Lecture 20: Thermal Physiology Part 2 (final)

Question 1

What is the key difference between an endotherm and an ectotherm in terms of thermogenesis?
a) Endotherms rely entirely on external heat sources, while ectotherms retain internally generated heat.
b) Endotherms retain heat generated by metabolic processes, while ectotherms rely on external heat sources.
c) Endotherms have no way of dissipating heat, while ectotherms regulate body temperature through sweating.
d) Endotherms and ectotherms both retain heat equally.

Answer 1

Answer: b) Endotherms retain heat generated by metabolic processes, while ectotherms rely on external heat sources.

Question 2

In endotherms, what is the primary physiological function of retaining heat generated by metabolic processes?
a) To increase metabolic rates
b) To elevate body temperature above environmental temperature
c) To prevent sweating and panting
d) To reduce the need for energy metabolism

Answer 2

Answer: b) To elevate body temperature above environmental temperature

Question 3

Where is the “central internal thermostat” located in mammals?
a) Hypothalamus
b) Spinal cord
c) Peripheral sensors
d) Brainstem

Answer 3

Answer: a) Hypothalamus

Question 4

How does the hypothalamus regulate body temperature in mammals?
a) By sensing environmental temperature directly
b) By integrating signals from central and peripheral thermal sensors
c) By controlling behavioral responses exclusively
d) By producing antifreeze proteins

Answer 4

Answer: b) By integrating signals from central (core) and peripheral (hands and feet, skin) thermal sensors

Question 5

How is the central internal thermostat of birds different from mammals?
a) It is more sensitive to peripheral thermal sensors than central ones.
b) It is located in the spinal cord rather than the hypothalamus.
c) Birds do not have a central thermostat.
d) Birds regulate temperature using only external sources.

Answer 5

Answer: b) It is located in the spinal cord rather than the hypothalamus.

Question 6

Which thermal sensors are more critical for regulating body temperature in mammals?
a) Peripheral sensors located in fingers
b) Central thermal sensors located in the core
c) Sensors located in skin only
d) Sensors that detect light levels

Answer 6

Answer: b) Central thermal sensors located in the core

Question 7

What happens when mammals experience a drop in environmental temperature?
a) The hypothalamus sends signals to increase heat dissipation.
b) The hypothalamus sends signals to increase heat production and retention.
c) Central thermal sensors signal peripheral sensors to cool down.
d) The spinal cord activates behavioral thermoregulation.

Answer 7

Answer: b) The hypothalamus sends signals to increase heat production and retention.

Question 8

What does the thermoneutral zone (TNZ) represent in homeotherms?
a) The range of ambient temperatures where metabolic rate is at its maximum
b) The range of ambient temperatures where metabolic rate remains constant
c) The range of body temperatures where heat dissipation occurs
d) The range of temperatures where metabolic rate spikes due to shivering

Answer 8

Answer: b) The range of ambient temperatures where metabolic rate remains constant

Question 9

What happens when the ambient temperature drops below the lower-critical temperature in homeotherms?
a) Metabolic rate decreases to conserve energy.
b) Metabolic rate increases to generate heat.
c) Metabolic rate remains constant to maintain basal levels.
d) Oxygen consumption decreases as heat production stops.

Answer 9

Answer: b) Metabolic rate increases to generate heat.

Question 10

What happens when the ambient temperature rises above the upper-critical temperature in homeotherms?
a) Metabolic rate increases to lose heat through cooling mechanisms.
b) Metabolic rate remains constant, and heat loss is passive.
c) Metabolic rate decreases as oxygen consumption declines.
d) Heat production increases to match ambient temperature.

Answer 10

Answer: a) Metabolic rate increases to lose heat through cooling mechanisms.

Question 11

What term describes the temperature below which metabolic rate begins to increase in homeotherms?
a) Thermoneutral temperature
b) Upper-critical temperature
c) Basal metabolic temperature
d) Lower-critical temperature

Answer 11

Answer: d) Lower-critical temperature

Question 12

How do homeotherms maintain a constant metabolic rate within the thermoneutral zone?
a) By producing antifreeze compounds
b) By adjusting posture and using passive mechanisms like fur or feathers
c) By increasing oxygen consumption
d) By generating heat through shivering

Answer 12

Answer: b) By adjusting posture and using passive mechanisms like fur or feathers

Question 13

What is a potential risk of controlled hypothermia in animals like kangaroo mice?
a) They may overheat due to increased metabolic activity.
b) Predators can more easily catch them when their body temperature is lower.
c) Their oxygen consumption may rise, leading to energy exhaustion.
d) Their body temperature becomes permanently unstable.

