Homeostasis
Glossary
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Maintain – keep up.
Constant – the same.
Internal – inside the body.
Environment – surroundings of the body.
What is Homeostasis?
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Body cells work best if they have the
correct
Temperature
 Water levels
 Waste levels
 Glucose concentration
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Your body has mechanisms to keep the
cells in a constant environment.
What is Homeostasis?
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The maintenance of a constant
environment in the body.
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The ability or tendency of an organism or
cell to maintain internal equilibrium by
adjusting its physiological processes.
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Physiology: is the study of the mechanical,
physical, and biochemical functions of living
organisms
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*Our bodies attempt to maintain an
internal balance called HOMEOSTASIS.
There are many conditions in which life
processes are limited:
Eg. Most enzymes in our bodies work
best at 37ºC.
pH of blood is maintained between 7.35
and 7.45. (recall – 7 is neutral, blood is
slightly basic)
Too low, acidosis
 Too high, alkalosis
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*MAJOR HOMEOSTATIC ORGAN
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Hypothalamus (brain) = Homeostasis
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The main function of the hypothalamus is
homeostasis, or maintaining the body's
status quo.
*MAJOR HOMEOSTATIC ORGAN
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The following factors are held to a precise
value called the set-point:
blood pressure,
 blood sugar
 body temperature,
 fluid and electrolyte balance,
 and body weight

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Although this set-point can migrate over
time, from day to day it is remarkably
fixed.
Receptors and Effectors
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*To achieve this task, the hypothalamus
must:
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nerve fibers/endings called receptors/sensors
receive inputs about the state of the body
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effectors are nerve endings that respond to
changes in nerve fibers
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i.e. if anything drifts out of whack.
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i.e. Feedback Loop (more about this later)
Intrinsic Receptors
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*The hypothalamus has some intrinsic
receptors, including:
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thermoreceptors (sense degree of hotness
and coldness) and
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osmoreceptors (sense electrolyte balance).
The hypothalamus sends signals to
effectors (nerve endings that respond)
which can control heart rate,
vasoconstriction, digestion, sweating, etc.
*The Brain
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*We will concentrate on FOUR
homeostatic processes:
1.
2.
3.
4.
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thermoregulation
osmoregulation
blood glucose management
waste management
The first two and last two of these
homeostatic processes are closely
interrelated.
*Thermoregulation:
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The process of keeping the body at a
constant temperature.
We are homiotherms (warm blooded).
Heat is constantly produced through
metabolism (25% remains in the body) and
lost (75%)
 If your body is in a hot or cold environment
your body temperature is 37ºC.
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*Thermoregulation:
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Processes affected by temp.
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Body heat depends on metabolic rate
(how the body uses nutrients, activity)
At rest muscles produce up to 30% of our
body heat (brain)
 During exercise, our muscles produce 40X
more body heat than other tissues (only 25%
efficient)
Normal body temp. 98.6ºF or 37ºC

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enzyme function, disease control, metabolic rate
Controlling body temperature

Animals with a large surface area
compared to their volume will lose heat
faster than animals with a small surface
area.
Volume = _______
Volume = _______
Surface area = ______
Surface area = ______
Volume : Surface area
ratio = ___________
Volume : Surface area
ratio = ___________
Controlling body temperature
Volume : Surface area
1:6
For every 1 unit
of heat made,
heat is lost out
of 6 sides
Volume : Surface area
1:5
For every 1 unit
of heat made,
heat is lost out
of 5 sides
Controlling body temperature
Volume : Surface area
1:6
Volume : Surface area
1:5
The bigger the
Volume : Surface Area ratio
is, the faster heat will be lost.
Penguins huddling to keep warm
THERMAL RANGES
Professor Alan Hedge, Cornell University, January
2007
SKIN (Shell)
 >45°C (>113°F) Burns
 42°C (108°F) Pain
 40°C (104°F) Uncomfortably hot
 25°C (77°F) Uncomfortably cold
 5°C (41°F) Numbness
 0°C (<32°F) Frostbite
 -0.6°C (<31°F) Skin freezes
BODY (Core)
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>42°C (108°F) Fatal
41°C (106°F) Coma, convulsions
39.5°C (103°F) Upper acceptable limit drowsiness
37°C (98.6°F) normal
35.5°C (96°F) Lower acceptable limit - mental
dullness
34.5°C (94°F) Shivering diminishes - extreme
mental slowness
33°C (91°F) Coma
<33°C (91°F) Deep Coma. Death
27°C (81°F) Heart stops. Death
What mechanisms are there to cool
the body down?
Sweating
1.
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When your body is hot, sweat glands under
the skin are stimulated to release sweat.
The liquid sweat turns into a gas (it
evaporates)
To do this, it needs heat.
