HOMEOSTASIS AND
THERMOREGULATION
CH 40
I. Regulatory systems maintain
homeostasis
A. Why homeostasis?
 In order for cells to function
properly, their internal
environment (pH, temp, amount of
glucose, amount of oxygen) must be
maintained in narrow limits
 Homeostasis is the ability of an
organism to maintain constant
internal conditions
 Any homeostatic control system has
three functional components: a
receptor, a control center, and an
effector.
o The receptor detects a change in
some variable in the animal’s
internal environment, such as a
change in temperature.
o The control center processes the
information it receives from the
receptor and directs an
appropriate response by the
effector.
B. Negative feedback loops and
homeostasis
Signal that organism is out of
homeostasis triggers events to drive
organism back to homeostasis
C. Positive feedback loops
 Signal that organism is out of
homeostasis causes organism to go
farther away from homeostasis yet
end result returns organism to
homeostasis
Ex: Childbirth
 During labor, signals from the
brain stimulate uterine contractions
 The pushing of the fetus on the
uterine opening sends a signal to
the brain to continue signaling
uterine contractions
 This causes fetus to be expelled
bringing mother back to
homeostasis
II. Thermoregulation
A. Types of animals
1. Ectotherms
 Maintain body temp from its
surroundings (fish, amphibians,
reptiles)
o Vertebrate ectotherms that live on
land must change locations to
regulate body temp
o Vertebrate ectotherms that live in
water usually don’t need to
change surroundings because
water temp doesn’t fluctuate as
much as air temp. WHY??
2. endotherms
 maintain body temp internally
(mammals and birds)
B. How endotherms maintain body
temperature
Increasing insulation, shedding,
sweating, dilating or constricting blood
vessels, shivering, increased
metabolism, behavioral changes
1. Insulation:
 Hair, fur, feathers, fat layers
 Raised fur and feathers traps heat
near skin
 Excess fat near surface prevents
core body heat loss in marine
mammals
 Oily secretions in many birds and
mammals that spend time in water
prevents heat loss
2. dilating or constricting blood
vessels:
 Vasodilation increases the diameter
of the blood vessels. This increases
vessel surface area and allows
excess heat to be lost
 Vasoconstriction constricts the
diameter of blood vessels. This
decreases vessel surface area and
prevents heat from being lost
3. evaporative cooling:
 Humans lose excess heat thru their
skin (sweating)
 Furry mammals lose excess heat
thru panting.
 This is due to the excess heat
necessary to break H-bonds
between water molecules
4. shivering:
 Increased muscle contractions
generates heat
Shivering vasodilation,
vasoconstriction, sweating is controlled
by the hypothalamus
5. Behavioral changes
 Migration in birds
 hibernation
6. Increases metabolism
 In birds and small mammals
 Increase rate of aerobic respiraton
to generate heat
 these animals have a lot of brown
fat
 the brown fat will break down
glucose YET instead of getting ATP
out of it, they generate heat.
III. Feedback control of
thermoregulation in mammals
 Controlled by the hypothalamus in
the brain
Increase in body temp stimulates
hypothalamus to:
 Cause the dilation of blood vessels
so heat can be released
 Activate sweat glands to induce
evaporative cooling
 The return to normal body temp
negatively feeds back on the
hypothalamus
A decrease in body temp stimulates the
hypothalamus to:
 Constrict blood vessels so less heat
is lost
 Activate skeletal muscles to shiver
to generate heat
 The return to normal body temp
negatively feeds back on the
hypothalamus
http://bcs.whfreeman.com/thelifewire/
content/chp41/41020.html