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uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation
allows its internal condition to vary with certain external changes
Organisms use what to maintain a “steady state” or internal balance regardless of external environment
- In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level
- Mechanisms of homeostasis moderate changes in the internal environment
- For a given variable, fluctuations above or below a set point serve as a stimulus; these are detected by a sensor and trigger a response (in nervous system)
how does a mammal (otter) maintain its body temp in a cold environment (compared to a fish)
- fish's body temp will match environment
- mammal burns calories to maintain its temp
The dynamic equilibrium of homeostasis is maintained by what?
- negative feedback which helps to return a variable to either a normal range or a set point
- Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off
loops occur in animals, but do not usually contribute to homeostasis
Set points and normal ranges can change with what?
age or show cyclic variation
homeostasis can adjust to changes in external environment
is the process by which animals maintain an internal temperature within a tolerable range
animals generate heat by metabolism; birds and mammals are endotherms
animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and non-avian reptiles
In general, who tolerates greater variation in internal temperature
The body temperature of a poikilotherm does what?
varies with its environment
a hometherm does what?
is relatively constant compared to a poikilotherm
- are active at a greater range of external temperatures
- Endothermy is more energetically expensive than ectothermy
what are the 4 physical processes organisms use to exchange heat?
Organisms exchange heat by four physical processes: conduction, convection, radiation, and evaporation
Heat regulation in mammals often involves the what system?
- integumentary system
- skin, hair, and nails
what 5 adaptations help animals thermoregulate?
- Five general adaptations help animals thermoregulate:
- –Circulatory adaptations
- –Cooling by evaporative heat loss
- –Behavioral responses
- –Adjusting metabolic heat production
is a major thermoregulatory adaptation in mammals and birds
skin, feathers, fur and blubber reduce what?
Skin, feathers, fur, and blubber reduce heat flow between an animal and its environment
feathers were used for thermoregulation before they were used for flight
- blood flow in the skin increases, facilitating heat loss
- Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin
blood flow in the skin decreases, lowering heat loss
Alcohol is a what?
- –Blood vessels on the surface are dilated
- –Apparent warmth caused by this
- –Actual effect is to cool the body
- The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange
- Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions
- Countercurrent heat exchangers are an important mechanism for reducing heat loss
- Many types of animals lose heat through evaporation of water in sweat
- Panting increases the cooling effect in birds and many mammals
- Sweating or bathing moistens the skin, helping to cool an animal down
- Both endotherms and ectotherms use behavioral responses to control body temperature
- Some terrestrial invertebrates have postures that minimize or maximize absorption of solar heat
cyclic movement often timed with the seasons
endotherm behavior (grey whale)
- Gray whales
- –Summer in the Arctic
- –Migrate to the Baja Peninsula for calving
Birds and mammals can vary their what to acclimatize to seasonal temperature changes
When temperatures are subzero, some ectotherms produce what kind of compounds to prevent ice formation in their cells
Surface Area to Volume ratio for endotherms
- – increases as the square of the animal’s length
- – increases as the cube of the animal’s length
what region of the brain controls thermoregulation
The hypothalamus triggers what?
- heat loss or heat generating mechanisms
- Fever is the result of a change to the set point for a biological thermostat
is the amount of energy an animal uses in a unit of time
Basal metabolic rate (BMR)
is the metabolic rate of an endotherm at rest at a “comfortable” temperature
Standard metabolic rate (SMR)
- is the metabolic rate of an ectotherm at rest at a specific temperature
- (BMR and SMR)Both rates assume a nongrowing, fasting, and nonstressed animal
- Ectotherms have much lower metabolic rates than endotherms of a comparable size
- is a physiological state in which activity is low and metabolism decreases
- Torpor enables animals to save energy while avoiding difficult and dangerous conditions
- is long-term torpor that is an adaptation to winter cold and food scarcity
- –Glucose is obtained from gluconeogenesis during hibernation