It gets that heat from your skin.
As your skin loses heat, it cools down.
Sweating
The
skin
What mechanisms are there to cool
the body down?
2.
Vasodilation/Vasoconstriction
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Your blood carries most of the heat energy
around your body.
There are capillaries underneath your skin
that can swell/dilate if you get too hot.
This brings the blood closer to the surface
of the skin so more heat can be lost.
This is why you look red when you are hot!
This means more heat is lost from the surface of the skin
If the
temperature
rises, the blood
vessel dilates
(gets bigger).
What mechanisms are there to warm
the body up?
1.
Vasoconstriction
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This is the opposite of vasodilation
The capillaries underneath your skin get
constricted/shrink (shut off).
This takes the blood away from the surface
of the skin so less heat can be lost.
This means less heat is lost from the surface of the skin
If the temperature
falls, the blood
vessel constricts
(gets shut off).
What mechanisms are there to warm
the body up?
2.
Piloerection
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This is when tiny muscles in the skin contract,
causing the hairs on your skin “stand up” .
It is sometimes called “goose bumps” or
“chicken skin”!
The hairs trap a layer of air next to the skin
which is then warmed by the body heat
The air becomes an insulating layer.
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OSMOREGULATION:
Water Regulation
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Water makes up ~60% of total body
composition, of this.
Water is constantly required and removed.
73% of lean body mass (LBM) is composed
of water
 essential for survival
 required for all cell functions
 used for thermoregulation*
 major component of blood volume
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OSMOREGULATION
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Not enough water in the body –
dehydration.
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In dehydrated states, water is lost from the
blood, electrolyte imbalance
Too much water in the body – edema
(water retention swelling), electrolyte
imbalance
Homeostasis of Heat and Water
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Body temp. monitored by the
hypothalamus.
Skin surface:
32 000 heat receptors/sq. inch
 concentrated in fingertips, nose, elbows,
upper lip, & chest.
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Brain and blood vessels contain the
thermal receptors for sensing core body
temperature
Heat Loss Mechanisms at Rest
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Radiation – at rest 60% of heat loss from
a nude body
Convection: air movement past body.
Two ways, natural (air molecules) and
forced (eg. Fan) (up to 30% lost through
head and neck)
Evaporation: water loss through skin
15% of heat loss
Heat Loss Mechanisms at Rest
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Inhalation/Exhalation: 10% loss of heat
and water loss (exhalation)
Conduction: skin contact with objects
such as chairs, floors, etc. about 3%
Excretion of urine and feces, both
water (major component, 400 – 800
mL/event) and heat loss (3%)
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Winter survival
SWEAT BASICS:
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Each sq. inch of skin has 32 000 nerve
fibers, 98 sebaceous glands & ~650 sweat
glands
Heat and emotions affect sweating
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Emotional tears are more toxic - healing
Men sweat 50% more than women. Older
people (esp males) and children sweat
ineffectively
SWEAT BASICS:
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Eccrine glands produce sweat
99% water
 NaCl
 Other electrolytes
 traces of urea, lactic acid,
fatty acids and proteins
 Colorless and odorless
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http://www.sweathelp.org/English/PFF_Hyperhidrosis_O
verview.asp
SWEAT BASICS:
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Eccrine glands produce
between 200 ml – 10 L per day depending on
activity level and climate
 200 ml/hr at room temperature, and up to 1.5
L/h in extreme heat climates
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The greatest number of sweat glands are
on the forehead, neck, back of hand,
forearm, back and front trunk; lowest on
thighs, soles of feet, & palms of the
hands.
Sweat Glands
E – Epidermal Layer
D - Dermis
H – Hair Follicles
G – Sweat/Eccrine
Glands
S – Sebaceous
Glands
http://www.nature.com/milestones/skinbio/images/subject_index
_02.gif
http://vrc.belfastinstitute.ac.uk/resources/skin/skin.htm
Hair Follicle
SWEAT BASICS:
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Apocrine gland/ducts (sebaceous
glands)
Secrete protein, oils and water. These open
onto hair follicles
 Highest density in underarms, nipples, pubic
area, lips, chin and head, eyelids, outer ear.
 Bacteria decompose apocrine secretions
(within an hour) and create individually
characteristic “body odor” (BO)
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Sweat & Exercise
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High intensity exercises or exercises
lasting more than 1 h can result in 2.0 L/h
of water loss (usually 1.0 L/h is more
common).
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This depends on environmental
conditions, humidity, clothing, intensity,
fitness level, and acclimation to climate.
Sweat & Exercise
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24 h prior to major activity:
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consume fruits, veggies, and carbs to
promote hydration.
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Avoid, caffeines, alcohols (which promote
dehydration).
Sweat & Exercise
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2 h before - 2 cups of water (not juice/pop)
during – more water about every 15
minutes.
