Section 38.5 (Exam 3) Flashcards
Body Temperature Is Regulated through Adaptations for Heat Production and Heat Loss
How is metabolic rate measured?
consumption of O2 or production of CO2
Describe the metabolic rate of endotherms in the thermoneutral zone.
Metabolic rate of endotherms is low and independent of temperature
What is the basal metabolic rate (BMR)?
Metabolic rate of a resting animal at a temperature in the thermoneutral zone
What is BMR correlated with?
body size and environmental temperature; larger animals have a higher BMR
How does BMR per gram of tissue change with body size?
increases as animals get smaller
Why does BMR per gram of tissue increase as animals get smaller?
The larger SA:V ratio means that smaller animals lose heat quicker, and need to increase their metabolic rate to maintain body temperature
What is the effect of bigger animals having a smaller surface area to volume ratio?
They have less capacity to dissipate heat
Why may large animals have evolved to have a lower BMR?
To prevent overheating, their lack of surface area makes it difficult to lose heat
Why do larger animals have more metabolically inactive support tissue like bone and skin?
Because if their support tissue was too metabolically active, they would overheat
An endotherm’s thermoneutral zone is bounded by critical temperatures. What is the meaning of these temperatures?
Beyond these bounds, temperature regulation would require metabolic energy expenditure
How do endotherms respond to the cold?
increasing metabolic heat production to compensate for heat loss
What are two examples of endotherms increasing metabolic heat production in response to the cold?
Shivering (when these muscles contract, ATP is converted to ADP, producing heat) increases muscle tone
These body movements also contribute to heat production
Thermogenin in brown fat breaking down fat and glucose to create heat
What is brown fat?
A type of fat in mammals that produces heat
Brown fat has abundant mitochondria and blood supply
What is the function of the protein thermogenin?
heat release without any ATP production in the cells by breaking down fat and glucose
Where is brown fat found?
Newborn mammals
Hibernating mammals
Adult humans have some, and its metabolic activity is stimulated by cold exposure
What type of adult humans have more or less brown fat?
Obese people tend to have less brown fat than lean people
What are 4 endotherm adaptations to reduce heat loss (for cold climates)?
Smaller surface area-to-volume ratio, e.g., round body shapes and short appendages
Thermal insulation—fur, feathers, and short appendages
Ability to decrease blood flow to non insulated skin by constricting blood vessels
Countercurrent heat exchange in blood flow to appendages
What are 4 endotherm adaptations for hot climates?
- Increased blood flow to the skin(heat loss), shade-seeking, decreasing activity levels
- Increased surface area for heat dissipation (e.g., jackrabbit ears)
- Large mammals have little or no insulating fur and seek water to wallow in—water has heat absorbing capacity
- Evaporation of water by sweating or panting to dissipate heat
What problem can panting or sweating lead to in hot and arid climates?
water loss
Why does the metabolic rate increase when the upper critical temperature is exceeded?
panting and sweating are active processes that generate heat
What is the main thermoregulatory center in mammals?
hypothalamus
What does cooling the hypothalamus cause?
restriction of skin blood vessels and increases in metabolic heat production
What is hypothermia?
below-normal body temperature
What can unregulated hypothermia be caused by?
starvation, extreme cold, illness, or anesthesia
Many birds and mammals use regulated hypothermia to survive cold periods and food scarcity. What are two examples of regulated hypothermia?
Daily torpor and hibernation
What is daily torpor?
Daily bouts of regulated hypothermia
Small endotherms such as hummingbirds lower body temperature and metabolic rate during inactive periods to conserve energy
What is hibernation?
lasts for days or weeks; metabolic rate drops and body temperature falls close to ambient (even near freezing) temperatures
