
the
brain,
more
specifically, in the neurons of the pons
and
medulla
oblongata.
The
central
processing
of
many
sensory
inputs
control breathing movements. The central
processor is made up of a pattern
generator and a rhythm generator. From
these, the depth and amplitude of each
breath is controlled and the frequency
of
breathing
is
controlled,
respectively.
Ventilation
helps
maintain
satisfactory rates of gas transfer and
blood pH levels. Breathing movements
with eating, talking, or other bodily
functions are controlled by sensory
inputs
as
well.
The
muscles
and
diaphragm help ventilate the lungs. This
action is stimulated by the spinal motor
neurons and the phrenic nerve that get
information from the neurons that make
up the medullary respiratory centers.
The muscles of the respiratory system
are finely controlled, and this allows
humans to breathe, sing, and whistle.
The medullary respiratory center also
contains
inspiratory
and
expiratory
neurons. The activity of the inspiratory
neurons correspond to inspiration.
The
networks of neurons connect to higher
brain centers, the chemoreceptors and
mechanoreceptors.
Notes in Animal Physiology by CCDivina…………
99
Neuronal action has much to do with
breathing and respiratory activity. From
the phrenic nerve or from individual
neurons in the medulla, scientists have
been able to record inspiratory neuronal
activity and learn more. Inspiration is
characterized by a changing release of
medullary neurons. The activity recorded
shows a rapid onset, a gradual rise, and
an abrupt termination with a sudden
burst of activity related to inhalation.
Following this activity, the inspiratory
muscles
contract
and
intrapulmonary
pressure decreases. Inspiratory neuronal
activity can be said to depend on the
cycle of various neurons- inspiratory,
early
inspiratory,
off-switch,
post
inspiratory, and expiratory neurons. The
"off-switch" neurons come about at the
sharp cutoff point in the activity of
inhalation,
and
also
when
neuronal
activity has reached a threshold level.
Pulmonary stretch receptors that are
stimulated by lung expansion decrease
the
threshold
level.
Without
these
receptors working on the inspiratory
neurons, there would be over-expansion
of the lung. At the beginning of
expiration, the amount of work by the
inspiratory muscles begins to decrease,
which is caused by the post-inspiratory
neurons. The post-inspiratory neurons
are responsible for slowing the rates of
expiration. At the end of the postinspiratory
activity,
the
expiratory
neurons are then released.
Notes in Animal Physiology by CCDivina…………
100
The time between each breath is
determined by the interval between the
bursts of activity of the inspiratory
neurons. The interval between a burst of
activity is related to the amount of
activity in the burst that came before
it, as well as with nerves in the
pulmonary stretch receptors. If the
activity of inspiration is great, as is
when taking a deep breath, there is a
longer interval between inspirations.
This allows the ratio of duration on
inspiratory and expiratory activity to
stay constant no matter how long the
breath taken is. The pulmonary stretch
receptors can influence this ration,
however, depending on their activity. If
these receptors are very active, the
duration of expiration may be extended,
leaving a longer time for exhalation.
This can occur during expiration when
the lung empties out slowly and when the
pulmonary stretch receptors are still
active while the lung stays inflated.
Expiratory
neuronal
activity
appears
not
to
influence
normal
exhalation. Exhalation most often occurs
passively,
as
the
thoracic
cavity
relaxes
after
inhalation.
Expiratory
neurons are used for forced exhalation,
however, and are only active when the
inspiratory neurons are still.
The human respiratory system has
the ability to adjust its breathing
patterns to different environments and
Notes in Animal Physiology by CCDivina…………
101
to disturbances in breathing, such as
asthma (a narrowing of the airway which
causes
breathing
difficulties).
This
flexibility is due to a number of
sensors found throughout the body, which
send signals to the respiratory networks
in the brain. The chemoreceptors detect
any changes of acidity that may occur in
the cerebral spinal fluid (CSF) in the
brain, or in blood. For example, when
PCO2 levels increase in the body, the
levels of pH in the CSF decrease. The
chemoreceptors act to drive ventilation,
and
the
amount
of
breathing
is
increased. The mechanoreceptors of the
body help maintain any expansions of the
lung and also help maintain the size of
the airway.

How does an animal
extreme conditions?
respond
to
Animals have the ability to respond
to extreme conditions, such as reduced
oxygen
levels
(hypoxia),
increased
carbon
dioxide
levels
(hypercapnia),
diving, and exercise. As we will see,
each of the extremes mentioned will
induce a respiratory response specific
to its demands.
Decreased O2 levels (hypoxia)
In aquatic environments, gas mixing
and diffusion occur less rapidly than in
air. Because of this, aquatic animals
experience frequent changes in O2 levels
Notes in Animal Physiology by CCDivina…………
102
and face regions of hypoxia. CO2 levels
may or may not come about with different
O2 levels.
Some animals can survive periods of
hypoxia. To do so, the animals either
use anaerobic pathways, or will adjust
their
respiratory
and
cardiovascular
systems in order to deliver oxygen
throughout
their
bodies
while
experiencing reduced O2 availability.
In air, the levels of O2 and CO2 can
remain relatively stable. There is,
however, a decrease in O2 levels with
higher
altitudes.
With
increasing
altitude, there is a gradual reduction
in PO2, and each animal has a different
way of fighting these conditions.
For
example, and increase in blood levels
of 2,3 DPG will decrease the affinity
of Hb for O2, thereby releasing more O2
for the tissues to use.
A decrease in PO2 of the air will
cause a decrease in blood PO2. The
carotid and aortic bodies are stimulated
when this happens, causing an increase
in lung ventilation. When there is an
increase in lung ventilation there is
more CO2 eliminated and a reduction in
blood PCO2 as well. As a result, the pH
of the CSF rises and tends to reduce
ventilation. When an animal is in an
area of hypoxia for a longer period of
time, blood and CSF pH levels are
brought back down to normal by the
Notes in Animal Physiology by CCDivina…………
103
release of bicarbonate in the body. For
instance, for a human who has moved to a
higher altitude, this process takes
about one week. The carotid bodies and
the aortic body chemoreceptors may be
reset to the lower CO2 levels. Hypoxic
conditions cause a vasoconstriction in
the pulmonary capillaries and a rise in
pulmonary
blood
pressure.
This
circulates the blood away from the
poorly ventilated areas of the lung.
There are other effects to living
in such an extreme condition. Humans,
for example, tend to be smaller in size,
barrel chested, and have an increased
lung volume. There is a reduction in
limb development and often excessive
growth or development of the right
ventricle, due to increased pulmonary
blood pressures. Also, over long periods
of time, most animals will increase the
number of red blood cells and the amount
of hemoglobin in the blood. This feature
increases the oxygen capacity of the
blood. If there is a decrease in O2
levels in the blood, erythropoietin, a
hormone of the kidney and liver, is
produced. This hormone stimultes red
blood cells are production in bone
marrow. Hypoxia may also result in
systemic vasodilation, as well as an
increased
cardiac
output.
When
O2
supplies are restored from increased
hemoglobin levels in the blood and
through ventilation, cardiac output is
brought back to normal.
Notes in Animal Physiology by CCDivina…………
104
Increased CO2 levels (hypercapnia)
PCO2 represents the amount of CO2 in
solution. When there is an increase in
blood PCO2, there is an increase in
ventilation. The aortic and carotid body
chemoreceptors, the mechanoreceptors in
the lungs, and most especially, the
central
H+
receptors,
regulate
this
activity. They do so by sending messages
to the respiratory center of the brain.
The pH of the CSF is brought back to
normal
levels
in
order
to
bring
ventilation levels back to normal as
well. When there is an increase in CO2
levels, there is a distinct increase in
ventilation.
After
the
stress
of
increased
CO2
levels
is
relieved,
ventilation gradually returns to a level
slightly above the ventilation level
that occurred before hypercapnia. The
reason it returns to a level only
slightly above the initial ventilation
volume relates to a rise in plasma and
CSF bicarbonate levels. As a result of
the
increased
plasma
and
CSF
bicarbonate, pH levels are brought back
to normal, even though there may still
be a high level of CO2.
Diving by air-breathing animals
During
a
dive,
animals
are
subjected to periods of hypoxia. Anoxia,
severe
hypoxic
conditions
that
can
result in permanent damage, is a large
problem for a mammal’s central nervous
Notes in Animal Physiology by CCDivina…………
105
system (CNS) and because of this, oxygen
must be continuously supplied to the
animal.
Throughout
a
dive,
animals
combat anoxia by making use of oxygen
stores in the lungs, blood, and tissues.
Animals that dive have higher hemoglobin
levels,
which
increase
the
oxygen
capacity of the blood, and also have
larger
oxygen
stores
in
muscle
(
myoglobin ) to efficiently supply the
body with O2. In order to utilize the
stores efficiently during a dive, blood
is delivered to the brain and heart
first. The tissues and organs to where
blood did not go to resort to an
anaerobic pathway. As a result, the
heart rate slows and cardiac output
decreases. The O2 stores need to be large
enough to sustain aerobic metabolism
because diving animals cannot tolerate
the large buildup of lactic acid from
anaerobic metabolism.
During
a
dive,
inspiration
is
prevented and water is detected from
receptors found near the glottis, mouth,
or nose. Although there is an increase
in CO2 levels and a decrease in blood pH,
ventilation
is
prevented.
This
is
because the carotid and aortic body
chemoreceptors are not acted upon by the
respiratory
neurons
to
cause
ventilation.
One potential danger of a prolonged
dive is that gases in solution in the
blood under the higher pressure of
Notes in Animal Physiology by CCDivina…………
106
greater depth may come out of solution
too quickly and form air bubbles in the
blood
vessels
when
the
pressure
diminishes. In humans, this can cause a
condition known as "the bends", in which
gas bubbles accumulate in the joints,
and can even obstruct blood flow in
small vessels in the brain and other
parts of the body. Many diving mammals
prevent this condition by exhaling when
they dive, thereby emptying most of the
air out of their lungs.
In addition,
under
the
pressure
of
diving,
the
alveoli collapse, thereby forcing air
into the bronchioles, where it cannot go
into solution in the blood.
Exercise
During exercise, more oxygen is
needed, and more CO2 and metabolic acid
are produced. In addition, there is an
increased cardiac output because the
tissues need more oxygen supplied to
them. This is also caused due to an
increase of lung ventilation to support
gas tensions in arterial blood, which
experiences faster blood flow. When an
individual is exercising, the venous
blood shows signs of decreased O2 levels,
increased CO2 levels, and an increase in
H+
levels.
In
the
arterial
blood,
however, the average PO2 and PCO2 do not
differ much as they do in the venous
blood,
except
when
under
extreme
exercise. When exercise has stopped,
there is a decrease in the amount of
Notes in Animal Physiology by CCDivina…………
107
breathing and eventually, a decline in
ventilation volume as well once the
balance between O2 consumption and CO2
production is restored and the O2 needs
are met.
This may take a while, if a
significant oxygen debt has been built
up by a prolonged period of anaerobic
muscle activity.

What are some of the physiological
problems
associated
with
high
altitude?
Altitude Sickness, and the related
disorders
and
symptoms,
pose
an
immediate threat to athletes who spend
their time exercising at high altitudes.
The most commonly affected athletes are
high altitude mountain climbers. It is
not uncommon to find them above 20,000
feet
using
skill,
strength
and
concentration to scale some of the most
dangerous mountains our Earth has to
offer. Unfortunately, the challenge of
high altitude mountaineering also brings
with it the risk of serious illness and
possibly death. Why is this? Why does
our body respond so negatively to high
altitude environments?
Increased altitude is coupled with
decrease atmospheric pressure meaning
that for every breath inhaled; there is
less O2 available. Think of breathing
inside a bedroom filled with 1000 liters
of O2. There is plenty of air around you
and the pressure is high, like it is at
Notes in Animal Physiology by CCDivina…………
108
sea level. Now imagine you are breathing
in a warehouse that is filled with an
equal amount of air. The decreased in
pressure
would
make
it
harder
to
breathe. The atmospheric pressure on top
of Mt. Everest (29,028 ft) is 33% less
than it is at sea level. This means that
66% less oxygen is available. This is
what climbers face when performing at
high altitudes.
Due to the oxygen constraint, our
bodies are forced to work harder to
continue to metabolize. Respiration must
increase to get sufficient oxygen across
the lungs. Increasing our respiration
can be taxing to our systems. If the
body
overdoes
it,
Acute
Mountain
Sickness (AMS) can occur. This is the
result of increased respiration and
circulation. The body overcompensates
for the decreased oxygen by sending too
much to the brain. Leakage into the
brain
occurs
and
causes
swelling.
Decreased oxygen also starves nerve
cells,
triggering
the
release
of
adenosine. This chemical decreases the
body’s metabolism, decreasing our need
for
oxygen.
It
also
dilates
blood
vessels into the head and neck, which
allows more oxygen to go to the brain.
This is the same dilation that is
correlated with migraine headaches. A
common
treatment
for
the
migraine
symptoms is the use of caffeine.
Notes in Animal Physiology by CCDivina…………
109
Caffeine
blocks
the
adenosine
receptors,
thus
preventing
vasodilatation. If AMS goes unnoticed, a
more serious sickness can occur. High
Altitude
Cerebral
Edema
(HACE)
has
occurred from 10,000 ft. and above. It
occurs when AMS is overlooked and thus
brain swelling increases. In extreme
cases, death can result. The symptoms of
HACE are imbalance, severe headache,
vomiting, nausea, and hallucinations.
Known treatments include rapid descent,
supplemental
oxygen,
water,
and
a
diuretic called Diamox.
Victims of HACE often experience
comas and death. The increased blood
flow, as a result of high altitude that
was mentioned before, can also lead to
High Altitude Pulmonary Edema (HAPE).
This
occurs
when
excessive
blood
pressure causes fluid to leak from the
blood vessels into the alveoli sacs of
the lungs. Cases have been seen at 8,000
ft. and above and were characterized by
difficulty breathing, gurgling sound in
lungs, fever, coughing, and exhaustion.
The fluid in the lungs blocks the
oxygen-blood
interface.
The
body
compensates by increasing heart rate and
blood pressure, thereby forcing more
fluid into the lungs. Eventually, if
altitude is not decreased, the victim
drowns.
No
oxygen
reaches
the
lung/capillary interface.
Notes in Animal Physiology by CCDivina…………
110
Other problems associated with high
altitude include Periodic Breathing and
Khumbu Cough. In Periodic Breathing,
during sleep above 14,000 ft., climbers
will repeatedly stop breathing, gasp,
hyperventilate, and then stop again. The
medulla of the brain is affected causing
breathing to become irregular. CO2 builds
up, the sleeper hyperventilates, CO2
decrease, respiration stops, and the
cycle
continues.
The
body
actually
responds to a state of alkalosis, which
causes the shut off of breathing. Khumbu
Cough
is
commonly
seen
with
high
altitude climbing. It is characterized
by a dry cough that results from too
high a breathing rate. The mucosa of the
bronchi dries out due to the increased
breathing rate and contact with dry,
cold air. Besides irritation, the Khumbu
Cough can result in broken ribs as a
result of severe coughing episodes. The
only prevention is to keep the breathing
rate down. This reduces the drying out
of the mucosa.
Notes in Animal Physiology by CCDivina…………
111
Circulatory System
Transport systems functionally connect
body cells with the organs of exchange
The exchange of oxygen, carbon
dioxide, nutrients and metabolic waste
between an organism's cells and the
environment occurs across fluid-bathed
membranes. Because most of their cells
are to far from the outside environment
to be serviced by diffusion or active
transport many animals have a special
system that transports chemicals within
the body by transporting fluids ( blood
or
interstitial flidy0 through out the
body,
transport
systems
provide
a
lifeline between the aqueous environment
of living cells and the organs such as
the lungs, the exchange chemicals with
the outside environment.
The transport system also functions
in homeostasis enabling other organ
systems to regulate the chemical and
physical properties of the cellular
environment.
 Most
invertebrates
have
a
gastrovascular cavity or a circulatory
system for internal transport
Cnidarians
and
flatworms
have
gastrovascular cavities that function in
circulation
as
well
as
digestion.
Arthropods and most mollusks have
Notes in Animal Physiology by CCDivina…………
112
open
circulatory
systems,
in
which
tissues are bathed directly in hemolymph
pumped by a heart into sinuses. Annelids
and some mollusk have closed circulatory
systems with blood confined to vessels,
some of which pulsate and function s
hearts.
Diverse adaptations of a cardiovascular
system have evolved in vertebrates
In vertebrates, blood flows in a
closed cardiovascular system consisting
of blood vessels and a two-to fourchambered heart, the heart has one
atrium or two atria. Which pump blood
into arteries. Arteries branch into
arterial exchange between blood and
interstitial fluid. Capillaries rejoin
into venules that converge into veins.
In fishes, the heart has a single
atrium and single ventricle that pump
blood to gills for oxygenation
the
blood then travels to other capillary
beds of the body before returning to the
hear.
Amphibians
and most reptiles have
a three-chambered heart in which the
single-ventricle pumps blood to both
lungs and body in the pulmonary
and
systemic circuits. These two circuits
return blood to separate atria. Their
soluble
circulation
repumps
blood
returning from the capillary beds of
the respiratory organ, thus ensuring a
Notes in Animal Physiology by CCDivina…………
113
strong
flow of blood to the rest of
the body.
Birds and mammals, both endotherms,
have four
chambered hearts that keep
oxygen-rich
and
oxygen-poor
blood
completely separated.