Answer 13

Answer: b) Predators can more easily catch them when their body temperature is lower.

Question 14

How does piloerection help reduce heat loss in animals?
a) By increasing blood flow to the skin
b) By trapping motionless air with raised hair or feathers
c) By generating additional metabolic heat
d) By allowing sweat to evaporate more efficiently

Answer 14

Answer: b) By trapping motionless air with raised hair or feathers

Question 15

Which of the following is an example of a behavioral mechanism to retain heat?
a) Piloerection
b) Snake curling into a ball after a meal
c) Sweating
d) Increased blood flow to the extremities

Answer 15

Answer: b) Snake curling into a ball after a meal

Question 16

What is the function of vasomotor response in heat regulation?
a) Increasing metabolic rate to generate heat
b) Regulating blood flow to the skin surface to control heat exchange
c) Producing antifreeze proteins to prevent heat loss
d) Reducing oxygen consumption to conserve energy

Answer 16

Answer: b) Regulating blood flow to the skin surface to control heat exchange

Question 17

What happens to arterioles under cold environmental temperatures?
a) They constrict to reduce blood flow to the skin surface.
b) They dilate to increase heat loss through the skin.
c) They constrict to increase blood flow to the extremities.
d) They bypass the AV shunt to retain heat.

Answer 17

Answer: a) They constrict to reduce blood flow to the skin surface.

Question 18

What is the role of the arteriovenous (AV) shunt in heat regulation?
a) It promotes heat retention by directing blood flow away from the skin surface.
b) It dilates to allow more blood flow to the skin during high body temperatures.
c) It decreases sweating to conserve water in dry environments.
d) It regulates metabolic rate during extreme temperatures.

Answer 18

Answer: a) It promotes heat retention by directing blood flow away from the skin surface.

Question 19

How does sweating reduce body temperature?
a) By increasing metabolic activity
b) By trapping a layer of still air near the skin
c) By utilizing evaporative cooling as water changes from liquid to gas
d) By decreasing oxygen consumption

Answer 19

Answer: c) By utilizing evaporative cooling as water changes from liquid to gas

Question 20

Which of the following animals primarily relies on evaporative cooling through sweating?
a) Dogs
b) Pigs
c) Large mammals such as humans
d) Fish

Answer 20

Answer: c) Large mammals such as humans

Question 21

What is the vasomotor response, and how does it contribute to heat regulation in animals?

a) A response that involves constriction or dilation of blood vessels to regulate blood flow to the skin surface for heat exchange.
b) A behavioral mechanism where animals curl up to reduce heat loss.
c) A biochemical process involving the production of antifreeze proteins to retain heat.
d) A metabolic response where the body increases oxygen consumption to generate heat.

Answer 21

Answer:
a) A response that involves constriction or dilation of blood vessels to regulate blood flow to the skin surface for heat exchange.

Question 22

How does panting increase heat loss in animals?
a) By increasing blood flow to the extremities
b) By promoting convection and evaporation across the respiratory surface
c) By increasing the production of antifreeze proteins
d) By trapping heat in the body through reduced metabolic activity

Answer 22

Answer: b) By promoting convection and evaporation across the respiratory surface

Question 23

Why don’t animals experience respiratory alkalosis during panting?
a) Because they restrict airflow to their lower airways where gas exchange occurs
b) Because panting increases CO₂ levels in the blood
c) Because they increase ventilation frequency without reducing tidal volume
d) Because they breathe air out of their lungs directly into the bloodstream

Answer 23

Answer: a) Because they restrict airflow to their lower airways where gas exchange occurs

Question 24

Why don’t animals get respiratory alkalosis? (short answer question)

Answer 24

Animals don’t get respiratory alkalosis during panting because they restrict airflow to their upper airways, where there is no gas exchange with the blood. This means the rapid breathing during panting doesn’t lead to significant expulsion of CO₂, which would otherwise disrupt the blood’s CO₂ levels and cause an increase in blood pH. By preventing a drop in CO₂, they avoid the condition known as respiratory alkalosis, where the blood becomes too basic. Instead, panting serves the purpose of increasing heat loss through convection and evaporation without altering the blood gas profile.

Question 25

What is the primary function of shivering thermogenesis?
a) To produce useful mechanical work through coordinated muscle contractions
b) To generate heat through uncoordinated myofiber contractions
c) To conserve energy by slowing metabolic processes
d) To redistribute heat across the body

Answer 25

Answer:
b) To generate heat through uncoordinated myofiber contractions

Question 26

Which of the following animals is capable of shivering thermogenesis?

a) Frogs
b) Birds
c) Lizards
d) Fish
e) mammals
f) b & e

Answer 26

f) b & e

Question 27

Which of the following organisms is likely to exhibit non-shivering thermogenesis through brown adipose tissue (BAT)?

a) Adult birds
b) Newborn placental mammals
c) Amphibians
d) Adult lizards
e) Duckilings

Answer 27

Answer:
b) Newborn placental mammals & e) Ducklings

Question 28

What is the main function of brown adipose tissue (BAT) in mammals?
a) Storing energy for later use
b) Generating heat without muscle contractions
c) Aiding in locomotion
d) Producing ATP for metabolic processes

Answer 28

Answer: b) Generating heat without muscle contractions

Question 29

Which protein is responsible for heat production in brown adipose tissue?
a) Cytochrome c oxidase
b) Thermogenin (UCP1)
c) Myosin
d) Hemoglobin

Answer 29

Answer: b) Thermogenin (UCP1)

Question 30

Non-shivering thermogenesis is most commonly observed in which groups of animals?
a) Reptiles and amphibians
b) Placental mammals and newborns
c) Adult birds and amphibians
d) Fish and invertebrates

Answer 30

Answer: b) Placental mammals and newborns

Question 31

What distinguishes the mitochondria in brown adipose tissue from other tissues?
a) They use oxygen more efficiently
b) They produce heat instead of ATP
c) They lack a mitochondrial membrane
d) They have fewer electron transport chains

Answer 31

Answer: b) They produce heat instead of ATP

Question 32

Describe the difference between coupled and uncoupled mitochondria in terms of energy production and heat generation. How does this relate to the function of brown adipose tissue (BAT)?

Answer 32

Coupled mitochondria generate ATP through oxidative phosphorylation. In this process, protons are pumped into the intermembrane space of the mitochondria, creating a proton gradient. These protons flow back into the mitochondrial matrix through ATP synthase, a process that couples the proton movement to the production of ATP. This is the primary mechanism of energy production in most cells.

Uncoupled mitochondria, found in brown adipose tissue (BAT), use a different mechanism. Instead of producing ATP, the proton gradient is dissipated through uncoupling protein 1 (UCP1), bypassing ATP synthase. This uncoupling process generates heat instead of ATP. This adaptation is vital for thermoregulation, especially in cold environments, as it allows organisms to produce heat rapidly and maintain their body temperature without relying on physical activity or shivering.

The presence of UCP1 in BAT makes it thermogenic, enabling efficient heat production, particularly in newborns and hibernating animals that rely on non-shivering thermogenesis to survive in cold conditions.

Question 33

Explain the concept of regional heterothermy and how countercurrent heat exchange helps animals like sled dogs and reindeer conserve heat.

Answer 33

Regional heterothermy is a phenomenon where different parts of an animal’s body maintain different temperatures. For example, in animals adapted to cold climates, such as sled dogs and reindeer, the core body temperature may be around 30–35°C, while the extremities, like feet or legs, can be close to 0°C. This adaptation minimizes heat loss from the extremities while preserving warmth in the vital core.

Countercurrent heat exchange is the mechanism that facilitates this process. In the limbs of these animals, arteries carrying warm blood from the core run adjacent to veins returning cooler blood from the extremities. As blood flows through the arteries, heat is transferred to the veins, warming the returning blood and reducing heat loss to the external environment. This ensures that by the time the blood returns to the body core, it has retained most of its heat, while the extremities remain cold and lose minimal heat to the environment. This mechanism is particularly beneficial for animals in cold climates to conserve energy and maintain their internal body temperature.