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 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 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
Body surface 7 12 17 22 27 5 10 15 20 25 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)