The
Rhythmic pumping of them mammalian
heart drive blood through pulmonary
and systemic circuits.
Heart

The
cardiac
cycle
consist
of
periods
of
contraction,
called
systole and periods of relaxation
called diastole.

Heart valves dictate a one-way flow
of blood through the heart

Together with the stroke volume,
heart rate ( pulse) determines
cardiac output the volume of blood
pumped
into
the
systemic
circulation per minute.

The intrinsic contraction of the
cardiac muscle is coordinated by a
conduction system originating in
the
sino-atrial
(SA
node
(
pacemaker0
of the right atrium,
the pacemaker initiates waves of
contraction that spreads to both
atria, hesitates momentarily at the
atrioventricular (AV) node and then
Notes in Animal Physiology by CCDivina…………
114
progresses to both ventricles. The
pacemaker is
in itself influenced
by
nerves,
hormones
and
body
temperature and by atrial volume
changes during exercise.

All
blood
vessels
including
capillaries, are lined by a single
layer of endothelium, arteries and
veins have to additional outer
layers composed of characteristic
proportions
of
smooth
muscle,
elastic
fibers
and
connective
tissue.

The velocity of blood flow varies
in he circulatory system being
slowest in the capillary beds as a
result of the high resistance and
large total cross-sectional area of
the
arterioles
and
capillaries,
this
slower
flow
enhances
the
exchange of substances between the
blood and interstitial fluid.

Blood pressure is determined by
cardiac
output
and
peripheral
resistance
due
to
variable
constriction the arterioles.

Muscular
activity
and
pressure
changes
during
breathing
propel
blood back to the heart in veins
equipped with one-way valves.

The steady supple
different organs is
of blood
determined
Notes in Animal Physiology by CCDivina…………
to
by
115
variable constriction of arterioles
and capillary sphincters.

Capillary exchange is the ultimate
function of the circulatory system
substances
transverse
the
endothelium
in
endocytoticexocytotic vesicles, by diffusion
or are dissolved in fluids force
out by blood pressure are the
arterial ends of the capillary.
HEART- pulsatile, four–chamber pump
composed
of
two
atria
and
two
ventricles; Atria principal entryway to
the ventricles; Ventricles supply main
force that propels blood throughout the
lungs
and
through
the
peripheral
circulatory system
Physiology of Cardiac Muscle
3 muscles – (1) atrial muscle , (2)
ventricular muscle and
(3) specialized excitatory and
conductive muscle fibers
atrial
and
ventricular
type
contract
same
as
skeletal
muscle
fibers
Excitatory
muscle
provide
excitatory system and transmission
system
for
rapid
conduction
of
impulses throughout the heart
Cardiac muscle as a functional
syncitium,
intercalated
discs
–
membranes that separate individual
cardiac
muscle
cells
flow
with
relative ease along
the axes of the
Notes in Animal Physiology by CCDivina…………
116
cardiac muscle fibers so that action
potentials
travel
from
past
the
intercalated disc without hindrance in syncitium
2 syncitia – atrial and ventricular
syncitia
Conductive
sytem
A-V
bundle
conductive system for both atria and
ventricle
All or Nothing Principle Applied to the
Heart
Stimulation of any single
muscle
fiber
causes
the
potential to travel over the
muscles mass
atrial
action
entire
Role of Calcium
Action potential travels over the
muscle fiber membrane causing action
potential to travel into the interior
of the fiber through T tubules. T
tubules causes the calcium ions to be
released
into
the
muscle
fiber
sarcoplasm from the cisternae of the
sarcoplasmic
retiluculum.
Ca
ions
diffuse rapidly onto myofibrils and
chemical reaction promote the sliding
of the actin and myosin filaments
along each other- muscle contraction.
Immediately after the calcium ions
are
transported
back
into
the
sarcoplasmic reticulum or into the
t tubules -muscle relaxes.
Notes in Animal Physiology by CCDivina…………
117
The Cardiac Cycle
period
from
one
end
of
heart
contraction to the end of the next is
the cardiac cycle
each
cycle
is
initiated
by
spontaneous generation of an action
potential in the S-A node. located in
the posterior wall of the right atrium
near the opening of the superior vena
cava and the action potential travels
rapidly through both atria and thence
through the A-V bundle, onto the
ventricles
The atria acts as primer pump
for
the ventricle, and ventricle provide
the major source of power for moving
blood through the vascular system
Systole and Diastole.
Diastole period of relaxation
Systole – period of contraction.
Functions of the Valves
The Atrioventricular Valves.
A-V
valves
(tricuspid
and
mitral
valves) prevent backflow of blood from
the ventricle to
the atria and seminal
valve (aortic and pulmonary valves )
prevent backflow from the aorta and
pulmonary arteries into the ventricle
during diastole.
The valves closes when a backward
pressure gradient pushes blood backward
and they open when a forward pressure
Notes in Animal Physiology by CCDivina…………
118
gradient forces blood in the forward
direction .
Papillary muscles attach to the vanes
of the A-V valves by the chordae
tendineae. Papillary muscles contract
when the ventricular walls contract, the
pull the vanes of the valves inward
toward the ventricle to prevent the
bulging too far backward toward the
atria during ventricular contraction
Aortic and pulmonary valves. The high
pressures in the arteries at the end of
systole caused the seminar valves to
snap to the close position in comparison
with a much sought closure of the A-V
valves.
The velocity of blood passing through
the aortic and pulmonary valves is far
grater than the through the AV valves
Regulation of Cardiac Function
When at rest, the heart pumps only
4 to 6 liters of blood each minute,
however during severe exercise it may be
required to pump as much as 5x this
amount
Two ways of regulation:
1.
Intrinsic auto regulation in
response to changes in volume
of blood flowing into the
heart
2.
Reflex
control of the heart
by
the
autonomic
nervous
system.
Intrinsic auto regulation of cardiac
pumping –
Notes in Animal Physiology by CCDivina…………
119
Frank Starling Law of the heart
The greater the heart is filled
during diastole, the greater will be the
quantity of blood pumped into the aorta
within physiological limits, the heart
pumps all the blood that comes to it
without allowing
extensive damming of
blood in the veins.
When
cardiac
muscle
becomes
stretched in an extra amount, when extra
amount
of
blood
enters
the
heart
chamber, the unusually stretched muscle
contracts
with
a
greatly
increased
force, thereby automatically pumping the
extra blood into the arteries
Control by Nerves
The nerves
1. Change the heart rate
2. Change
the
strength
of
contraction of the heart and
3. Parasympathetic
stimulation
decreases
heart
rate
and
sympathetic
stimulation
increases heart
Some Factors Affecting Rate of Heart
Beat
1. Exercise. Exercise over
a period of
many weeks lead to hypertrophy of the
cardiac muscles
and enlargement of
the ventricular chambers – enhanced
strength of heart
Notes in Animal Physiology by CCDivina…………
120
2. Excess
potassium
ions
in
extracellular fluid causes the heart
to
become
extremely
dilated
and
flaccid and slow the heart rate. Very
large quantities can block conduction
of the cardiac impulse from the atria
to ventricles through the A-V bundle –
weaker contraction
3. Excess calcium ions causes effect
almost exactly opposite to potassium –
spastic action
4. Sodium ions decreases cardiac function
similar to potassium. sodium ions
compete with calcium ions
Rhytmic excitation of the heart
The heart is endowed with special
system
for
generating
rhythmical
impulses to cause rhythmical contraction
of the heart muscle and for conducting
these impulses throughout the heart. The
adult human heart normally contracts at
72 beats per minute.
Special
excitatory
conductive
systems
of
the
heart
that
control
cardiac contractions
1.
S-A
node,
normal
rhythmic
self-excitatory
impulse
is
generated
2.
A-V node, in which the impulse
from the atria is delayed
before
passing
into
the
ventricles
Notes in Animal Physiology by CCDivina…………
121
3.
4.
The A-V bundle, which conducts
impulse from heart atria into
the ventricles
The left and right bundles of
Purkinje
fibersconduct
cardiac impulse to all parts
of the ventricles.
SA NODE
Small
crescent
shape
strip
of
specialized muscle in posterior wall of
the right atrium immediately beneath
median opening of the superior vena cava
S-A node controls the rate of heat beat
of the entire heart
The membranes of the S-A fibers are
very permeable to sodium, therefore,
large numbers of sodium ions leak to the
interior of the
fiber, causing the
resting membrane potential
to drift
continually towards a more positive
value. Just as soon as the membrane
potential reaches threshold level for
discharge, an action potential occurs.
At the end of the action potential, the
membrane become highly permeable to
potassium ions and leakage of potassium
ions out of the fiber carries positive
charges outside, therefore, the inside
membrane
potential
now
become
more
negative than ever because of loss of
positive
charge
causing
hyperpolarization.
This
condition
persist for a fraction of a second and
then
disappears
when
the
natural
leakiness of the membrane to sodium ions
elicits another action potential.
Notes in Animal Physiology by CCDivina…………
122
Arteries , Veins and
Capillaries
The rate of blood flow in any spot in
circulatory systems depends on the total
cross-sectional area of the vessels.
The aorta and venae cavae have smaller
cross sectional area in the comprasion
to
the
arterioles,
capillaries
and
venules added together.
The rate of blood flow is therefore
faster in the aorta and venae cavae and
slowest in the capillaries.
As blood leaves the
capillaries and
passes into veins, the total crosssectional area through which it flows is
reduced, so that rate of blood flow
accelerates even the blood pressure
remains loss.
Regulation
Vessels
of
Blood
flow
through
the
The amount of blood flowing into a
given capillary bed or into the veins is
also under the direct control of nervous
systems
Vasoconstriciton – contraction of the
precapillary sphincters and the walls of
the
vessels
in
response
to
nerve
impulses
Vasoconstriction helps stabilize blood
flow during a change in body position
such as standing up after lying in bed.
Capillaries open in response to local
tissue
needs.
The
opening
is
vasodilation
Notes in Animal Physiology by CCDivina…………
123
Blood is a connective tissue with cells
suspended in plasma.
Whole blood consist so of cellular
elements (cells and pieces of cells 0
suspended in a liquid matrix called
plasma.
Plasma is a complex aqueous
solution
of
inorganic
electrolytes,
proteins,
nutrients,
metabolic
waste
products,
respiratory
gases
and
hormones.
Plasma
proteins,
influence
blood
pH
,
osmotic
pressure,
and
viscosity,
and
function
in
lipid
transport, immunity ( antibodies and
blood clotting ( fibrinogens).
Red
blood cells or erythrocyte transport
oxygen a function reflected in their
small size, biconcave shape, anaerobic
metabolism
and
hemoglobin
content.
Pluripotent stem cells in the red bone
marrow give rise to all
type of blood
cells.
Notes in Animal Physiology by CCDivina…………
124
Erthyrocytes (RBC)
A. General points
1. Life span of 120-130 days
2.
Number
present:
Male:
5
x
106/mm3 Female: 4.5 x 106/mm3
3. RBCs are 500-1000 times more
numerous than leukocytes
B. Morphological features
1. Biconcave disk with a diameter of
7-8 um and width of 2 um. The
shape
is
dependent
on
the
spectrin-ankyrin-actin
interaction.
2. Lacks a nucleus in mammals, but
nucleated in other forms (birds,
etc.)
3. Lacks
a
Golgi,
centrioles,
lysosomes, RER
4. Very few or no mitochondria ,
resulting in anaerobic glycolysis
and pentose phosphate pathways
being
important
for
energy
production.
5. Cytoplasm composed of:
a.
water
65%
b.
organelles - 1%
c. hemoglobin 34%
C. Function : transport of O2 and CO2
Five types of white blood cells or
leucocytes,
function
in
defense
by
phagocytosis of bacteria and debris or
by producing antibodies.
Leukocytes (WBCs)
Notes in Animal Physiology by CCDivina…………
125
A.
Involved
in
both
the
cellular
and
humoral defenses of the organism.
B. Morphological features
1. Granulocytes/polymorphonuclear
a. have specific granules in the
cytoplasm
b. non-mitotic cells in the blood
stream and after leaving the vascular
system
c.
three
types:
neutrophils,
eosinophils basophils
2. Agranulocytes/mononuclear
a.
lack specific granules in the
cytoplasm
b.
differ from granulocytes in that
they can reproduce by mitosis
after leaving the vascular system
c.
two
types:
lymphocytes
and
monocytes
1.
Neutrophils
(Polymorphonuclear
neutrophils, polys, PMNs, polymorphs)
A. General points
1.
Notes in Animal Physiology by CCDivina…………
126
Characterized by many lobed nucleus
and specific granules in cytoplasm
2. Comprise 50-70% of differential
count
3. 4,400/mm3
B. Morphological features
1. Diameter of 10 to 15 um
2.
Nucleus
generally
segmented,
consisting of 2 to 5 lobes held together
by chromatin; young or immature cells
are non-segmented (band or stab); may
comprise 1% of cells
3. Cytoplasm - very little RER,
Golgi,
free
ribosomes,
and
few
mitochondria ;
three types of granules
(formed by the Golgi apparatus): 50-200
granules/cell
C. Functions
1. Neutrophils serve as a first
line
of
cellular
defense
against
invasion of microorganisms. PMNs are
chemotactically attracted by devitalized
tissue, bacteria, and other foreign
bodies and factors produced by antigenantibody interactions with certain blood
proteins (complement) and they migrate
to the site of infection
2. Killing of bacteria is thus
accomplished
via
two
different
mechanisms:
a.
enzymatic
(via
fusion
of
specific
and
azurophilic
granule
contents
with
the
phagosome)
which
involves:
(1) phagocytosis
of
the
foreign
material,
thus
forming
a
phagosome,
Notes in Animal Physiology by CCDivina…………
127
(2) the specific granules fusing
with the phagosome, inactivating
the material,
(3) the azurophilic granules fusing
with the phagosome, digesting
the material, and
(4) finally the digested material
expelled from the cell.
b. via formation of reactive oxygen
compounds within the phagosome
3. Neutrophils die and become the pus
of an abscess.
4. Not all bacteria destroyed by
neutrophils. For example, the
tubercle
bacillus
survives
phagocytosis by the PMN, and must
be contained by the macrophage
which
is
derived
from
the
monocyte
Eosinophil (polymorphonuclear
eosinophil)
A. General points
1.
Characterized
by
its
large
eosinophilic
granules
in
the
cytoplasm
2. Comprise 1-4% of the differential
count
3. 200/mm3
B. Morphological features
1. Diameter of 12 to 17 um
2. Nucleus
generally consists of two
lobes held together by a strand of
chromatin; more than two lobes is
not common
Cytoplasm has lysosomes and contain
hydrolytic enzymes and peroxidase;
Notes in Animal Physiology by CCDivina…………
128
contents help in the destruction of
parasitic worms and in the hydrolysis
of
antigen-antibody
complexes
internalized by the eosinophils
C. Functions
1. Eosinophils leave the vascular
system
by
diapedesis,
and
locate
especially in the connective tissue
beneath
the
epithelium
of
the
respiratory
and
gastro-intestinal
tract.
a.
binding
of
histamine,
leukotrienes,
and
esoinophil
chemotactic factor (released by
mast
cells,
basophils,
and
neutrophils) to eosinophil plasma
membrane receptors results in the
migration of the eosinophils to
the
site
of
the
allergic
reaction, inflammatory reaction,
or parasitic worm invasion
2.
The
differential
count
of
eosinophils
increases
with
parasitic
infections
(trichinosis,
schistosomiasis,
ascaris)
a.
major
basic
protein
and
eosinophil cationic protein bore
holes
in
the
pellicles
of
parasitic
worms,
facilitating
access
of
reactive
oxygen
compounds
(e.g.
superoxides;
hydrogen
peroxide)
to
the
parasite
Notes in Animal Physiology by CCDivina…………
129
3.
4.
5.
Differential count increases in
allergic conditions such as hay
fever and asthma.
Cells
play
a
role
in
the
phagocytosis and hydrolysis of
antigen-antibody complexes.
Eosinophils
degrade
chemical
mediators such as leukotrienes
and histamine released by mast
cells
and
basophils,
thus
regulating
local
inflammatory
responses
Basophil (Polymorphonuclear
basophil)
A. General points
1.
Comprise
about
0.5%
of
differential count
2. 40/mm3
B. Morphological features
1. Diameter of 8 to 12 um
2. Nucleus ; irregular shape, does
not appear to be lobated
C. Functions
1. Increase in number along with other
leukocytes with leukemia.
2. Increase in number in smallpox,
chicken
pox,
and
sinus
inflammations.
3. Functions are appear to be involved
in
mediating
allergic
and
inflammatory reactions (functions
are similar to mast cells)
a. antigens can bind to IgE molecules
whose
Fc
portion
is
bound
to
Fc
receptors on the basophil surface; this
may cause the basophils to release the
Notes in Animal Physiology by CCDivina…………
130
specific
granule
contents
into
the
extracellular spaces
(1) release of histamine causes
smooth muscle contraction (in the
bronchial tree), vasodilation of
the microvasculature, and leaking
of blood vessels
b.
begin
to
produce
and
release
leukotrienes
(1) similar effects to histamine,
but actions are slower and more
persistent
4. Lymphocytes
A. General points
1. Produced in lymphatic nodules,
lymph
nodes,
spleen,
thymus,
tonsils, and bone marrow, and
endow
the
body
with
its
immunological defense.
2. Comprise 20-40% of differential
count
3. 2,500/mm3
B.Subdivision of small lymphocytes based
on their function, not on morphologic
features.
1. B-lymphocytes
a. compose about 15% of circulating
lymphocytes
b. called B-cells because in chick
develop in bursa of Fabricius
c.
in
humans
develop
in
bursa
equivalent (gut) or bone marrow
d. cells may leave the circulation and
enter lymphatic tissue where by
Notes in Animal Physiology by CCDivina…………
131
the process of mitosis they give
rise to clones of B-cells
e. function or fate of B-lymphocytes:
(1)Plasma cells - produce antigenspecific
circulating
immunoglobins (humoral antibody
response)
(2) Memory cells - found in lymphatic
tissue and stimulated by reexposure to antigen; reaction
termed the secondary response
2. T-lymphocytes
a.
compose
80-90%
of
circulating
lymphocytes
b. originate embryological from the
yolk sac and seed the thymus by
way of the liver and bone marrow
c. multiply and differentiate into Tlymphocytes in the thymus - each
developing lymphocyte develops an
individual antigenic specificity.
d. activation of T-cells (needed for
activation)
(1) appropriate antigen
(2) macrophages must process the
antigen for presentation
e. subsets of T-lymphocytes
(1) Cytotoxic T cells
(2) T helper cells
(3) T suppressor cells
f. function of T-lymphocytes : cell
mediated
immunity;
assist
in
humoral immunity
Notes in Animal Physiology by CCDivina…………
132
5. Monocyte
A. General points
1. Characterized partly by its large
size
2. Comprise 2-8% of the differential
count
4. 300/mm3
5. Cells originate in the bone marrow
B. Morphological features
1. Diameter of 12 to 20 um
2. Nucleus
a.
eccentrically placed and may
be oval, indented, kidney or
horseshoe shaped
b.
chromatin less condensed than
in lymphocyte, and therefore,
nucleus in lighter staining
C. Functions
1. Monocytes
exhibit
diapedesis
(continually extend and withdraw
pseudopodia)
and
reach
full
development
outside
the
blood
stream where they are known as
macrophages. Macrophages fuse to
form foreign body giant cells and
osteoclasts;
In
the
CNS
the
macrophages form microglia; in the
liver, Kupffer cells; and in the
lungs, alveolar macrophages.
2. Serve as the second line of defense
against invading organisms. Found
in areas of chronic inflammation.
3. After leaving the vascular system,
the macrophage (monocyte) plays a
role along with the T-lymphocyte in
the
differentiation
of
the
BNotes in Animal Physiology by CCDivina…………
133
lymphocyte into the plasma cell,
which produces immunoglobulins.
4. Some macrophages are particularly
good at processing and presenting
antigen and are called antigen
presenting cells
5. Monocytosis - increased monocyte
count
due
to
infectious
and
inflammatory
diseases,
tuberculosis, and leukemia.
Platelets
Platelets are fragments of cells
produced
in
the
bone
marrow
that
function
blood clotting , a cascade of
complex reactions that converted the
plasma fibrinogen to fibrin.
1. Thrombocytopenia - a deficiency in
platelets (<60,000/mm3). May occur with
certain viral diseases.
2. Role in clot formation:
a. With
trauma,
platelets
release
seratonin which causes contraction
of vascular smooth muscle, reducing
blood loss.
b. When
vessel
ruptures,
platelets
agglutinate, forming a plug which
helps close the gap
c. Platelets
release
the
enzyme
thromboplastin
3. Functions in the maintenance of
endothelial
cells
with
thrombocytopenia, blood vessels loose
their competence and blood seeps out
Notes in Animal Physiology by CCDivina…………
134
into the tissue, resulting in the
condition of thrombocytopenia purpura.
Cardiovascular disease are the leading
cause of death
A
leading
cause
of
death
is
cardiovascular disease, a deterioration
of
the
heart
and
blood
vessels.
Gradually
plaque
build
up
during
artherosclerosis
or
arteriosclerosis
narrows the diameter of blood vessel and
may be associated with vessel blockage
and consequent heart attack of stroke.
Commonly Asked Questions

What are the
advantages
of
a
closed, as compared with an open,
circulatory system?
Two
basic
types
of
transport
systems – the open and the closed
circulatory systems- occur in the larger
invertebrate animals. Smaller animal do
not need transport systems, for all of
their body cells are near internal
cavities or the external environ, In an
open circulatory system, the blood is
not
completely
enclosed
with
the
vessels, the hearts pump blood through
arteries into large cavities or sinuses,
where it mixes wit interstitial fluid
and bathes the cells of the body. The
blood is slowly return to the heart
through small pores, called ostia. And
Notes in Animal Physiology by CCDivina…………
135
bathes the cell of the body. The blood
is slowly returned to the heart s
through small pores called ostia. In a
closed circulatory system, the blood
remain
within
a
completely
enclose
system o f vessel and never comes in a
direct contact with the body cells
Material move between the blood and
interstitial fluid through the thin
walls of capillaries.
Circulation is slower in an open
system, because with some of the blood
pooled in sinuses, the hearts cannot
build up enough pressure to make the
blood flow rapidly. In an open system
cannot achieve high rates of oxygen
transport that active animals requires
animals with open system are either
quite small and sluggish of use the open
system only for transport of food and
wastes and use a different system for
transport of gases. Insects for opens
system only transport of food and wastes
and use a different system for transport
of gases, Insects of example, have a
separate system of vessels- the tracheal
system – for gas transport, the insects
circulatory system is composed of five
muscular hearts which slowly pump the
blood, which contains food and wastes
(except carbon dioxide, hominess and
other
material
though
a
system
of
vessels and open cavities in a forward
and downward direction. the blood bathes
the cells of he body in open cavities
below
the
vessel.
Providing
the
Notes in Animal Physiology by CCDivina…………
136
necessary materials (except oxygen) for
cellular
activities
and
accumulating
waste products 8 except carbon dioxide
from the cells. The blood then moves
slowly form these cavities backward and
upward to the hearts. Transport is
accelerated during physical activity,
when the skeletal l muscles contact
rhythmically, squeeze the cavities and
forcing
the
blood
back
toward
the
hearts.
Invertebrate animals that have open
circulatory
systems
include
the
arthropod (such as insects, spiders,
crabs and lobsters, and most mollusks
(such as snails, oysters and clams.
Invertebrates with a closed circulatory
system include the annelids such as
earthworms and some mollusks (such as
squids)
.
 How can a frog or a lizard be very
active if its oxygen-rich blood
mixes with oxygen-poor blood before
becoming available to the body
cells?
A frog or a lizard has a single
ventricle, which receives oxygen-poor
oxygen –poor blood from the body as well
as oxygen-rich blood form the lungs, and
in the case of a frog, from the skin.
Blood from the ventricle is pumped via
one artery to the lungs (and skin, in
the case of a frog) and via another
artery to the rest of the body. In
Notes in Animal Physiology by CCDivina…………
137
neither animal, however, is there’s
complete mixing of the two types of
blood in the ventricle, a frog has ridge
of hear tissue hat partially segregates
the ventricle into a left and right
side. The
ridge divert unoxygenated
blood fro the right atrium to he artery
leading t the lungs and skin and
oxygenated blood from the left atrium to
the artery leading to the rest of the
body. A lizard has septum, or wall, in
its ventricle that perform the same
function, but perform it much better
that the ridge in frog’s ventricle. The
septum almost completely separates the
ventricle into a left and right side
there is a very; little mixing of
oxygenated and unoxygenated blood in a
lizard
heart. The active cells of both
a frog and a lizard receive highly
oxygenated ventricles. A bird or mamma,
however, has a greater need for oxygen,
because of the high metabolic demands of
endothermy,

