Internal Regulation
9.1 Temperature Regulation
Homeostasis and Allostasis
Homeostasis = temperature regulation and other biological processes that keep body
variables within a fixed range (resembles thermostat)
➔ a set point is a single value that the body works to maintain
➔ processes that reduce discrepancies from set points are called negative feedback
Allostasis = the adaptive way in which the body anticipated needs depending on the
situation, avoiding error rather than just correcting them (e.g sign of danger => sweat)
Controlling Body Temperature
➔ most of our daily lost calories go to basal metabolism (the energy used to
maintain a constant body temperature while at rest)
➔ amphibians, reptiles, and most fish are ectothermic → depend on external
sources for body heat instead of generating it themselves
➔ mammals and birds are endothermic → generate enough body heat to remain
significantly above the temperature of the environment
a. Surviving in Extreme Cold
➔ ectothermic animals are more vulnerable to extreme cold
➔ their bodies can form ice crystals if temperature falls below freezing point
➔ some can stock their blood with antifreeze chemicals at the start of winter +
mechanisms of avoiding damage from freezing
b. Advantages of Constant High Body Temperature
➔ mammals and birds keep bodies warm in order to stay ready for vigorous activity
➔ temperature above 41 degrees celsius: proteins break bonds and lose properties
➔ reproductive cells require a cooler environment than the rest of the body
c. Brain Mechanisms
Preoptic area/anterior hypothalamus (POA/AH) → the primary area for
controlling mechanisms of controlling temperature regulation; receives input from
temperature receptors in the skin, organs, and hypothalamus; sends output to the
hindbrain’s raphe nucleus (controls autonomic responses such as sweating)
d. Fever
➔ hypothalamus directs the body to produce it in response to infections
➔ certain bacteria grows less vigorously at high temperatures
➔ immune system works better at high temperatures
9.1 Temperature Regulation
Homeostasis and Allostasis
Homeostasis = temperature regulation and other biological processes that keep body
variables within a fixed range (resembles thermostat)
➔ a set point is a single value that the body works to maintain
➔ processes that reduce discrepancies from set points are called negative feedback
Allostasis = the adaptive way in which the body anticipated needs depending on the
situation, avoiding error rather than just correcting them (e.g sign of danger => sweat)
Controlling Body Temperature
➔ most of our daily lost calories go to basal metabolism (the energy used to
maintain a constant body temperature while at rest)
➔ amphibians, reptiles, and most fish are ectothermic → depend on external
sources for body heat instead of generating it themselves
➔ mammals and birds are endothermic → generate enough body heat to remain
significantly above the temperature of the environment
a. Surviving in Extreme Cold
➔ ectothermic animals are more vulnerable to extreme cold
➔ their bodies can form ice crystals if temperature falls below freezing point
➔ some can stock their blood with antifreeze chemicals at the start of winter +
mechanisms of avoiding damage from freezing
b. Advantages of Constant High Body Temperature
➔ mammals and birds keep bodies warm in order to stay ready for vigorous activity
➔ temperature above 41 degrees celsius: proteins break bonds and lose properties
➔ reproductive cells require a cooler environment than the rest of the body
c. Brain Mechanisms
Preoptic area/anterior hypothalamus (POA/AH) → the primary area for
controlling mechanisms of controlling temperature regulation; receives input from
temperature receptors in the skin, organs, and hypothalamus; sends output to the
hindbrain’s raphe nucleus (controls autonomic responses such as sweating)
d. Fever
➔ hypothalamus directs the body to produce it in response to infections
➔ certain bacteria grows less vigorously at high temperatures
➔ immune system works better at high temperatures
