Transcript 01-Homeostasis and Thermoregulation

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Homeostasis
 homeostasis – constant physiological adjustments of
the body in response to external environment
changes
 also known as dynamic equilibrium
What happens to your body when you exercise?
Exercise and Homeostasis
 body temperature
increases
 evaporation of sweat to
cool off
 O2 levels being used up  heart rate increases to
increase blood flow (to get
O2 levels back up)
 increased cellular
metabolism
 pancreas signals breaking
down of biomolecules to
get energy needed to
exercise
Homeostatic Control System
1.
Receptor – organs that detect changes or sense
when conditions are not within “normal” range
2.
Control Centre – organs which process
information it receives from the receptor and send
signals to another part of the body
3.
Effector – coordinating centre sends signals to an
organ / tissue which will normalize the original
organ
dynamic equilibrium
Response
No heat
produced
Analogy
Heater
turned
off
Room
temperature
decreases
Too
hot
Set
point
Too
cold
Set
point
Set point
Control center:
thermostat
Room
temperature
increases
dynamic equilibrium
Heater
turned
on
Response
Heat
produced
Feedback Systems
 negative feedback system - buildup of the end product of
the system shuts the system off
blood pressure drops
blood pressure
rises
brain
nerve pathway
heart rate
increases
arteries
constrict
 The response counteracts further change in the same direction
Feedback Systems
 positive feedback (feed-forward) system - a change in
some variable that triggers mechanisms that amplify the
change
progesterone
decrease
increased
contractions
uterus
oxytocin
endocrine system
Thermoregulation
 Process by which animals maintain an internal
temperature within a tolerable range.
 Critical to survival because biochemical and
physiological processes are sensitive to changes in
temperature.
 Enzymatic reactions
 Properties of membranes
Modes of Heat Exchange
Radiation is the emission of electromagnetic
waves by all objects warmer than absolute
zero. Radiation can transfer heat between
objects that are not in direct contact, as when
a lizard absorbs heat radiating from the sun.
Evaporation is the removal of heat from the surface of a
liquid that is losing some of its molecules as gas.
Evaporation of water from a lizard’s moist surfaces that
are exposed to the environment has a strong cooling effect.
Convection is the transfer of heat by the
Conduction is the direct transfer of thermal motion (heat)
movement of air or liquid past a surface,
as when a breeze contributes to heat loss
from a lizard’s dry skin, or blood moves
heat from the body core to the extremities.
between molecules of objects in direct contact with each
other, as when a lizard sits on a hot rock.
Balancing Heat Loss and Gain
1. Insulation
2. Circulatory Adaptations
3. Cooling by Evaporative Heat Loss
4. Adjusting Metabolic Heat Production
Insulation
 Feathers, hair or fat layers
 Reduces the flow of heat between an animal and its
environment
 Lowers the energy cost of keeping warm
 In mammals, the insulating material is associated
with the integumentary system (skin, hair and
nails)
Hair
Epidermis
Sweat
pore
Muscle
Dermis
Nerve
Sweat
gland
Hypodermis
Adipose tissue
Blood vessels
Oil gland
 Most land animals and birds react to cold by raising
their fur or feathers
 Traps a thicker layer of air
 Increasing its insulating power (the more still air =
more insulation!)
Goosebumps
 Raise hair on our body
 Inherited from our furry
ancestors
 We rely more on a layer
of fat just beneath the
skin
Circulatory Adaptations
 We can alter the amount of blood (and hence heat)
flowing between the body core and the skin.
Vasodilation
Muscles in superficial blood
vessels relax
Increases the diameter of
vessels = more blood
Increases heat transfer,
releasing heat energy to
surroundings.
Vasoconstriction
 Muscles in superficial blood vessels contract
 Smaller diameter of blood vessels = less blood
 Reduces heat transfer, preventing heat loss
 Keeps blood (and heat) in interior of body where it is
needed
Evaporative Heat Loss
 When environmental temperatures are above body
temperature animals
 Sweat, pant, bathe, spread saliva over body surfaces
 Heat is carried away with water molecules as they
change into a gas
Adjusting Metabolic Heat Production
 Shivering and Moving - Heat
production is increased by muscle
activity
 Non-shivering Thermogenesis
(NST) - Certain hormones can
cause mitochondria to increase their
metabolic activity and produce heat
instead of ATP
 Brown Fat – Specialized tissue for
rapid heat production (has higher
conc’n of mitochondria)
What regulates our temperature?
 Hypothalamus - contains a group of nerve cells
that function as a thermostat
Increased body
temperature (such
as when exercising
or in hot
surroundings)
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Cold Response
Homeostasis:
Internal body temperature
of approximately 36–38°C
Body temperature
increases;
thermostat
shuts off warming
mechanisms.
Decreased body
temperature
Vasoconstriction, diverting
blood from skin to deeper tissues
and reducing heat loss
from skin surface.
Skeletal muscles
rapidly contract,
causing shivering,
which generates
heat.
Thermostat in
hypothalamus
activates
warming
mechanisms.
Heat Response
Thermostat in
hypothalamus
activates cooling
mechanisms.
Sweat glands secrete
sweat that evaporates,
cooling the body.
Vasodilation,
Blood vessels
relax and fill
with warm blood;
heat radiates from
skin surface.
Increased body
temperature
Homeostasis:
Internal body temperature
of approximately 36–38°C
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Extreme Cold
Why does your body allow you to get frost bite?
Why is hypothermia such a concern?
Classwork/Homework
 Section 7.1 – Pg. 337 #1-5, 7-9
 Section 7.2 – Pg. 341 # 1-9,11