What controls heart rate?
The rate at which the heart muscles
contract is regulated in several ways,
the main controls is the sino-atrial
node or pacemaker, which’s a small piece
of specialized hat muscle located in the
wall of the right atrium. Electrical
impulses emitted at regular interval by
this tissue stimulate muscle contraction
the four chambers of the heart. Each
impulse travels through both atria,
Notes in Animal Physiology by CCDivina…………
138
causing
them
to
contract
almost
simultaneously,
and
on
to
another
specialized
region
–
the
atrioventricular node – which transmits the
impulse
to
both
ventricles
simultaneously, the slight delay in the
signal produces a sequence of contrition
first the two aria, the then two
ventricle.
A second regulator of heart rate is
an area within the medulla oblongata of
the rain. The cardio-inhibitory center
in this area communicates with the Sino
trial node via the vagus nerves, which
contain
both
afferent
and
efferent
axons. The afferent nerve axons, which
originate in the node and terminate in
the cardio-inhibitory center and extend
to the sinoatrial node, can time the
node to decrease the rate of heartmuscle
contractions.
The
cardioinhibitory center functions to restrains
the Sino Arial node, to hold the heart
rate in check.
In addition to feedback from the
sinoatrial mode, the cardio-inhibitory
center receiver information from sensory
surfaces
and
higher
brain
centers.
Sensory
cells
on
the
internal
and
external
body
surfaces
transmit
information t the center about such
conditions as indigestion, inhalation of
irritating
fumes
sudden
cold
temperatures and blood pressure, when
the center receiver the information, it
Notes in Animal Physiology by CCDivina…………
139
stimulates the efferent axons of the
vagus nerves, which diminish the heart
rate certain emotional l state also
stimulate the cardio-inhibitory centers,
many areas of the brain are involved in
the regulation of emotion, but the
critical pathway that influences heat
rate form the limbic system to the
cardio-inhibitory center.
The cardio-accelerating with the
medulla
oblongata
of
the
brain
is
stimulated by many factors; including
the pain sensations form the skin and
anticipation
of
exercise.
Efferent
neurons
form
the
cardio-accelerating
center terminate in the heart muscle
themselves,
rather
than
in
the
sinotarial node.
When the stimulated,
these neurons release a neurotransmitter
(norephineprine) that increase both the
heart rate and the stroke volume (amount
of blood pumped with each contraction
Hormones also affect the heart
rate. Thyroxin, the hormone secreted by
thyroid gland, increases the heart rate,
Epinephrine. A hormone secreted by the
adrenal medullas, increases both the
rate and the stroke volume.

rate
What regulates
flows
though
system.
the rate a blood
the
circulatory
Animals must be able to adjust the
of blood flown in response to
Notes in Animal Physiology by CCDivina…………
140
changing
conditions
when
cellular
activity is low, as during sleep, the ea
of blood flow is lowered to conserve
energy. During strenuous activity, the
rate of blood flow must b e rapid enough
to
meet
the
increased
demand
for
exchange of material between the bloods
and more active cells.
The cardiac output, or quantity of
blood the heart pumps per minute, is
about 5-liter sin a resting human.
Cardiac outputs is the product of two
factors, - the heart rate (number of
contractions per minute) and Stroke
volume (amount of blood ejected from the
heart during each contraction)
Heart rate is controlled primarily
by Sino Arial node, but also by cardioinhibitory
and
cardio-accelerating
center within the medulla oblongata of
the brain and by hormones secreted by
the thyroid and adrenal glands.
Stroke volume is controlled by
artery diameter. Because the vessels and
the heart form a closed circulatory
system, net volume of blood expelled
form the heart during each contraction
can only be increase if the rate at
which blood is returned to the heart
undergoes a corresponding increase. As
the volume of blood returning per minute
to the heart increases, the muscles
conditions that force blood through the
heart
becomes
stronger.
Blood
is
Notes in Animal Physiology by CCDivina…………
141
returned other heart more rapidly when
the blood pressure is higher i.e. when
arteries are more constricted.
Artery diameter is controlled by
vasomotor
center
in
the
medulla
oblongata in response to carbon dioxide
levels in the blood and by brain centers
that
control
emotions
Higher
concentrations of carbon dioxide, a
waste product of cellular respiration,
reflect
high
levels
of
cellular
activity, the amount of carbon dioxide
in the blood detected by neurons in two
vasomotor center, one on each side of
the
medulla
oblongata,
which
send
electrical-chemical
impulses
along
vasomotor nerves to the muscles of the
arties. High levels of carbon dioxide
cause
constriction
of
the
arterial
walls, and thus and increase in blood
pressure and amore rapid flow of blood
thorough the circulatory system. Low
levels of carbon dioxide product the
opposite effect: the arteries become
dilated blood pressure drops, and blood
flow becomes slower.
Finally blood flow is controlled by
the
brain
center
that
control
the
emotions, including the cerebral cortex
in
the
limbic
system,
which
emits
electrochemical impulses that travel to
the vasomotor center of ht medulla
oblongata, Certain emotional states can
accelerate the heart rate and constrict
the arteries, other emotion stress can
Notes in Animal Physiology by CCDivina…………
142
inhibit the heart rate and dilate the
arteries to though the point that the
individual faints, Information is I
transmitted from the vasomotor center to
the
arterial
walls,
which
either
constricts of dilates vessels.
Applications
1. The ECG
As
the
heart
goes
through
its
contraction-relaxation cycle, waves of
depolarization and repolarization pass
from
the
atria
to
the
ventricular
tissue. These waves produce a measurable
electrical
current
and
associated
voltage changes. Since alterations in
heart function due to disease are often
reflected
units
electrical
activity
patterns, analysis of the patterns has
considerable diagnostic use.
The instrument used to measure
heart electrical activity is called an
electrocardiogram, where electrodes are
attached to the body. These lead to an
amplifier where the tiny voltages are
magnified and fed into a recorder. An
example of a normal tracing is shown in
the figure. There are five distinct
alterations in voltage, called P,Q,R,S
and T for reference. Notice that the
measured
voltages
are
very
small,
approximately a thousandth of a volt. In
the heart the voltage changes are nearly
a
hundred
times
larger,
but
the
electrocardiograph can only measure the
Notes in Animal Physiology by CCDivina…………
143
voltages that reach the surface of the
body.
The first small change, the P wave
is produced when the atria depolarize,
the depolarization wave travels to the
ventricle where a much larger change
occurs, called the QRS region. The final
T wave is produced by the repolarization
of the ventricles. Now, compare the
normal tracing with the one made form a
fibrillating heart. Fibrillation occurs
when the heart muscle contractions are
irregular and uncoordinated and often
sets in after a severe heart attack. In
fact, fibrillation is the usual cause of
death. The ECG clearly shows the random
patterns
associated
with
the
fibrillating heart. Of course, this is
an extreme case, the ECG is more often
used to diagnose heart disease sickness
subtle changes in the ECG pattern can be
related to specific kinds of heart
damage form disease.
An example of such an abnormal
patter in is called an atrioventricular
block and results when the tissue that
normally conducts the electrical waves
from the atria to the ventricles is
damaged by disease to the extent that
conduction is impaired. In a block leak,
there is no coordination of contraction
between atrial and ventricles and the
heart’s efficiency as a pump is greatly
impaired.
Notes in Animal Physiology by CCDivina…………
144

The Pacemaker
Artificial pacemakers. As we age, the
heart may lose control of its beat, the
most common cause of this condition is
that conduction between the atria and
ventricles is blocked. The atrium may
contract normally at 70 to 80 times per
minute, driven by the pacemaker tissue,
but the ventricles beat at their own
rate at 40 to 50 times per minute.
In many instances, it is possible to
implant an artificial
pacemaker near
the heart. this is a device that
delivers a small electrical shock to the
heart at timed intervals, the purpose of
the shock is not so much to initiate
heart beat as to
coordinate the atrial
and
ventricular
contractions.
For
instance,
the pacemaker can be set so
that
it
produces
ventricular
contractions.
For
instance,
the
pacemaker can be set so that it produces
a ventricular contraction whenever the
atria contract.
A relates application of our knowledge
is the defibrillator, now found in most
hospitals, during fibrillation, waves of
contraction are moving randomly in heart
muscle and the problem is to coordinate
them. The defibrillator does this by
sending a single strong electrical shock
through the chest wall into the heart.
the heart muscle responds by contracting
completely, then often begins to beat
Notes in Animal Physiology by CCDivina…………
145
normally under the
pacemaker tissue.

influenced
of
its
Sphygmomanometers.
Blood
pressure
is
an
important
indicator of vascular function and most
of us have had our blood pressure
measures. The instrument is called a
sphygmomanometer, and consists of an
inflatable cuff that is calibrated so
that a air pressure in the cuff reads
out in millimeters of mercury to operate
the devise, the cuff is wrapped around
the upper arm while a stethoscope is
placed at the inner elbow near the
artery that supplied blood to the heart.
As the cuff is inflated, the blood
pressure in the artery is overcome so
that the artery collapses. Pressure
through the artery in spurts. At this
point , a thumping is heard in the
stethoscope as the artery fills and
collapses this is a good estimate of
systolic blood pressure. More pressure
is then released and at a second point
the thumping sound disappears when the
artery stays open even during diastole.
This
pressure is equivalent to the
diastolic blood pressure.
Notes in Animal Physiology by CCDivina…………
146
THE EXCRETORY SYSTEM
Cells
produce water and carbon
dioxide as by-products of metabolic
breakdown of sugars, fats, and proteins.
Chemical
groups
such
as
nitrogen,
sulfur,
and
phosphorous
must
be
stripped, from the large molecules to
which they were formerly attached, as
part
of
preparing
them
for
energy
conversion. The continuous production of
metabolic wastes establishes a steep
concentration gradient across the plasma
membrane, causing wastes to diffuse out
of cells and into the extracellular
fluid.
Single-celled organisms have most
of their wastes diffuse out into the
outside
environment.
Multicellular
organisms, and animals in particular,
must have a specialized organ system to
concentrate and remove wastes from the
interstitial
fluid
into
the
blood
capillaries and eventually deposit that
material at a collection point for
removal entirely from the body.
As animals perform their various
metabolic processes, protein and nucleic
acid, both of which contain nitrogen,
are broken down. While some of the
nitrogen is used to manufacture new
nitrogen-containing molecules, much of
it cannot be used for this purpose and
must be disposed of as waste. Typically,
the first nitrogen-containing molecule
Notes in Animal Physiology by CCDivina…………
147
that forms is ammonia (NH3, which is
very water-soluble, forming NH4OH, a
strong base. In some way, this ammonia
must be gotten rid of before it raises
the pH of the body fluids. Because
ammonia is so water-soluble, aquatic
animals often can get rid of it just by
diffusion into the surrounding water.
However, ammonia doesn’t readily go from
body fluids into air, so terrestrial
animals need other ways of getting rid
of nitrogenous wastes.
The two most common substances used
by terrestrial animals to get rid of
excess nitrogen are urea and uric acid.
Many animal species that aren’t terribly
concerned about water-loss, including
humans, convert the ammonia to urea,
which is water-soluble and excreted in a
water-based solution. Other organisms
such as birds, insects, or lizards,
especially if they live in an arid area,
must conserve water whenever possible,
thus convert the NH3 to uric acid. Uric
acid is not water-soluble, thus can be
excreted with little, if any, water with
it. This is the white goo in bird
droppings. While the major portion of
human nitrogenous waste is in the form
of urea, humans typically excrete some
uric acid, too. Uric acid is another
kind of purine like the adenine and
guanine in our DNA
Regulation of Extracellular Fluids
Notes in Animal Physiology by CCDivina…………
148
Excretory
systems
regulate
the
chemical composition of body fluids by
removing metabolic wastes and retaining
the proper amounts of water, salts, and
nutrients. Components of this system in
vertebrates include the kidneys, liver,
lungs, and skin.
Not all animals use the same routes
or excrete their wastes the same way
humans
do.
Excretion
applies
to
metabolic waste products that cross a
plasma membrane. Elimination is the
removal of feces.
Nitrogen Wastes
Nitrogen wastes are a by-product of
protein metabolism. Amino groups are
removed from amino acids prior to energy
conversion.
The
NH2
(amino
group)
combines with a hydrogen ion (proton) to
form ammonia (NH3).
Ammonia is very toxic and usually
is excreted directly by marine animals.
Terrestrial animals usually need to
conserve water. Ammonia is converted to
urea, a compound the body can tolerate
at higher concentrations than ammonia.
Birds and insects secrete uric acid that
they
make
through
large
energy
expenditure
but
little
water
loss.
Amphibians and mammals secrete urea that
they form in their liver. Amino groups
are turned into ammonia, which in turn
is converted to urea, dumped into the
blood and concentrated by the kidneys.
Notes in Animal Physiology by CCDivina…………
149
Water and Salt Balance
The excretory system is responsible
for regulating water balance in various
body fluids. Osmoregulation refers to
the state aquatic animals are in: they
are surrounded by freshwater and must
constantly deal with the influx of
water. Animals, such as crabs, have an
internal salt concentration very similar
to that of the surrounding ocean. Such
animals are known as osmoconformers, as
there is little water transport between
the inside of the animal and the
isotonic outside environment.
Marine vertebrates, however, have
internal concentrations of salt that are
about
one-third
of
the
surrounding
seawater.
They
are
said
to
be
osmoregulators. Osmoregulators face two
problems: prevention of water loss from
the
body
and
prevention
of
salts
diffusing into the body. Fish deal with
this by passing water out of their
tissues through their gills by osmosis
and salt through their gills by active
transport. Cartilaginous fish have a
greater
salt
concentration
than
seawater, causing water to move into the
shark by osmosis; this water is used for
excretion. Freshwater fish must prevent
water gain and salt loss. They do not
drink water, and have their skin covered
by a thin mucus. Water enters and leaves
through the gills and the fish excretory
Notes in Animal Physiology by CCDivina…………
150
system produces large amounts of dilute
urine.
Terrestrial animals use a variety
of methods to reduce water loss: living
in
moist
environments,
developing
impermeable body coverings, production
of more concentrated urine. Water loss
can be considerable: a person in a 100
degree F temperature loses 1 liter of
water per hour.
Excretory System Functions
1. Collect
water
and
filter
body
fluids.
2. Remove
and
concentrate
waste
products
from
body
fluids
and
return other substances to body
fluids
as
necessary
for
homeostasis.
3. Eliminate excretory products from
the body.
Notes in Animal Physiology by CCDivina…………
151
Invertebrate Excretory Organs
Many
invertebrates
such
as
flatworms use a nephridium as their
excretory organ. At the end of each
blind tubule of the nephridium is a
ciliated flame cell.
As fluid passes down
the tubule, solutes are reabsorbed and
returned to the body fluids.
Excretory
system
of
a
flatworm.
Excretory system of an earthworm.
Image from Purves et al., Life: The Science of
Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com)
and
WH
Freeman
(www.whfreeman.com),
Body fluids are drawn into the
Malphigian tubules by osmosis due to
large concentrations of potassium inside
the tubule. Body fluids pass back into
the body, nitrogenous wastes empty into
the insect's gut. Water is reabsorbed
and waste is expelled from the insect.
Notes in Animal Physiology by CCDivina…………
152
Excretory system of an ant. Images from Purves et
al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates (www.sinauer.com) and WH
Freeman (www.whfreeman.com),
Vertebrates Have Paired Kidneys
ALL
vertebrates
have
paired
kidneys. Excretion is not the primary
function of kidneys. Kidneys regulate
body fluid levels as a primary duty, and
remove wastes as a secondary one.
The Human Excretory System
The urinary system is made-up of
the
kidneys,
ureters,
bladder,
and
urethra. The nephron, an evolutionary
modification of the nephridium, is the
kidney's
functional
unit.
Waste
is
filtered from the blood and collected as
urine in each kidney. Urine leaves the
kidneys by ureters, and collects in the
bladder. The bladder can distend to
store
urine
that
eventually
leaves
through the urethra.
Notes in Animal Physiology by CCDivina…………
153
Notes in Animal Physiology by CCDivina…………
154
The Nephron
The nephron consists of a cupshaped capsule containing capillaries
and the glomerulus, and a long renal
tube.
Blood
flows
into
the
kidney
through the renal artery, which branches
into capillaries associated with the
glomerulus.
Arterial
pressure
causes
water and solutes from the blood to
filter into the capsule. Fluid flows
through
the
proximal
tubule,
which
include the loop of Henle, and then into
the distal tubule. The distal tubule
empties into a collecting duct. Fluids
and
solutes
are
returned
to
the
capillaries that surround the nephron
tubule.
The nephron has three functions:
1. Glomerular filtration of water and
solutes from the blood.
2. Tubular reabsorption of water and
conserved molecules back into the
blood.
3. Tubular secretion of ions and other
waste
products
from
surrounding
capillaries into the distal tubule.
Nephrons filter 125 ml of body fluid
per minute; filtering the entire body
fluid component 16 times each day. In a
24 hour period nephrons produce 180
liters of filtrate, of which 178.5
liters are reabsorbed. The remaining 1.5
liters forms urine.
Notes in Animal Physiology by CCDivina…………
144
Urine Production
1. Filtration in the glomerulus and
nephron capsule.
2. Reabsorption
in
the
proximal
tubule.
3. Tubular secretion in the Loop of
Henle.
Components of The Nephron