After (if over 1 hr) – replace electrolytes
(ie Gatorade which balances sugars, NaCl,
and K ions lost through sweating).
 Make your own – salt, fruit juice, water
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Other ways we lose heat and water:
Expectoration (cough)
Sternutation (sneeze)
Salivation
Ejaculation
Menstruation
Parturition (Birth)
Lactation
Epilation (hair loss)
Lacrimation (tears)
Eructation (burps)
Flatulation
Regurgitation
Spontaneous exanguination (blood loss)
Sweat Gland Video clip (20 sec)
http://www.britannica.com/EBchecked/topic/453087/perspira
tion
What Causes Prickly Heat
Negative Feedback Loop
Control Center (Hypothalamus)
Sensor/Receptor:
Change:
Effector:
Change:
Cause:
Normal Condition:
http://wps.aw.com/bc_martini_eap_5/105/27046/6923809.cw/index.html
Controlling Glucose levels
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Your cells also need an exact level of
glucose in the blood.
Excess glucose gets turned into glycogen
in the liver
Regulated by two pancreatic hormones:
Insulin
 Glucagon
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http://dtc.ucsf.edu/types-of-diabetes/type1/treatment-of-type-1-diabetes/how-the-bodyprocesses-sugar/controlling-blood-sugar/
Glycogen
Too much
glucose in the
blood – Insulin
converts some
of it to
glycogen
Glucose in the blood
Glycogen
Not enough
glucose in
the blood –
glucagon
converts
some
glycogen into
glucose.
Glucose in the blood
Diabetes
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Some people do not produce enough
insulin.
When they eat food, the glucose levels in
their blood cannot be reduced.
This condition is known as DIABETES.
Diabetics sometimes have to inject insulin
into their blood. They have to be careful of
their diet.
Glucose
Concentration
Glucose levels
rise after a meal.
Insulin is
produced and
glucose levels
fall to normal
again.
Normal
Time
Meal eaten
Glucose
Concentration
Glucose levels
rise after a meal.
Diabetic
Insulin is not
produced so
glucose levels
stay high
Time
Meal eaten
The glucose in the
blood increases.
Glycogen
But there is no
insulin to convert it
into glycogen.
Glucose
concentration rises
to dangerous
levels.
Glucose in the blood
Blood Sugar Feedback Loop
Liver
Glycogen
Glucagon
Insulin
Blood
Glucose
http://dtc.ucsf.edu/types-of-diabetes/type1/treatment-of-type-1diabetes/how-the-body-processes-sugar/the-liver-blood-sugar/
Osmoregulation
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Control of water levels
Carried out by the KIDNEYS.
Closely linked to the excretion of urea.
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Waste product made when the LIVER breaks
down excess proteins
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Why might you have to get up to go the washroom
at night if you had a late night steak?
Contains Nitrogen.
The kidneys
•
•
•
•
•
“Cleans” the blood of waste products
Controls water retention
Waste products and water make up urine
• excreted via the ureter.
“Dirty” blood enters the kidney through
renal artery and exits through renal vein
Several things happen to clean the blood...
1. Filtration
Blood enters the tubule area in a
capillary.
The capillary forms a small
“knot” near the kidney tubule
(glomerulus – more about this
later).
The blood is filtered so all the
small particles go into the tubule.
The capillary then carries on to
run next to the tubule.
The kidney tubule now contains
lots of blood components
including:
Glucose:
Ions:
Water:
Urea:
2. Reabsorb sugar
The body needs to have sugar in
the blood for cells to use in
respiration. So all the sugar is
reabsorbed back into the
capillary.
2. Reabsorb sugar
The body needs to have sugar in
the blood for cells to use in
respiration. So all the sugar is
reabsorbed back into the
capillary.
3. Reabsorb water
Water and ions are the next to
be absorbed. It depends on how
much is needed by the body.
3. Reabsorb water
Water and ions are the next to
be absorbed. It depends on how
much is needed by the body.
Reabsorbing water
If you have too little
water in your blood,
you will produce
very concentrated
urine.
If you have too
much water in your
blood, you will
produce very dilute
urine.
(very little water in it
because most was
reabsorbed)
(lots of water in it)
5. Excrete the waste
Everything that is left in the
kidney tubule is waste:
•All the urea
•Excess water
This waste is called urine. It is
excreted via the ureter and is
stored in the bladder.
Renal vein
The “clean” blood leaves the
kidney in the renal vein.
Ureter
Summary of urine production
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Urea is a waste product made in the LIVER.
Water content of the body is controlled in
the KIDNEYS.
Urea, water and other waste makes up
URINE.
Urine travels down the URETER and is
stored in the BLADDER.
Urine is excreted through the URETHRA.