Controlling the Internal Environment I - Regulation of

Body Temperature

Keywords (reading p. 865-873)

• Temperature effects– On reactions

– On lipid bilayer

• Endotherm• Ectotherm• Homeostasis• Thermoregulation• Behavioral

thermoregulation

• Physiological thermoregulation– Countercurrent heat

exchange

– Shivering

– Effect of large size

– insulation

Temperature

• Affects the rates of reactions and the characteristics of macromolecules

• Since organisms are machines made of macromolecules in which chemical reactions occur, temperature is an very important environmental feature

Temperature affects the rates of reactions, e.g. enzyme catalyzed

reaction

Illustrated by gas molecules in a balloon slowing down if they are

cooled

What is the magnitude of temperature effects for

physiological processes or biochemical reactions?

• Increase by 2-3 fold for a 10°C increase in temperature.

• Q10 value = 2 to 3

Q10 values differ for different physiological processes or

biochemical reactions• Some will speed up more, some less

• This can ruin coordination of enzymes and reactions in metabolism, e.g., mitochondria

Temperature affects characteristics of macromolecules

• Example: lipid bilayer

Lipid bilayer

Structure of an unsaturated phospholipid

Bilayer with unsaturated phospholipid stays fluid at lower

temperatures

Since temperature has such a fundamental influence on

biochemistry and physiology, animals:

• A. regulate their body temperatures so they aren’t affected by temperature or can live under a wide range of conditions

• B. Don’t regulate their temperature and accept metabolic consequences or live under small range of conditions

Endotherms vs. Ectotherms

• Ectotherms have a body temperature the same as their environment

• Endotherms use heat from metabolism– When endotherms are able to regulate their

temperature they are called homeotherms

Example of endotherm

and ectotherm

Homeostasis• The steady-state physiological condition of

the body

• Internal fluctuations are small

Thermoregulation

• Regulation of body temperature

• Can be behavioral or physiological

Behavioral thermoregulation

Example of physiological: countercurrent heat exchange

• Arteries and veins in appendages are closely associated

• Hot arterial blood passes heat to returning venous blood.

• No heat is lost

Blood vessels in a bird leg

• Similar mechanism in flippers of marine mammals

• Blood flow can be controlled so that heat is lost. Blood goes to alternate veins close to the surface.

Countercurrent exchange is a trick used by many animals

Tuna heat exchanger

Great white shark

5

10

15

20

25

7

12

17

22

27

Body surface

Body core

Other tricks: shivering

• Non-shivering thermogenesis: brown fat

• Using ATP to contract muscles releasing heat instead of movement

Brown fat

Short-circuiting the mitochondria

Insect preflight warmup

Another trick: reduce heat loss

• Large size - reduced surface area relative to volume prevents heat from escaping

• Insulation - e.g., fur, feathers

• Big problem for marine mammals since they have high body temp. and water conducts heat faster than air

Insulating fat (blubber)