Glomerulus:
mechanically
filters
blood
Bowman's
Capsule:
mechanically
filters blood
Proximal
Convoluted
Tubule:
Reabsorbs 75% of the water, salts,
glucose, and amino acids
Loop
of
Henle:
Countercurrent
exchange,
which
maintains
the
concentration gradient
Distal Convoluted Tubule: Tubular
secretion of H ions, potassium, and
certain drugs.
Kidney Stones
In
some
cases,
excess
wastes
crystallize as kidney stones. They grow
and can become a painful irritant that
may
require
surgery
or
ultrasound
treatments. Some stones are small enough
to be forced into the urethra, others
are the size of huge, massive boulders
(or so I am told).
Kidney Function
Notes in Animal Physiology by CCDivina…………
145
Kidneys perform a number of homeostatic
functions:
1. Maintain volume of extracellular
fluid
2. Maintain
ionic
balance
in
extracellular fluid
3. Maintain
pH
and
osmotic
concentration of the extracellular
fluid.
4. Excrete toxic metabolic by-products
such as urea, ammonia, and uric
acid.
Hormone Control of Water and Salt
Water reabsorption is controlled by
the
antidiuretic
hormone
(ADH)
in
negative feedback. ADH is released from
the
pituitary
gland
in
the
brain.
Dropping levels of fluid in the blood
signal the hypothalamus to cause the
pituitary to release ADH into the blood.
ADH acts to increase water absorption in
the kidneys. This puts more water back
in
the
blood,
increasing
the
concentration of the urine. When too
much fluid is present in the blood,
sensors
in
the
heart
signal
the
hypothalamus to cause a reduction of the
amounts of ADH in the blood. This
increases the amount of water absorbed
by
the
kidneys,
producing
large
quantities of a more dilute urine.
Aldosterone, a hormone secreted by
the kidneys, regulates the transfer of
sodium from the nephron to the blood.
Notes in Animal Physiology by CCDivina…………
146
When sodium levels in the blood fall,
aldosterone is released into the blood,
causing more sodium to pass from the
nephron to the blood. This causes water
to flow into the blood by osmosis. Renin
is released into the blood to control
aldosterone.
Disruption of Kidney Function
Infection,
environmental
toxins
such as mercury, and genetic disease can
have devastating results by causing
disruption of kidney function. Many
kidney
problems
can
be
treated
by
dialysis, where a machine acts as a
kidney.
Kidney
transplants
are
an
alternative to dialysis.
Gout is a disorder in which humans
start to accumulate more than the usual
amount of uric acid (caused by either
the body manufacturing excess uric acid
or the kidneys not excreting enough of
it) and since it’s not water-soluble, it
gets stored in the body, frequently in
toe joints, causing pain and deformation
of the joints involved as well as the
formation
of
kidney
stones.
Traditionally, people who had gout were
put on diets low in purines to try to
help alleviate the condition. Typically,
gout is treated with colchicine, a
deadly
poison
Caffeine
and
its
relatives, theobromine (in cocoa), and
theophylline (in tea) are classified as
xanthines
(a
subgroup
within
the
purines), thus it would make sense that
Notes in Animal Physiology by CCDivina…………
147
people with gout should be counseled to
avoid coffee, tea, and chocolate.
Some
insects,
notably
blowfly
larvae (larvae of those shiny green or
blue flies) excrete their nitrogenous
wastes as allantoin, another purine.
Allantoin is known to be a “cellproliferant,” thus is used to help
wounds to heal. For hundreds of years,
people have recognized that the presence
of blowfly larvae in a gangrenous wound
actually helped it to heal better. From
about the turn of the century until the
invention of a lot of synthetic drugs,
blowfly larvae were raised aseptically,
and used to treat severe wounds. With
the
increase
in
availability
of
chemicals after World War II, the use of
blowfly larvae declined,
for some
reason, this treatment was necessary
and/or preferred over synthetic drugs.
It has been found that the fly larvae
only
eat
dead,
gangrenous
tissue,
leaving the live, healthy tissue, and
since
their
nitrogenous
waste
is
allantoin, that stimulates the wound to
heal, usually with less scaring. In this
procedure, small, sterile larvae are
introduced
into
the
wound
and,
if
needed, traded for other small ones when
they get big.
We excrete nitrogenous wastes via
our kidneys. Our kidneys are located on
either side of the spine, just up under
the bottom ribs. They are well supplied
with blood via the renal artery and
Notes in Animal Physiology by CCDivina…………
148
renal vein. Urine made in the kidney
collects in the renal pelvis within the
kidney, then flows down the ureter to
the bladder where it is stored until
voided. From the bladder, the urine
flows to the outside via the urethra,
(which in the male also serves as part
of the reproductory tract).
The kidney is composed of an outer
layer, the cortex, and an inner core,
the medulla. The kidney consists of
repeating
units
(tubules)
called
nephrons. The “tops” of the nephrons
make up or are in the cortex, while
their long tubule portions make up the
medulla. To the right is a diagram of an
individual nephron. Each nephron has a
closely associated blood supply. Blood
comes in at the glomerulus and transfers
water and solutes to the nephron at
Bowman’s
capsule.
In
the
proximal
tubule, water and some “good” molecules
are absorbed back into the body, while a
few other, unwanted molecules/ions are
added to the urine. Then, the filtrate
goes down the loop of Henle (in the
medulla) where more water is removed
(back into the bloodstream) on the way
“down”, but the “up” side is impervious
to water. Some NaCl (salt) is removed
from the filtrate at this point to
adjust the amount in the fluid which
surrounds the tubule. Capillaries wind
around and exchange materials with the
tubule. In the distal tubule, more water
and some “good” solutes are removed from
the urine, while some more unwanted
Notes in Animal Physiology by CCDivina…………
149
molecules are put in. From there, the
urine flows down a collecting duct which
gathers urine from several nephrons. As
the collecting duct goes back through
the medulla, more water is removed from
the
urine.
The
collecting
ducts
eventually end up at the renal pelvis
which collects the urine from all of
them. The area where the collecting
ducts enter the renal pelvis is a common
area for formation of kidney stones,
often giving them a “staghorn” shape.
Antidiuretic hormone (ADH) from the
pituitary is one factor influencing
urine production. ADH promotes water
retention
by
the
kidneys,
and
its
secretion is regulated by a negative
feedback loop involving blood water and
salt balances. ADH helps the kidney
tubules reabsorb water to concentrate
the urine. When the blood water level is
too high (when you’ve been drinking a
lot of liquids), this acts as a negative
feedback to inhibit the secretion of ADH
so more water is released. Ethanol also
inhibits secretion of ADH, so a person
who
consumes
a
lot
of
alcoholic
beverages could excrete too much water
(and maybe even become dehydrated). Many
diuretics work by interfering with ADH
production, thus increasing the volume
of
urine
produced.
These
diuretic
effects are one reason why a person
drinking
beer
(alcohol)
or
coffee
(caffeine)
needs
to
urinate
more
frequently.
Notes in Animal Physiology by CCDivina…………
150
When
a
person’s
kidneys
cease
functioning, due to illness or other
causes, renal dialysis can be used on a
short-term basis to filter the person’s
blood. This is not a perfect process; it
can’t do everything a person’s kidneys
can. Typically a person is put on renal
dialysis as a temporary measure to
extend the person’s life until a kidney
transplant can be found. While lifesaving, this procedure is often very
inconvenient
and
stressful
for
the
person.
It
requires
spending
long
periods of time, several days a week,
hooked up to the dialysis machine: the
person’s blood must actually pass into
the dialysis machine so the wastes can
be filtered out, and then the blood is
returned to the person’s body. This,
combined with symptoms caused by the
renal failure (the inability of the
person’s kidneys to function) often
preclude working at a job to earn the
money to pay for the treatment. People
can get by with one kidney, and the
closest
tissue
match
for
a
kidney
transplant is often a sibling.
Some diseases and disorders
excretory system include:

of
the
Nephritis is an inflammation of the
glomeruli, due to a number of
possible causes, including things
like strep throat. Symptoms include
bloody urine, scant urine output,
and
edema
(swelling/puffliness).
Another, more severe form, is due
Notes in Animal Physiology by CCDivina…………
151
to an autoimmune attack on the
glomeruli. Other types of nephritis
affect the tubules.


Nephrosis
also
affects
the
glomeruli, and is characterized by
excretion
of
abnormally
large
amounts of protein (often causing
“foamy”
urine)
and
generalized
edema
(water
retension/swelling)
throughout
the
whole
body,
especially
noted
as
“puffy”
eyelids.
Because
these
people’s
kidneys often do not handle sodium
properly,
a
low-salt
diet
is
usually
prescribed.
My
younger
brother developed nephrosis at age
4, and to control it, had to stay
on a no-added-salt diet and take
prednisone on a regular basis from
then until age 16, at which point,
his
body
finally
responded
positively to being weaned off the
drug.
Most
urinary
tract
infections
(UTIs) are caused by Gram negative
bacteria such as E. coli. If there
is an obstruction of the urethra,
catheterization may be needed, but
as a general rule, catheterization
in cases of UTI is contraindicated
because it can actually introduce
pathogens and make the infection
Notes in Animal Physiology by CCDivina…………
152
worse. Women tend to acquire more
urethral
and
bladder
infections
than
men,
perhaps
because
the
opening of the urethra is closer to
the anus. The way a woman cleans
the area after relieving herself
can
influence
her
chances
of
contracting a UTI and/or vaginal
infection. When parents are toilettraining
toddlers,
the
common
mistake is to wipe young girls from
back to front. The toddlers get
used to this feeling, and when they
start to wipe themselves, they also
go
from
back
to
front.
This
technique wipes bacteria from the
anal area towards or into the ends
of the vagina and urethra. Rather,
young girls should be trained to
wipe from front to back, and women
who were not trained this way
should make a conscious effort to
change their habits.

