CONTROLLING
THE
INTERNAL
ENVIRONMENT
Volunteer State Community College
Nancy G. Morris
Campbell: Chapter 44
Control the Internal Environment
 Most animals can survive
environmental fluctuations more
extreme than any individual cell
could tolerate…
 because mechanisms of homeostasis
maintain internal environments within
ranges tolerable to body cells.
Mechanisms of homeostasis:
 Adaptation to the thermal environment:
thermoregulation
 Adaptation to the osmotic environment:
osmoregulation
 Strategies for the elimination of waste
products of protein catabolism:
excretion
Regulation of Body Temperature
 Metabolism & membrane properties are
very sensitive to changes in an animal’s
internal temperature.
 Each animal lives in, and is adapted to,
an optimal temperature range in which it
can maintain a constant internal
temperature when external temperatures
fluctuate.
 Maintaining the body temperature within
a range that permits cells to function
efficiently is known as thermoregulation.
4 physical processes account for heat
gain or loss:
 1) Conduction
 2) Convection
 3) Radiation
 4) Evaporation
Evaporation & convection are the
most variable causes of heat
loss.
4 physical processes account for heat
gain or loss:
 Conduction is the direct transfer of heat
(thermal motion) between molecules of
the environment & body surface.
– Heat is always conducted from a body of
higher temperature to one of lower
temperature.
– Water is 50 to 100 times more efficient
than air in conducting heat.
– On a hot day, an animal in cold water cools
more rapidly than one on land.
4 physical processes account for heat
gain or loss:
 Convection is the transfer of heat
by movement of air or liquid past
a body surface.
– For example, breezes contribute to
heat loss from an animal with dry
skin.
4 physical processes account for heat
gain or loss:
 Radiation is the emission of
electromagnetic waves
produced by all objects
warmer than absolute zero.
– It can transfer heat between
objects not in direct contact.
– For example, an animal can be
warmed by the heat radiating
from the sun.
4 physical processes account for heat
gain or loss:
 Evaporation is the loss of heat from a
liquid’s surface that is losing some
molecules as gas.
- Production of sweat greatly increases
evaporative cooling
- Can only occur if surrounding air is not
saturated with water molecules.
Major source of heat?
 Ectotherms derive body heat mainly
from their surroundings
– Invertebrates, fishes, reptiles, amphibians
 Endotherms derive heat mainly from
metabolic activity
– Mammals, birds, some fishes, numerous
insects
Thermoregulation:
 Involves physiological and behavioral
adjustments.
 Heat loss is reduced by presence of hair,
feathers, and fat just below the skin.
 The amount of blood flowing to the skin
can be changed to regulate heat
exchange: vasodilation and
vasoconstriction.
 Evaporative heat loss: panting, sweating,
bathing increases evaporative cooling
across the skin.
Behavioral Responses
 In winter, many animals bask in
the sun or on warm rocks.
 In summer, many animals burrow
or move to damp areas.
 Some animals migrate to more
suitable climates.
Metabolic heat production
 Occurs only in birds and mammals
 Increased muscle activity and
shivering can greatly increase
metabolic heat produced.
Water Balance & Waste Disposal
 The majority of cell in most animals (all but
sponges and cnidarians) are not exposed to
the external environment, but are bathed by
an extracellular fluid.
 Animals with an open circulatory system have
an extracellular compartment containing
hemolymph which bathes the cells.
 Animals with a closed circulatory system have
two extracellular compartments – interstitial
fluid and blood plasma.
Nitrogenous Wastes
 The metabolism of proteins and
nucleic acids produces ammonia, a
small & very toxic waste product.
 Some animals excrete the
ammonia directly, while other
convert it to urea or uric acid,
which are less toxic, but require
ATP to produce.
Nitrogenous Wastes:
Ammonia:
 water soluble and permeates
membranes easily.
 produced by aquatic animals.
 In soft-bodied invertebrates,
ammonia diffuses across the body
surface and into the surrounding
water.
 In fishes, ammonia is excreted as
ammonium ions across gill
epithelium.
Nitrogenous Wastes:
Urea
 Terrestrial animals can not excrete ammonia
because it requires large amounts of water and
is so toxic it must be eliminated quickly.
 Mammals & adult amphibians
 Can be concentrated because it is 100,000
times LESS toxic than ammonia.
 Reduces water loss for terrestrial animals.
 Liver combines CO2 with amine groups to
produce urea. Filtered out by kidneys.
Nitrogenous Wastes:
Uric Acid
 Land snails, insects, birds, and many
reptiles.
 Much less water soluble than urea or
ammonia; can be excreted as a precipitate
after reabsorption of water from urine.
 Eliminated through cloaca in paste form
(mixed with feces) in birds & reptiles.
 Because it precipitates out, it can be
stored as a solid in the egg without toxic
build up.
Nitrogenous
Wastes
Osmotic gain and water loss:
•Animal cells can not survive a net gain or
a loss of water.
•Osmosis – diffusion of water
•Occurs when two solutions separated by
a membrane differ in osmolarity (total
solute concentration)
•In other words, there is a concentration
difference.
Osmoregulators expend energy
 Osmoregulators expend energy to control
their internal osmolarity.
 Water may enter a terrestrial organism
through food, drinking, oxidative
phosphorylation; water may exit through
excretion and evaporation.
 Aquatic organisms are not affected by
evaporation but face a major osmotic
problem: water may enter (in fresh
water) or leave (in marine water) the
body.
