1

Controlling the Internal

Environment I - Regulation of

Body Temperature

Keywords (reading p. 925-930)

• 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

http://www.youtube.com/watch?v=ZgTTUuJZAFs

http://www.youtube.com/watch?v=ZvrJgGhnmJo

Frozen tree frog

• http://www.youtube.com/watch?v=Fjr3A_k

fspM

2

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 bilayerhttp://www.youtube.com/watch?v=ULR79TiUj80&feature=related

http://www.youtube.com/watch?v=mbcWGU8fpxA

http://www.youtube.com/watch?v=0ekfkxwl5bQ

Structure of an unsaturated

phospholipid

3

Bilayer with unsaturated

phospholipid stays fluid at lower

temperatures

Maintaining membrane fluidity at

different temperatures

Melting temperatures of some

saturated fatty acids

Name symbol melting T (°C)

Lauric 12:0 44.2

Myristic 14:0 53.9

Stearic 20:0 69.6

Melting temperature of some

unsaturated fatty acids

Name symbol melting T

Palmitoleic 16:1 -0.5

Oleic 18:1 13.4

Linoleic 18:2 -5.0

Linolenic 18:3 -11.0

Fatty acid composition of

membranes from animals

acclimated to different

temperatures

Ratio of saturated to unsaturated

saturated/unsaturated

Class arctic sculpin rat

0°C 37°C

Choline 0.59 1.22

Ethanolamine 0.26 0.65

Serine/inositol 0.48 0.64

4

Ratio of saturated to unsaturated

Class goldfish goldfish

5°C 25°C

Choline 0.66 0.82

Ethanolamine 0.34 0.51

Serine/inositol 0.46 0.63

Regulation of desaturase activity

• Desaturase is a membrane associated

protein

• Under high temperature conditions, high

fatty acid saturation

• Under low temperature, increased

unsaturation

Desaturase in Tetrahymena

• Phospholipids are constantly cycled into the

lipid bilayer.

• Exposed desaturase will form unsaturated

PLs that will then go into bilayer increasing

fluidity

The making of whipped cream and

butter

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

5

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 Brandt's Cormorants, Phalacrocorax

penicillatus, taking advantage of

coastal morning sunlight.

6

Example of

physiological:

countercurrent

heat exchange

http://www.youtube.com/wat

ch?v=TMCf7SNUb-Q

• 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

7

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 circuited

mitochondria 5% in human infants

Brown fat White fat

8

Insect preflight warmup

http://www.youtube.com/watch?v=_WP2XwBhmAk

http://www.youtube.com/watch?v=BQ5bEdTZgds&feature=related

http://www.youtube.com/watch?v=QsYFpIYaty4

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)

• thermal camera shows how difficult it is to

be a little seal in the Antarctic. The larger

red image is the mother seal who is

followed by her little blue pup. Blue

represents cold temperatures; red and

orange are warm areas. Mom with her thick

blubber layer appears much warmer than

her new born pup.