There are a variety of types of
kidney stones depending on what
conditions caused their formation.
According to the Merck Manual,
these are calcium oxalate (and/or
other calcium-based stones), uric
acid, cystine, and the other due to
magnesium
ammonium
phosphate
or
other
causes.
Stones
may
be
microscopic
to
large
“staghorn”
stones that fill the whole renal
pelvis. Often, as the stone is
Notes in Animal Physiology by CCDivina…………
153
passed down the ureter, the person
experiences much pain, and the
affected
kidney
may
even
temporarily become nonfunctional.
Stones
may
be
broken
up
by
ultrasound so they can be passed
more easily, but large stones may
have to be surgically removed. If
possible, the underlying cause of
the stone(s) should be identified
and
alleviated.
For
example,
calcium stones might be caused by
anything from a parathyroid gland
problem to too much vitamin D to
some forms of cancer to a genetic
predisposition.
Nervous System
Nervous system performs the three
overlapping functions of sensory input,
integration and motor output. Its three
main
functions
are
sensory
input
,integration
and
motor
output
to
effectors cells.
The
central
nervous
(CNS)
integrates
information,
while
the
interconnecting nerves of the peripheral
nervous
system
(PNS)
communicate
sensory and motor signals between the
CNS and the rest of the body.
Notes in Animal Physiology by CCDivina…………
154
The nervous system is composed of
neurons and supporting cells. The CNS
(Central Nervous System) consists of the
brains and spinal cord.
Central Nervous system
Neurons
contain
the
molecular
machinery common to all cells. When not
too
severely
damaged,
neurons
in
peripheral nerves can regrow. Nerve
cells are so specialized, however, that
they can no longer reproduce by cell
division.
And
even
regrowth
is
impossible
in
the
central
nervous
system. This is why severe damage to the
brain or spinal cord is permanent and
can result in muscle or limb paralysis.
Messages to activate those structures
cannot be carried past the point of
injury.
The brain also has a class of cells
called glia. Glial cells are shaped to
fit into the spaces between neurons.
They
stabilize
the
brain's
neural
circuits
and
also
supplement
the
metabolic processes of neurons.
The nervous system--the brain, the
spinal
cord,
and
the
nerves--also
controls body activities. The lower
parts
of
the
brain
control
basic
functions such as breathing and heart
rate
as
well
as
body
temperature,
hunger, and thirst. Above these regions
are the centers for sight, sound, touch,
smell, and taste, and the regions that
Notes in Animal Physiology by CCDivina…………
155
direct voluntary muscular activities of
the arms and legs. Performed here are
the higher functions of integrating and
processing information.
The
brain
receives
and
sends
information by means of nerves, many of
which lie partly in the spinal cord. The
spinal cord is protected by the spinal
column. Nerves enter and leave the
spinal cord at each level of the body,
traveling to and from the arms, legs,
and
trunk.
These
nerves
bring
information
from
the
various
sense
organs. The information is processed by
the brain, and then messages are carried
back to muscles and glands throughout
the body.
The
Peripheral
Nervous
System
contains
sensory
neurons,
which
transmits information from the internal
and external environment of the CNS and
motor neurons, which carry information
form
the
CNS
to
target
organs,
intermediate
neurons
of
the
CNS
integrate sensory input and motor outs.
Impulses
are
action
potentials,
electrical
signals
propagated
along
neurons membranes
The membrane potential of a nontransmitting
neuron
is
due
to
the
unequal
distribution
of
ions,
particularly sodium and potassium across
the plasma membrane, the cytoplasm is
more
negatively
charged
than
the
Notes in Animal Physiology by CCDivina…………
156
extracellular fluid, membrane potential
is
maintained
by
differential
permeabilities and the sodium-potassium
pump.
A
stimulus
that
affects
the
membranes’ permeability
to ion can
either depolarize of hyperpolarize the
membrane relative the membrane’s resting
potential, this local voltage change is
called
a
graded
potential
opens
voltage-gated sodium channels and the
rapid influx of f Na bring the membrane
to potential to a positive value, the
membrane potential is restored to its
normal
sting
value
by
the
delayed
opening of voltage gate
K+
channels
and by the closing of the Na + channels
. a refractory period follows an action
potential, corresponding to the period
when the voltage-gated Na
channels are
inactivated.
The all or none generation of an
action potential always creates the
sample amplitude of voltage change for a
given neuron. The frequency of action
potential varies with the intensity of
the stimulus.
Once an action potential is initiated
in
axon,
a
wave
of
depolarization
propagates,
a
series
of
action
potentials to the end of the axon.
The rate of transmission of a nerve
impulse is directly related to the
diameter
of
the
axons.
Saltatory
Notes in Animal Physiology by CCDivina…………
157
conduction, a mechanism by which action
potential jump between the nodes of
ranvier of myelinated axons, speeds
nervous impulses in
Nerves, unlike telephone wires with
which they are compared, generate their
own self-amplified electrical signals-the nerve impulses. The electrical sign
of
a
nerve
impulse
is
an
action
potential (AP), and it is generated when
a neuron undergoes electrical change.
Electrically charged ions are in varying
concentrations inside and outside a
cell, causing a voltage difference on
each side of the cell membrane. In a
"resting" neuron the voltage difference
is called the resting potential. The
inside
of
a
neuron
at
rest
is
electrically more negative than the
outside, usually by between -50 and -100
millivolts (mV). In this condition the
nerve membrane is polarized.
When a voltage change brought on by
a stimulus depolarizes the membrane,
either of two things happens. If the
stimulus is strong enough to breach a
critical threshold level, an action
potential is fired. If not, the voltage
drops back to the resting potential.
An action potential moves along an
axon at speeds of up to ten yards per
second.
The
voltage
change
and
depolarization at one end of the axon
"flows" to the next point, where the
event is duplicated, and so on down the
Notes in Animal Physiology by CCDivina…………
158
axon until
terminals.
the
AP
reaches
the
axon
Scientists have a fairly clear idea
of how APs form in a neuron. When a
portion of the membrane is depolarized,
special channels in it open and allow an
inward rush of sodium ions, which are in
higher concentration outside the cell.
Then when the positively charged sodium
ions flow into the negatively charged
neuron interior, they cause further
depolarization by making the interior
electrically more positive. This, in
turn, opens more channels, allowing more
sodium ions to rush in. Once opened,
however, the sodium channels slowly
close in spite of the depolarization
that originally made them open. Channels
for outgoing potassium ions are also in
the neuron membrane. They, too, open
during depolarization but more slowly
than the sodium channels. When the
potassium
channels
finally
open,
positively charged potassium ions flow
to the outside of the cell, where they
are in lower concentration. As they
leave the cell, they hasten the return
of the neuron's voltage to its resting
level, and the interior again becomes
electrically more negative than the
exterior.
APs travel faster in some neurons than
in others. This is because some have
fatty myelin separating short segments
of bare axon that are called nodes of
Ranvier. In a myelinated axon the action
Notes in Animal Physiology by CCDivina…………
159
potential jumps from one node to the
next instead of traveling along the
entire length of the axon as it must in
an unmyelinated axon.
Chemical
or
electrical
communication
between cells occur at synapses
The membrane potential of a nontransmitting
neuron
is
due
to
the
unequal
distribution
of
ions,
particularly sodium and potassium across
the plasma membrane, the cytoplasm is
more
negatively
charged
than
the
extracellular fluid, membrane potential
is
maintained
by
differential
permeabilities and the sodium-potassium
pump.
A
stimulus
that
affects
the
membranes’ permeability
to ion can
either depolarize of hyperpolarize the
membrane relative the membrane’s resting
potential, this local voltage change is
called
a
graded
potential
opens
voltage-gated sodium channels and the
rapid influx of f Na bring the membrane
to potential to a positive value, the
membrane potential is restored to its
normal
sting
value
by
the
delayed
opening of voltage gate
K+
channels
and by the closing of the Na + channels
. a refractory period follows an action
potential, corresponding to the period
when the voltage-gated Na
channels are
inactivated.
Notes in Animal Physiology by CCDivina…………
160
The all or none generation of an
action potential always creates the
sample amplitude of voltage change for a
given neuron. The frequency of action
potential varies with the intensity of
the stimulus.
Once
an
action
potential
is
initiated
in
axon,
a
wave
of
depolarization propagates, a series of
action potentials to the end of the
axon.
The rate of transmission of a nerve
impulse is directly related to the
diameter
of
the
axons.
Saltatory
conduction, a mechanism by which action
potential jump between the nodes of
ranvier of myelinated axons, speeds
nervous impulses in
The human brain.
In the human brain, the midbrain
and hindbrain make up the brain stem.
The medulla oblongata and pons of the
hindbrain
work
together
to
control
homeostatic
functions
and
conduct
together
to
control
homeostatic
functions and conduct sensory and motor
signals between the spinal cord and
higher brain centers. The cerebellum of
the hindbrain coordinates movement and
balance.The
midbrain
receives,
integrates
and
protects
sensor
information of the forebrain.
Notes in Animal Physiology by CCDivina…………
161
The forebrain is the site of the
most sophisticated neurons processing
with major integrating centers in the
thalamus, hypothalamus and cerebrum. The
thalamus routes neural input to specific
areas of the cerebral cortex the outer
gray matte of the cerebrum. The function
of the hypothalamus range form hormone
production to the regulation of body
temperature hunger , thirst, sexual
response, the fight o fight response and
biorhythms
The
cerebral
cortex
contains
distinct
somatosensory
motor
areas,
which directly process information and
association
areas,
which
integrate
information. Imaging technology enables
researchers
to
identify
specific
integrating centers in the functioning
brain.
Several areas in the cerebrum and
brain stem the most important being the
reticular formation, which filters the
sensory
input
sent
to
the
cortex,
control sleep and arousal.
The
two
cerebral
hemispheres
control
different
function,
Speech,
language and analytical ability are
centers in the left hemispheres whereas
spatial perception and artistic ability
predominate in the right. Nerve
tracts
of the corpus collosum link the two side
and allow the brain to function as an
integrated whole.
Notes in Animal Physiology by CCDivina…………
162
Human emotions are believed to
originate from interactions between the
limbic system , a group of nuclei in the
diencephalons and inner cerebrum, the
limbic system interacts closely with the
prefrontal cortex, a higher integrative
control of the forebrain.
Human memory consists of short term
and long-term memories. the process of
learning fact appears to differ from
that of learning skills. The hippocampus
and amygdala. Two components of the
limbic
system
participate
in
the
circular
pathways
involved
in
fact
memory.
A functional change at synapses,
called long-term potentiation (LTP) may
underlay memory stage and learning.
Resulting from repeated burst of action
potential
or
LPG
is
heightened
sensitivity to a single action potential
by a postsynaptic membrane.
Mammalian Nervous System
NEURAL evolution has reached its
present peak within the Class Mammaliabut
read
that
"within"
with
understanding. Most mammals in fact have
a brain that is little more developed in
a mental sense than that of birds. Here
it is very easy to slip into teleology
and anthropomorphic chauvanism. Wow.
Anyway, in your enthusiasm with having a
mind, keep in your mind that evolution
is fully at work and the most stupid
Notes in Animal Physiology by CCDivina…………
163
duckbill knows more about how to be a
duckbill than you ever could.
The mammalian brain has made major
advancements within two regions. The
cerebellum
has
expanded
greatly
in
volume, but more importantly, it has
become much folded in all species. The
cerebellar cortex is vastly increased in
surface area by this folding into many
folia. Cortical cells interrelate in an
inclosed grouping (called a "column" or
"barrel") that is perpendicular to the
cortical
surface.
The
greater
the
surface area (not volume), the more
numerous these columns can be...and,
thus,
the
greater
the
processing
capacity. The human cerebellum is about
the size of a human fist, yet if the
folding were flattened, the cerebellum
would be about 45 cm wide and 25 m long
to yield a rather strangely shaped
cranium.
The cerebellum has only a vague
local sign...that is, association with a
particular body region. Further, it is
always active, whether the muscular
system is busy or not. An understanding
of its general function was gained early
on, because this is the only brain
region which can be removed surgically
and have the subject survive and thrive
(but not unchanged). In fact, although
the cerebellum itself is not involved
with
Parkinsonism,
it
does
receive
faulty input from higher motor centers
that result in characteristic tremors.
Notes in Animal Physiology by CCDivina…………
164
An
early
surgical
remedy
involved
cerebellumectomy, which did nothing for
the course of the disease but did
relieve palsy symptoms.
Cerebellar
function
in
lower
vertebrates
centers
around
muscular
coordination with sense of balance to
maintain body position. At some point in
subsequent
evolution
of
this
brain
division, it began to take on other
functions. All proprioceptive (muscle
and joint sense) input to the brain is
referred (only) to the cerebellum in
mammals. In addition all locomotor and
postural motor decisions are referred to
cerebellar cortex before implementation.
The cerebellum then compares the present
position of the body relative to the
center of the earth, the angle subtended
by all joints, and the current effort
being put out by the muscular system-all
of these factors are compared with the
instructions about to be issued by
cerebral motor centers. The cerebellum
then "advises" the cerebrum how best to
achieve its goal, considering what the
body is presently doing.
Many cerebral functions have
exact local sign, such as sense of
touch, precise motor control, and
the special senses of vision and
hearing (pitch). The sides and
apices of gyri have larger number
of neurons and of synapses, and the
cortex itself is thicker, compared
to the floor of a sulcus. Thus, it
Notes in Animal Physiology by CCDivina…………
165
is not surprising that such primary
areas often have precise functional
boundaries that correspond to the
floors of sulci. A gyrus may not
only
be
specifically
identified
with a particular operation, but
there may be linear correlations
along the length of that gyrus with
particular aspects. For example,
both of the temporal lobe gyri in
humans that are responsible for
appreciation of sense of touch and
for very precise motor control can
be mapped from ventral to dorsal in
a distorted but recognizable figure
of the body. These distortions
represent variation in sensitivity
or precision. For instance, the
areas devoted to fingers (sensory
and motor) are larger than gyral
area representing the entire body
trunk.
The three meninges of the CNSrespectively pia mater, arachnoid,
and outermost dura mater-was well
differentiated in mammals. Unlike
most vertebrate forms, the brain
lies close against the inner layer
of the skull. This relationship is
displayed
in
many
gyrencephalic
mammals as negative ridges and
grooves representing the folding
patterns
of
the
cerebral
and
cerebellar cortices. This creates a
kind of fossil brain image, and
endocasts
of
extinct
species
permits study of brain evolution in
Notes in Animal Physiology by CCDivina…………
166
ancient forms. This patterning does
not develop in human crania except
for the imprint of surface blood
vessels.
FREQUENTLY ASKED QUESTIONS
What is the difference between a neuron
and a glial cell?
Neurons and glial cells are the
basic
components
of
neural
control
system. The neurons or nerve cell is the
fundamental
information-processing
units,
receiving
and
integrating
information from external and internal
environment, and using this information
to
control
effectors
(muscles
and
glands. The neuron has two specialized
properties for this task: irritability
or
excitatory
and
conductivity.
Irritability – a property fond to some
degree in all cells – is the capacity to
respond to environmental stimuli for a
neuron, these stimuli are conducted
messages in the form of electrochemical
impulses coming to it from sensory
receptors and other neurons, the neuron
responds to theses stimuli by passing o
its own flow of coded electrochemical
impulses. The term conductivity, when
used with a wire in an electric circuit,
referred to wire’s ability to carry or
conduct an electric current with a
neuron, conductivity is the ability to
conduct a current of electrochemical
impulses along its own length an the to
Notes in Animal Physiology by CCDivina…………
167
transmit
to
effectors.
the
next
neuron
or
The other basic component of the
neural control system, the glial (or
neuroglial) cells as their name implies,
“glue” the neural systems together.
Because
glial
cells
surround
the
neurons, they are able to insulate
neurons form the rest of the body and
provide them with many life-support
services
glial cells bring neurons the
substances for the rest of the body and
provide them with many life-support
services. Glial cells bring neurons the
substances
for
metabolism,
remove
metabolism
wastes
and
debris
from
damaged or dead neurons, and regulate
the chemistry of the fluid bathing the
neurons. Insulate the neurons form each
other to prevent interference between
the electrochemical message channels and
provide myelin sheaths for salutatory
conduction. There are many types of
glial cells, astrocytes, which form the
brood-brain barrier by lining brains
capillaries.
Oligodendroglial
cells,
which are the glial support cells for
the vertebrate central nervous system (
brain and spinal cord and
Schwann
cells, which perform the latter function
in the vertebrate peripheral nervous
system, .
Three major trends that affected the
evolution
of
nervous
systems
are
centralization, the change from radial o
Notes in Animal Physiology by CCDivina…………
168
bilateral symmetry and cephalization.
What are these trends and how did they
affect this evolution.
Because the neural tissues are
rarely preserved in fossils, scientist
have had to piece together the early
evolution of nervous systems for stages
seen n living representative of early
animal. Of these, it now seem that
modern cnidarians,
( sea anemones.
Hydra, jellyfish) are most similar to
the fires animals to have neurons and
nervous systems/.
The modern cnidarians are radially
symmetrical: there is no front and back
or right and left sides, instead the
body parts are organized circularly,
like spokes radiating
from the center
of
a
wheel.
The
cnidarians
have
identical
neurons
interconnected
by
synapses crisscross the body. The net
transmits
information
from
sensory
receptors cell to muscle like effectors
cell. When the sensory cell react to
chemical
or mechanical stimuli, the
receptor glial cell to like effectors
cells. When the sensory cells react to
chemical or mechanical stimuli, the
neuron message radiates outward along
the net in all direction’s producing
contractions
in
large
number
of
effectors cells. This allows some degree
of coordination of localized responses,
such as the movement of a tentacle .
Notes in Animal Physiology by CCDivina…………
169
Also seen in a modern cnidarians,
the
jellyfish
,
is
somewhat
more
advanced nervous system that showed the
first evidence of centralization: the
gathering together of neuron to form
control center’s in he jellyfish, this
takes the form a ring of neurons around
its bell-shaped body, the ring produces
coordinated
whole-body
swimming
movements.
A
major
advancement
in
the
evolution of nervous systems accompanied
the
appearance
of
animals
with
bilaterally symmetrical bodies, which
are organized on a longitudinal axis
with right and left sides that are
mirror images of each other. This type
of body has a distinct anterior end and
posterior
end,
dorsal
surface
and
ventral surface.
The first simplest animals
to
exhibit this type of organization were
the flatworms, represented today by such
forms as the planarian, these animals
show an increasing centralization, with
neurons
gathered
together
to
form
pathways and control center. Bundles
containing the somas and fibers of
neurons form two parallel nerve controls
that extent the full length of the body.
In the animal end, or head , the nerve
cord
fuse
to
form
ganglion
(
a
collection of somas and synapses.)_ this
accumulation of neural tissue in the
head end is thought to represent
the
first example of evolutionary terms
called
cephalization.
Although
this
Notes in Animal Physiology by CCDivina…………
170
planarian cephalic (situated in the head
ganglion is quit primitive, it has been
called the first brain)
Increasing
centralization
and
cephalization occurred in the evolution
of the bilateral nervous system, in both
the invertebrates (annelids, mollusks,
cephalopods, arthropods and vertebrates.
In many advanced invertebrate, there is
a central nervous system consisting of
paired , solid ventral nerve cords with
glia in each segment of the body, and a
dominant ganglion,(brain) in the head,
In vertebrates, the central nervous
system is a single, hollow, dorsal nerve
cord
(the
spinal
cord
with
no
conspicuous segmental ganglia and with a
large doming brain in the head.
You are watching a horror movie and
you notice that your heart is beating
fast, your mouth is dry and you a
breathing rapidly.