Excretion
 process by which metabolic
wastes are eliminated
 urine, sweat, CO2, nitrogen
are primary wastes
 3 excretory functions:
– Nitrogen Excretion
– Osmotic Regulation
– Water Balance
Nitrogen Excretion
 nitrogenous waste results from
deamination of amino acids during
protein catabolism
 packaged as urea by liver
 filtered out by kidneys
Excretion
OSMOTIC REGULATION
(regulation of salt, ions, solutes)

fluid and electrolyte
homeostasis

WATER BALANCE
(maintenance)
Major fluid compartments:
 PLASMA COMPARTMENT
– Blood plasma
–
 INTERSTITIAL COMPARTMENT
– Bathing tissues & returning to blood
 INTRACELLULAR FLUID
– Inside cell
What goes where?
Approximately 2,300 mL H2O absorbed per
day by the small intestine
 Approximately 300 mL per day lost from the
lungs
 Approximately 1500 mL per day lost from the
kidneys
 Approximately 500 mL per day lost from the skin
Water sources:
 Principle source is diet.
 Oxidation of nutrient molecules
during aerobic respiration. Why?
Form follows function (again):
 Excretory structures vary based on the
type of osmotic environment in which the
animal lives.
 TERRESTRIAL ANIMALS need to
conserve water so …
 Reptiles & birds excrete nitrogenous
wastes as crystalline uric acid.
 Mammals excrete urea that must be
dissolved in water (urine).
Osmoregulation in Fishes:
Survey of the phyla:
 CONTRACTILE VACUOLES
sponges
 PROTONEPHRIDIUM – (44.15)
platyhelminthes & nematodes
 METANEPHRIDIUM – (44.16)
annelids
 MALPHIGIAN TUBULES – (44.17)
arthropods
 NEPHRIDIUM – (44.18)
mammals
Survey of the phyla:
PROTONEPHRIDIUM
platyhelminthes & nematodes
 flame-bulb system
 wastes either diffuse out of
body or are excreted into the
gastrovascular cavity
 cilia keeps fluid moving though
the tubules
Survey of the phyla:
METANEPHRIDIUM annelids
 coelom is fluid-filled
 each tubule possesses a nephrostome,
collecting tubule, and a nephridiopore
 nephrostome drains the metamere
just anterior to the one in which the
metanephridium is located
 cilia keeps fluid moving though the
tubules
Metanephridium:
Survey of the phyla:
Malphigian tubules – arthropods
 outfoldings of the digestive system.
 tubules secrete nitrogenous wastes
and salts from the hemolymph; water
follows the solutes by osmosis.
 most of the water and salts are
reabsorbed across the epithelium in
the rectum.
 dry product called frass is eliminated.
Malpighian Tubules:
Major organs:
Kidneys
Ureters
Bladder
Urethra
Aorta & Posterior Vena Cava
Renal arteries & renal veins
Human Excretory System:
Anatomy:
The Kidney:
 Ureter
 Renal pelvis
– Collecting ducts
 Renal medulla
– Loop of Henle
– Collecting Ducts
 Renal cortex (bark)
– Bowman’s capsules
– Prominal & distal tubules
Human Excretory System:
Anatomy of a Nephron:
 Glomerulus
 Afferent & efferent arteriole
 Peritubular capillaries
 Proximal Tubuke
 Loop of Henle – ascending & descending
 Collecting Duct
Human Excretory System:
URINE FORMATION:
 Basic unit of Mammalian Kidney:
– nephron
– 1 million per kidney
– total of 50 miles of tubules
 Involves two sets of capillaries:
– 1) glomerulus
– 2) peritubular capillaries
Human Excretory System
URINE FORMATION:
Four components:
–
–
–
–
1)
2)
3)
4)
filtration
reabsorption
secretion
excretion
Urine Formation
URINE FORMATION:
1) Filtration:
 Filtrate is forced out of glomerulus &
received by Bowman’s capsule.
 Approximately 180 liters per day or
4.5 x the amount of fluid in the body
is forced out into glomerulus.
 = filters 125 mL per minute
URINE FORMATION:
2) Reabsorption:
 Occurs simultaneously with secretion.
 Mostly salts, H2O, solutes, vitamins
are transported back to peritubular
capillaries via active transport.
 124 mL of the 125 mL filtered out
during filtration will be reabsorbed
here.
URINE FORMATION:
3) Secretion:
 Filtrate is passed through the renal
tubule.
 Walls of the tubule are a single cellular
layer of cubodial epithelium specialized
for active transport.
 Molecules remaining in the plasma are
selectively removed (penicillin) from the
peritubular capillaries & secreted into the
filtrate.
URINE FORMATION:
 Na+ Pump – sodium ions are actively
pumped across the membrane and Clfollow passively by electrostatic
attraction.
 Active transport is a “high energy”
requirement – higher on a gram for
gram basis than the heart beat.
URINE FORMATION:
4) Excretion:
 Remaining fluids leave the nephron
and pass into the renal pelvis (funnel
of the ureter) and travel to bladder
until released through the urethra.
The Nephron:
URINE FORMATION:
Normal urine contains:
 1) 95% water
 2) urea
 3) electrolytes – such as
– Na+, Cl-, PO4-, SO4 4) pigments
 5) hormones
URINE FORMATION:
Abnormal Urine contains:
 1) high glucose – diabetes mellitus
 2) RBC’s
 3) WBC’s
 4) proteins
 5) ketone bodies (catabolism of
fatty acids, ketogenesis)
Human kidney concentrates urine: