Answers to Chapter 29 DYUC

Do You Understand Concept 29.2?

A regulatory system you encounter often is the thermostatically controlled heat and air conditioning system that keeps a building’s temperature constant in changing external conditions. Describe such a system in terms of the regulating system, the controlled system, the set points, feedback information, and effector commands.

Answer:
The temperature of a building is controlled by the actions of a heater and an air conditioner, which constitute the controlled system. The actions of the heater and air conditioner are turned on or off by effector commands from a regulatory system, or thermostat. The setting on the thermostat is the set point, and the thermostat is sensitive to the surrounding air temperature, which provides feedback information. When the set point is different from the feedback information, error signals are generated that are transduced into effector commands controlling the heater and air conditioner.

Do You Understand Concept 29.3?

What are some cellular processes or events that would lead to the survival of cells being limited to an approximately 40^oC range of temperatures?

Answer:

Above this temperature proteins begin to denature and lose their function. Below this range ice crystals can form in cells, leading to cell death.

Explain how a physiological process can be disrupted by changes in its temperature when its component biochemical reactions have different Q₁₀’s.

Answer:

A physiological process involves many biochemical reactions that are interlinked, with the products of one being the reactants of another. If the rates of these reactions change differentially with a change in temperature, the integration of the interlinked reactions will be disturbed.

Why does MR of a mammal increase as T_adecreases, whereas MR of a reptile decreases as T_adecreases, in the range of T_a’s below 25^oC in the example in the figure?

Answer:

In T_a’s below 25^oC, a mammal’s MR will rise in response to its need to increase metabolic heat production to maintain its internal temperature. The reptile cannot increase its MR to compensate for increasing heat loss as T_a falls, therefore its tissues will cool and its MR will fall because of the Q₁₀’s of its biochemical and physiological processes.

Do You Understand Concept 29.4?

Compare the two foxes in Figure 29.9 and explain how the differences you observe influence each element of the heat balance equation for these two species.

Answer:

The desert fox has long limbs, short fur, large ears, and a thin, long body to allow heat to escape its body, whereas the arctic fox has long fur, small ears, short limbs, and a compact body. In the arctic fox, the heavier insulation (fur) and smaller surface area (body shape, limb length, ear size) decrease heat loss from radiation, convection, and conduction.

Many newborn mammals have brown fat even if brown fat is not seen in adults of that species. Why is brown fat adaptive for newborns?

Answer:

Brown fat allows for non-shivering thermogenesis, an efficient and stable source of metabolic heat that does not produce ATP and therefore does not limit the metabolic rate due to the buildup of ATP. Its presence enhances a newborn's chances of surviving cold exposure.

For both hot and cold stress, explain how behavioral adaptations can alter heat exchange through all of the components of the heat budget equation.

Answer:

When heat stressed, behavior can be used by an animal to find a cooler environment that will decrease absorption of thermal energy and facilitate convective and conductive heat loss. Seeking and ingesting water can support evaporative heat loss; immersion in water can dissipate heat through conductive and convective heat loss to the water. Getting into or creating a convective air stream can increase heat loss by convection. In the cold, behavior can be used to increase insulation (piloerection, huddling, decreasing surface area). Basking can increase radiation absorbed. Activity can increase metabolic heat production.

If sweating and panting are such costly avenues of cooling (due to water loss and metabolic energy expenditure), why haven’t evolutionary mechanisms eliminated them as regulatory mechanisms?

Answer:
Evaporative heat loss is extremely effective as an emergency means of lowering body temperature because of the very high amount of heat that is required to take water from the liquid to the gaseous phase (heat of vaporization).

Do You Understand Concept 29.5?

Draw a diagram of the mammalian thermostat that includes the effectors, the set points, and the negative feedback.

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Explain at least four sources of feedforward information for the mammalian thermostat that can either keep body temperature constant in spite of changes in the environment, or can cause body temperature to change.

Answer:

Skin temperature is feedforward information that can prevent rises or falls in body temperature as the animal moves between different ambient temperatures.

The onset of activity is feedforward information that can increase heat loss (sweating or panting) in advance of a rise in body temperature.

Circadian rhythms and the onset of sleep is feedforward information that changes the set points of the thermoregulatory system to achieve increases or decreases in body temperature.