You are experiencing some f the
more noticeable components of the fightor
fight
response
produce
by
the
sympathetic division of the autonomic
nervous
system.
In
general,
the
sympathetic systems prepares and animal
to respond to an emergency, to be able
to fight it or flee from it, which the
other
autonomic
divisions,
the
parasympathetic system, works to restore
than conserve energy. It is seen there
that most but not all , body organs are
Notes in Animal Physiology by CCDivina…………
171
innate by both systems, and often they
have opposite (antagonistic
effects on
the same organs. One major difference
between
the
systems
are
while
the
parasympathetic
exits
the
central
nervous system in the cranial and sacral
nerves, the sympathetic exits through
thoracic
and
lumbar
nerve,
whole
preganglionic
sympathetic
neurons
synapse with post ganglion fibers in a
chain of sympathetic ganglia enter and
on both sides of the spinal cord an the
parasympathetic
system, the synapse
between preganglions and postganglionic
takes place near the innervated ova.
 How
does environments information
reach the central nervous system?
An animals’ response to a change
into its external internal environments
coordinated
by
its
central
nervous
system, environmental information must
therefore
be
converted
into
neural
master before a response se can take
place. An environment change usually
involves some form of energy.
The
conversion of the environmental energy
into
the
electrochemical
energy
of
nerves is called transduction and is
performed by sensory cells.
Transduction and the transmission
of traduced information along afferent
neural pathways may be performed by a
single sensory cell or by a group of
sensory cells organized into a sensory
organ.
When a single sensory
cell
both traduces and transmits information,
Notes in Animal Physiology by CCDivina…………
172
it is called sensory neurons. The cell
membrane enclosing
dendrites of the
neuron responds to a particular form of
environmental energy by altering its
permeability to ions, which cause a
change in the membrane potential. the
new
potential
is
the
generator
potential of the sensory neurons and if
large enough, initiates at n action
potential in the icon that revels to the
central nervous site, Generate potential
vary greatly on value, they can be
larger or smaller than action potential,
which always have the same vale.
When
sensory
perform
both
transduction
and
transmission,
some
of
the cells are involved
in
transduction,
some
are accessory structures
and others are sensory
neuron ah transits the
information
to
the
Central nervous system,
Accessory structure focus, amplify or
localize the environmental energy before
it transducers. The lens of a vertebrate
eye. For example bends the light so that
it converges into the retina. The energy
is then transude by receptors cells when
the permeability of their membrane I as
so altered that ionic flow changes them
membrane
potential.
The
altered
potential; in a receptor cell is called
a
receptor
potential.
Like
the
generator
potential,
the
receptor
potential may be smaller of larger than
Notes in Animal Physiology by CCDivina…………
173
an action potential, if large enough ,
the
receptor
potential
alters
the
membrane potential in
the sensory
neurons to which it is connected by a
synapse. This change may initiate an
action potential in the axon of the
sensory neuron, the nerve impulse
is
then conveyed along eh afferent pathway
the central nervous system.
Its sensory cells accomplish all
detection
by
an
animal
of
the
environmental external to the animal’s
nervous system. Each type of sensory
cell is sensitive to a certain form of
energy, such as heat, light or sounds.
An animal can receive information only
if it has sensory cells that are capable
of
transuding
the
form
of
energy
accompanying the environmental event. An
animals’
sensory
cells
result
from
natural
selection
and
vary
for
different
species.
A
humans
lack
suitable sensory cells form any forms of
energy, including x-ray , radar and
radio or television waves, we detect
such
phenomena only after they have
been converted by mechanical devise into
forms of energy that our sensory cells
can
recognize, many animals can detect
environmental phenomenon that we cannot.
Bees see ultraviolet radiation, bats and
porpoises hear very high-pitched sounds,
snakes lock prey by sensing the heat
emanating from their prey’s bodies and
some fishes detect prey and mate by
means
of
electrical
currents.
Most
animals have sensory cells that respond
Notes in Animal Physiology by CCDivina…………
174
to mechanical, chemical thermal pain and
electromagnetic stimuli.
THE ENDOCRINE SYSTEM
The
nervous
system
coordinates
rapid and precise responses to stimuli
using action potentials. The endocrine
system maintains homeostasis and longterm control using chemical signals. The
endocrine system works in parallel with
the nervous system to control growth and
maturation along with homeostasis.
Hormones
The
endocrine
system
is
a
collection
of
glands
that
secrete
chemical messages we call
hormones.
These signals are passed through the
blood to arrive at a target organ, which
has cells possessing the appropriate
receptor. Exocrine glands (not part of
the endocrine system) secrete products
that are passed outside the body. Sweat
glands, salivary glands, and digestive
glands are examples of exocrine glands.
Notes in Animal Physiology by CCDivina…………
175
The roles of hormones in selecting
target cells and delivering the hormonal
message. Images from Purves et al.,
Life:
The
Science
of
Biology,
4th
Edition,
by
Sinauer
Associates
(www.sinauer.com)
and
WH
Freeman
(www.whfreeman.com).
Notes in Animal Physiology by CCDivina…………
176
Hormones
are
grouped
into
three
classes
based
on
their
structure:
steroids, peptides and amines
Steroids
Steroids are lipids derived from
cholesterol. Testosterone is the male
sex
hormone.
Estradiol,
similar
in
structure
to
testosterone,
is
responsible
for
many
female
sex
characteristics. Steroid hormones are
secreted by the gonads, adrenal cortex,
and placenta.
Notes in Animal Physiology by CCDivina…………
177
Structure of some steroid hormones and their
pathways of formation. Images from Purves et al.,
Life: The Science of Biology, 4th Edition, by
Sinauer
Associates
(www.sinauer.com)
and
WH
Freeman (www.whfreeman.com).
Peptides and Amines
Peptides are short chains of amino
acids; most hormones are peptides. They
are
secreted
by
the
pituitary,
parathyroid, heart, stomach, liver, and
kidneys. Amines are derived from the
amino acid tyrosine and are secreted
from
the
thyroid
and
the
adrenal
medulla.
Solubility
of
the
various
hormone classes varies.
Synthesis, Storage, and Secretion
Steroid hormones are derived from
cholesterol by a biochemical reaction
series. Defects along this series often
lead to hormonal imbalances with serious
consequences. Once synthesized, steroid
hormones pass into the bloodstream; they
are not stored by cells, and the rate of
synthesis controls them.
Peptide hormones are synthesized as
precursor molecules and processed by the
endoplasmic reticulum and Golgi where
they are stored in secretory granules.
When needed, the granules are dumped
into the bloodstream. Different hormones
can
often
be
made
from
the
same
precursor molecule by cleaving it with a
different enzyme.
Amine
hormones
(notably
epinephrine) are stored as granules in
the cytoplasm until needed.
Notes in Animal Physiology by CCDivina…………
178
Evolution of Endocrine Systems
Most animals with well-developed
nervous and circulatory systems have an
endocrine
system.
Most
of
the
similarities among the endocrine systems
of
crustaceans,
arthropods,
and
vertebrates are examples of convergent
evolution.
The
vertebrate
endocrine
system consists of glands (pituitary,
thyroid, adrenal), and diffuse cell
groups scattered in epithelial tissues.
More than fifty different hormones
are secreted. Endocrine glands arise
during
development
for
all
three
embryologic
tissue
layers
(endoderm,
mesoderm,
ectoderm).
The
type
of
endocrine product is determined by which
tissue layer a gland originated in.
Glands of ectodermal and endodermal
origin
produce
peptide
and
amine
hormones;
mesodermal-origin
glands
secrete hormones based on lipids.
Endocrine Systems and Feedback Cycles
The endocrine system uses cycles
and
negative
feedback
to
regulate
physiological
functions.
Negative
feedback regulates the secretion of
almost
every
hormone.
Cycles
of
secretion
maintain
physiological
and
homeostatic control. These cycles can
range from hours to months in duration.
Notes in Animal Physiology by CCDivina…………
179
Negative feedback in the thyroxine release
reflex. Image from Purves et al., Life: The
Science of Biology, 4th Edition, by Sinauer
Associates
(www.sinauer.com)
and
WH
Freeman
(www.whfreeman.com
Mechanisms of Hormone Action
The
endocrine
system
acts
by
releasing hormones that in turn trigger
actions
in
specific
target
cells.
Receptors on target cell membranes bind
only to one type of hormone. More than
fifty
human
hormones
have
been
identified;
all
act
by
binding
to
receptor molecules. The binding hormone
changes
the
shape
of
the
receptor
causing the response to the hormone.
There are two mechanisms of hormone
action on all target cells.
Nonsteroid Hormones
Nonsteroid hormones (water soluble)
do not enter the cell but bind to plasma
membrane
receptors,
generating
a
Notes in Animal Physiology by CCDivina…………
180
chemical
signal
(second
messenger)
inside the target cell. Five different
second messenger chemicals, including
cyclic AMP have been identified. Second
messengers activate other intracellular
chemicals to produce the target cell
response.
Notes in Animal Physiology by CCDivina…………
181
The action of nonsteroid hormones. Images from
Purves et al., Life: The Science of Biology, 4th
Edition, by Sinauer Associates (www.sinauer.com)
and WH Freeman (www.whfreeman.com),
Steroid Hormones
The
second
mechanism
involves
steroid hormones, which pass through the
plasma membrane and act in a two step
process. Steroid hormones bind, once
inside the cell, to the nuclear membrane
receptors,
producing
an
activated
hormone-receptor complex. The activated
hormone-receptor complex binds to DNA
and activates specific genes, increasing
production of proteins.
Notes in Animal Physiology by CCDivina…………
182
The action of steroid hormones. Images from
Purves et al., Life: The Science of Biology, 4th
Edition, by Sinauer Associates (www.sinauer.com)
and WH Freeman (www.whfreeman.com),
Endocrine-related Problems are due
to
overproduction
of
a
hormone
or
underproduction of a hormone or even
nonfunctional
receptors
that
cause
target cells to become insensitive to
hormones
The Nervous and Endocrine Systems
The pituitary gland (often called
the master gland) is located in a small
bony cavity at the base of the brain. A
stalk
links
the
pituitary
to
the
hypothalamus, which controls release of
pituitary hormones. The pituitary gland
has
two
lobes:
the
anterior
and
posterior lobes. The anterior pituitary
is glandular.
Notes in Animal Physiology by CCDivina…………
183
The endocrine system in females and males. Image
from Purves et al., Life: The Science of Biology,
4th
Edition,
by
Sinauer
Associates
(www.sinauer.com)
and
WH
Freeman
(www.whfreeman.com)
The hypothalamus contains neurons
that control releases from the anterior
pituitary.
Seven
hypothalamic
hormones
are
released
into
a
portal
system
connecting
the
hypothalamus
and
pituitary,
and
cause targets in
the pituitary to
release
eight
hormones.
Notes in Animal Physiology by CCDivina…………
184
The location and roles of the hypothalamus and
pituitary glands. Images from Purves et al.,
Life: The Science of Biology, 4th Edition, by
Notes in Animal Physiology by CCDivina…………
185
Sinauer
Associates
(www.sinauer.com)
Freeman (www.whfreeman.com),
and
WH
Growth hormone (GH) is a peptide
anterior pituitary hormone essential for
growth. GH-releasing hormone stimulates
release of GH. GH-inhibiting hormone
suppresses
the
release
of
GH.
The
hypothalamus
maintains
homeostatic
levels of GH. Cells under the action of
GH increase in size (hypertrophy) and
number (hyperplasia). GH also causes
increase in bone length and thickness by
deposition of cartilage at the ends of
bones. During adolescence, sex hormones
cause replacement of cartilage by bone,
halting further bone growth even though
GH is still present. Too little or two
much GH can cause dwarfism or gigantism,
respectively.
Hypothalamus
receptors
monitor
blood levels of thyroid hormones. Low
blood
levels
of
Thyroid-stimulating
hormone (TSH) cause the release of TSHreleasing hormone from the hypothalamus,
which in turn causes the release of TSH
from the anterior pituitary. TSH travels
to
the
thyroid
where
it
promotes
production of thyroid hormones, which in
turn regulate metabolic rates and body
temperatures.
Gonadotropins
and
prolactin
are
also secreted by the anterior pituitary.
Gonadotropins (which include folliclestimulating
hormone,
FSH,
and
luteinizing hormone, LH) affect the
gonads by stimulating gamete formation
Notes in Animal Physiology by CCDivina…………
186
and
production
of
sex
hormones.
Prolactin is secreted near the end of
pregnancy and prepares the breasts for
milk production.
The Posterior Pituitary
The
posterior
pituitary
stores
and
releases
hormones
into
the
blood.
Antidiuretic hormone (ADH) and oxytocin
are produced in the hypothalamus and
transported by axons to the posterior
pituitary where they are dumped into the
blood. ADH controls water balance in the
body and blood pressure. Oxytocin is a
small peptide hormone that stimulates
uterine contractions during childbirth.
Other Endocrine Organs
The Adrenal Glands
Each kidney has an adrenal gland
located above it. The adrenal gland is
divided into an inner medulla and an
outer cortex. The medulla synthesizes
amine hormones, the cortex secretes
steroid hormones. The adrenal medulla
consists
of
modified
neurons
that
secrete two hormones: epinephrine and
norepinephrine.
Stimulation
of
the
cortex by the sympathetic nervous system
causes release of hormones into the
blood to initiate the "fight or flight"
response. The adrenal cortex produces
several
steroid
hormones
in
three
classes:
mineralocorticoids,
glucocorticoids,
and
sex
hormones.
Mineralocorticoids maintain electrolyte
Notes in Animal Physiology by CCDivina…………
187
balance. Glucocorticoids produce a longterm, slow response to stress by raising
blood
glucose
levels
through
the
breakdown of fats and proteins; they
also suppress the immune response and
inhibit the inflammatory response.
The structure of the kidney as relates to
hormones. Image from Purves et al., Life:
The Science of Biology, 4th Edition, by
Sinauer Associates (www.sinauer.com) and WH
Freeman (www.whfreeman.com),
The Thyroid Gland
The thyroid gland is located in the
neck. Follicles in the thyroid secrete
thyroglobulin, a storage form of thyroid
hormone.
Thyroid
stimulating
hormone
(TSH) from the anterior pituitary causes
conversion of thyroglobulin into thyroid
hormones T4 and T3. Almost all body
cells are targets of thyroid hormones.
Thyroid
hormone
increases
the
overall metabolic rate, regulates growth
Notes in Animal Physiology by CCDivina…………
188
and development as well as the onset of
sexual maturity.
Calcitonin
is also
secreted by large cells in the thyroid;
it plays a role in regulation of
calcium.
The Pancreas
The
pancreas
contains
exocrine
cells that secrete digestive enzymes
into the small intestine and clusters of
endocrine cells (the pancreatic islets).
The islets secrete the hormones insulin
and
glucagon,
which
regulate
blood
glucose levels.
After a meal, blood glucose levels rise,
prompting the release of insulin, which
causes cells to take up glucose, and
liver and skeletal muscle cells to form
the carbohydrate glycogen. As glucose
levels
in
the
blood
fall,
further
insulin
production
is
inhibited.
Glucagon
causes
the
breakdown
of
glycogen into glucose, which in turn is
released into the blood to maintain
glucose levels within a homeostatic
range. Glucagon production is stimulated
when blood glucose levels fall, and
inhibited when they rise.
Diabetes results from inadequate levels
of
insulin.
Type
I
diabetes
is
characterized by inadequate levels of
insulin
secretion,
often
due
to
a
genetic cause. Type II usually develops
in
adults
from
both
genetic
and
environmental causes. Loss of response
of targets to insulin rather than lack
of insulin causes this type of diabetes.
Diabetes
causes
impairment
in
the
Notes in Animal Physiology by CCDivina…………
189
functioning of the eyes, circulatory
system, nervous system, and failure of
the kidneys. Diabetes is the second
leading cause of blindness in the US.
Treatments involve daily injections of
insulin, monitoring of blood glucose
levels and a controlled diet.
Other Chemical Messengers
Interferons are proteins released
when a cell has been attacked by a
virus. They cause neighboring cells to
produce
antiviral
proteins.
Once
activated, these proteins destroy the
virus.
Prostaglandins are fatty acids that
behave in many ways like hormones. They
are produced by most cells in the body
and act on neighboring cells.
Pheromones
are
chemical
signals
that travel between organisms rather
than between cells within an organism.
Pheromones are used to mark territory,
signal
prospective
mates,
and
communicate. The presence of a human sex
attractant/pheromone
has
not
been
established conclusively.
Biological Cycles
Biological
cycles
ranging
from
minutes to years occur throughout the
animal
kingdom.
Cycles
involve
hibernation,
mating
behavior,
body
Notes in Animal Physiology by CCDivina…………
190
temperature and many other physiological
processes.
Rhythms or cycles that show cyclic
changes on a daily (or even a few hours)
basis are known as circadian rhythms.
Many hormones, such as ACTH-cortisol,
TSH, and GH show circadian rhythms.
The menstrual cycle is controlled
by a number of hormones secreted in a
cyclical fashion. Thyroid secretion is
usually higher in winter than in summer.
Childbirth is hormonally controlled, and
is highest between 2 and 7 AM.
Internal
cycles
of
hormone
production
are
controlled
by
the
hypothalamus,
specifically
the
suprachiasmic nucleus (SCN). According
to one model, the SCN is signaled by
messages from the light-detecting retina
of the eyes.The SCN signals the pineal
gland in the brain to signal the
hypothalamus, etc.
From http://gened.emc.maricopa.edu/
Questions and Answers
Surgical removal of the posterior
pituitary
in
experimental
animals
results in marked symptoms, but these
symptoms
associated
with
hormone
shortage are temporary. Explain these
results.
Answer
Notes in Animal Physiology by CCDivina…………
191

The cell bodies of the neurosecretory
cells that produce ADH are in the
hypothalamus
and
their
axons
extend
into
the
posterior
pituitary, where ADH is stored
and
secreted.
Removing
the
posterior pituitary severs the
axons, resulting in a temporary
reduction
in
the
secretion.
However, the cell bodies still
produce
ADH.
And
as
ADH
accumulates
at
the
ends
of
severed
axons,
ADH
secretion
resumes.
Mr. Pablo has a son who wants to be
a basketball player almost as much as
Mr. Pablo wants him to be one. Mr.
Pablo knows a little about growth
hormone and asked his son’s doctor is
he would prescribe some for his son so
he can grow tall. What do you think
the doctor tells Mr. Pablo?

Answer:
If GH is administered to young people
before growth of their long bones is
complete, it will cause their long bone
to grow and they will grow taller.
However,
GH
would
have
to
be
administered over considerable length of
time. It is likely that some symptoms of
acromegaly would develop. In addition to
undesirable changes in the skeleton,
nerves frequently are compressed as a
result
of
the
proliferation
of
connective tissue. Because GH spares
Notes in Animal Physiology by CCDivina…………
192
glucose
usage
chronic
hyperglycemia
results frequently leading to diabetes
mellitus and the development of severe
atherosclerosis.
An
enlargement
of
the
thyroid
gland, called a goiter, develops when
there is too little iodine in the
diet. Explain why the thyroid gland
enlarges
in
response
to
iodine
deficiency in the diet?

Answer
The
thyroid
gland
enlarges
in
response
to
iodine
deficiency
because
without
iodine,
thyroid
hormones
cannot
be
synthesized.
Consequently, TSH levels in the
circulatory system increase because
of the lower than normal levels of
thyroid
hormone
in
the
blood.
Increased TSH levels cause the
thyroid gland to enlarge because it
continues
to
stimulate
thyroglobulin synthesis in large
amounts.
The
thyroid
follicles
enlarge; even the thyroid hormones
cannot be produced.
Predict the effect of an inadequate
dietary intake of calcium on PTH
secretion and on target tissues for
PTH.

Answer
In response to the reduced dietary
intake of calcium the blood levels of
calcium begin to decline. In response to
Notes in Animal Physiology by CCDivina…………
193
the decline in blood levels of calcium
there is an increase of PTH from the
parathyroid glands. The PTH functions to
increase calcium resorption from bone.
Consequently, blood levels of calcium
are maintained within the normal range
but at the same time bones are being
decalcified.
Severe
dietary
calcium
deficiency will result in bones that
become soft and eaten away because of
the decrease in calcium content.
A patient with a malignant tumor
has his thyroid gland removed, what
effect would this removal have on
blood levels of thyroid hormone, TRH,
TSH and calcitonin. What would result
if
the
parathyroid
glands
were
inadvertently removed during surgery?

Answer:
Removal of the thyroid gland would
remove
the
tissue
responsible
for
thyroid hormone production (follicles),
calcitonin (parafollicular cells) and
the PTH, (parathyroid are embedded in
the thyroid gland). Therefore, thyroid
hormones, calcitonins and PTH would no
longer be found in the blood. Without
the negative feedback effect of thyroid
hormones. TRH and TSH levels in the
blood would increase. Without, PTH blood
levels of calcium would fall. When blood
levels of calcium fall below normal, the
permeability of nerve and muscle cells
to solid increases. As a consequence,
spontaneous
action
potentials
are
produced that cause tetanus of muscles.
Notes in Animal Physiology by CCDivina…………
194
Death
can
result
respiratory muscle
from
tetany
of
Alterations in blood levels of
sodium and potassium have profound
effects in the electrical properties
of cells. Because high blood levels of
aldosterone cause retention of sodium
and excretion of potassium. Predict
and explain the effects of high
aldosterone levels on nerve and muscle
function.
Conversely,
because
low
blood levels of aldosterone cause low
blood levels of sodium and elevated
blood levels of potassium. Predict the
effects of low aldosterone levels on
nerve and muscle function.

Answer:
High aldosterone level in the blood
lead to elevated sodium levels in the
circulatory system and low blood levels
of potassium .the effect of low blood
levels
of
potassium
would
be
hyperpolarization of muscle and neurons.
The hyperpolarization results form a
greater tendency of potassium to diffuse
form the cell. As a result, a greater
than normal stimulus is required to
cause
the
cells
to
depolarize
to
threshold
and
generate
an
action
potential. Thus the symptoms include
lethargy
and
muscle
weakness.
The
elevated
sodium
concentration
would
result in a greater than normal amount
of water retention in the circulatory
Notes in Animal Physiology by CCDivina…………
195
system which can
blood pressure.
result
in
elevated
The major effect of a low rate of
aldosterone secretion is elevated blood
potassium levels. As a result nerve and
muscle cells depolarize, Because of
their
partial
depolarization
they
produce action potentials spontaneously
or in response to very small stimuli.
The result is a muscle spasms or tetany.
1. Cortisons,
a
drug
similar
to
cortisol, is sometimes given to
people who have severe allergies,
taking this substance chronically
can damage the adrenal cortex.
Explain how this damage can occur?
Answer
Large doses of cortisone can damage
the adrenal cortex because cortisone
inhibits
ACTH
secretion
from
the
anterior pituitary. ACTH is required to
keep adrenal cortex from undergoing
atrophy. Prolonged use of larges dose of
cortisone can cause the adrenal gland to
atrophy to the point at which it cannot
recover is CTH level do increase again.
Explain
they
the
increase
in
insulin
secretion
in
response
to
parasympathetic
stimulation
and
gastrointestinal
hormones
is
consistent with the maintenance of
blood
glucose
levels
in
the
circulatory system
Notes in Animal Physiology by CCDivina…………
196

Answer
An increase in insulin secretion in
response to parasympathetic stimulation
and
gastrointestinal
hormones
is
consistent
with
the
maintenance
of
homeostasis
because
parasymtpatic
t
stimulation increased gastrointestinal
hormones result from condition such as
eating a meal therefore, insulin levels
increase just before large amounts of
glucose
and
amino
acids
enter
the
circulatory system. The elevated insulin
levels prevents a large increase in
blood glucose and the loss of glucose in
the urine
Compare the regulation of glucagons
and insulin secretion after a meal
high in carbohydrate aw after a meal
low in carbohydrate but high in
proteins and during physical exercise.

Answer
In response to a meal high in
carbohydrates,
insulin
secretion
is
increased and glucagon secretion is
reduces. The stimulus for the insulin
secretion
comes
form
parasympathetic
stimulation and more important, from
elevated blood levels of glucose, in
response to a meal high in protein but
low in carbohydrates, insulin secretion
is increased slightly and glucagons
secretion
is
also
increased.
The
stimulation for insulin secretion is
parasympathetic stimulation and d an
increase in blood amino acid level.
Notes in Animal Physiology by CCDivina…………
197
Glucagon secretion is stimulated by low
blood glucose level and by some amino
acids.
During
periods
of
exercise,
sympathetic stimulation inhibits insulin
secretion.
As
blood
glucose
level
decline,
there
is
an
increase
of
glucagon secretion
Explain why long distance runners
may have much of a “kick” left when
they try to sprint to the finish line.

Answer:
Sympathetic
stimulation
during
exercise inhibits insulin secretion and
blood glucose level not high because of
the rapid metabolism of the small amount
of glucose that can enter the muscles.
Much
of
the
energy
for
muscle
contraction depends on glucose stored in
the form of glycogen in muscles and
during the end of the race results from
increased
energy
production
through
anaerobic
respiration,
which
uses
glucose or glycogen as an energy source.
Because
blood
glucose
levels
and
glycogen
levels
are
low,
there
is
insufficient
source
of
energy
for
greatly increased muscle activity.
Notes in Animal Physiology by CCDivina…………
198