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Life Lines
The Science Podcast from The American Physiological Society
Questions and Answers
From Episode 3
Physiology of the Season
The American Physiological Society
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Question Sheet
Physiology of the Season
1) Name 3 physiological adaptations that reindeer have which enable them to survive
frigid conditions during a long period of time during the winter and explain how the
adaptations work.
2) “Rudolf the red-nosed reindeer” according to the song, was said to have a red and
shiny nose.” Do reindeer have red noses?
3) Reindeer stand on ice and snow much of the time, which causes their limbs to be
colder due to the ambient temperature which is conductive. What is a mechanism that
helps to prevent membranes in their limbs from freezing?
4) Reindeer may travel large distances with widely fluctuating temperatures. In traveling
to warmer temperatures, what limits their ability to get rid of excess heat and could
impede their function?
5) If temperatures keep getting hotter, reindeer respond by “blowing off” as much heat
as possible by panting. How does panting, which is a physiological adaptation, help to
get rid of heat and keep animals like reindeer, cool?
6) In addition to removing excess heat, what is another consequence of panting that can
be a problem for the animal?
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7) What are examples of adaptations that humans have to help them to deal with the
cold? Think about Santa’s physical appearance living in the North Pole, being exposed
to the elements, doing work and probably eating well.
8) What are behavioral adaptations that humans use to minimize heat loss?
9) Adaptations help in dealing with the cold, but they don’t mean that one is not getting
cold. What physiological adaptation might Santa’s red rosy cheeks indicate?
10) In thinking about ‘”Santa” who lives in the North Pole, what are some behavioral
adjustments that people who are well-adapted for living in a cold climate can do when
they have to go to a warm climate and need to cool off?
11) Give two examples of physiological adaptations to a warm environment and explain
how they cool the body.
12) How do humid conditions affect the ability to regulate body temperature?
13) During hot temperatures, how can one stay cool and prevent dehydration?
14) What happens if you get severely dehydrated?
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15) Sweating is a primary mechanism that humans use to cool down in the heat. When
you start getting low on water, name a hormone that the body releases which tells you
that you are getting thirsty and explain one way that it helps you to conserve water.
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Physiology of the Season
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Question and Answer Sheet
Physiology of the Season
1) Name 3 physiological adaptations that reindeer have which enable them to survive
frigid conditions during a long period of time during the winter and explain how the
adaptations work.
Answer: Reindeer have:
1) a thick subcutaneous fat layer underneath the skin that may be as much as 2
inches thick. This thick store of fat insulates the reindeer from the outside cold
and helps to keep the core body temperature warm.
2) a thick hair coat which provides substantial insulation from the cold and helps
conserve body heat. The insulating ability of the thick hair coat is improved by
their hollow-fibered hair which traps air within the hair follicle, as well as within
the under-fur.
3) a countercurrent mechanism for heat exchange which reduces the flow of cold
blood from extremities that are exposed to warm blood coming from their core.
This allows them to conserve the heat in blood by decreasing the rate at which
the cold blood returning from the limb draws heat from the incoming blood.
These 3 mechanisms all act to decrease heat loss from the reindeer.
Additionally, the fat also serves as an energy reserve. Reindeer don’t eat as
much in the winter and their metabolic rate is less.
Teacher note: It may be interesting to note sex differences with regard to body fat
reserve. After mating season, male reindeer go into winter in relatively poor
condition with approximately 5% body fat at a time when they have to deal with 45°F temperatures, which can be more challenging for male compared to female
reindeer.
2) “Rudolf the red-nosed reindeer” according to the song, was said to have a red and
shiny nose.” Do reindeer have red noses?
Answer: Reindeer are covered in fur except for their hoofs and eyes. They have
furry noses that are usually the white and grey colors of their snout. Fur provides
good insulation which is important in a cold environment, since anything moist
and exposed is likely to freeze unless there is very good blood flow to the
exposed tissue. Note that there would be a high metabolic cost to maintain the
blood flow under the frigid conditions.
3) Reindeer stand on ice and snow much of the time, which causes their limbs to be
colder due to the ambient temperature which is conductive. What is a mechanism that
helps to prevent membranes in their limbs from freezing?
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Answer: Fatty acids in membranes in reindeer limbs become more and more
unsaturated closer to the hoofs. The change in the composition of the
membranes prevents membranes from freezing. Additionally, this prevents
reindeer from feeling the cold as much.
4) Reindeer may travel large distances with widely fluctuating temperatures. In traveling
to warmer temperatures, what limits their ability to get rid of excess heat and could
impede their function?
Answer: It becomes more difficult for reindeer to function at higher temperatures
and exercise in warmer environments causes the body to warm up even faster.
Insulation that enables them to adapt to temperatures such as -45°F limits their
ability to get rid of excess heat when it becomes considerably warmer. If
reindeer have already developed the thick winter coat and thick fat pads, it is
difficult for them to keep cool enough for their muscles to keep functioning.
Although the countercurrent mechanism which allows them to conserve heat in a
cold climate can be regulated to allow them to dump heat at the body surface,
the amount of insulation that they have at the time is still going to limit the ability
to get rid of excess heat.
5) If temperatures keep getting hotter, reindeer respond by “blowing off” as much heat
as possible by panting. How does panting, which is a physiological adaptation, help to
get rid of heat and keep animals like reindeer, cool?
Answer: Panting allows heat to be lost through ventilation. The wet (moist)
surfaces of the mouth, palate and tongue are lined with water. Panting allows the
blood that is flowing under these surfaces to release heat to the surface and to
cause evaporation, a cooling process. Surface areas that are wet or moist
remove the heat and cool the blood. Because there is a good level of blood
flowing to this area, it can be used to remove a lot of heat from the animal. It is
important to have as large a surface area as possible for this loss of heat. When
animals pant, they open their mouths as much as possible and the tongue comes
out and also maximizes the surface area that allows for evaporation and removal
of heat from the blood flowing in the tongue. Parts of the animal that are not
sweating or moist, or that don’t have much blood flow, will gain or generate heat.
Sweating is not very effective for losing heat in animals that are covered in fur,
such as reindeer.
6) In addition to removing excess heat, what is another consequence of panting that can
be a problem for the animal?
Answer: Panting also causes evaporation of a lot of moisture (loss of water) from
the body. If animals are exposed to higher temperatures, they will need more
water to replace the increase in water lost through panting.
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7) What are examples of adaptations that humans have to help them to deal with the
cold? Think about Santa’s physical appearance living in the North Pole, being exposed
to the elements, doing work and probably eating well.
Answer: Santa is a large man with a large amount of subcutaneous fat that
insulates his internal organs and decreases heat loss to the environment. Heat
loss also has to do with a relationship called the surface area to body mass ratio.
A large body has a smaller surface area to body mass ratio than a small body.
The smaller body surface to body mass ratio favors a slower loss of heat to the
environment and is an advantage for living in the cold. Babies and small animals
like rodents have a large surface area to body mass ratio which causes a more
rapid loss of heat to the environment. The surface area to body mass ratio is a
critical determinant for heat loss prevention.
8) What are behavioral adaptations that humans use to minimize heat loss?
Answer: Humans can wear warm clothing. Santa wears a warm outfit including a
hat, gloves, and boots. Behavioral adaptations like a beard which protects the
face and cheeks also helps to minimize heat loss. Eating provides energy
needed for the demands of living in the cold and is another adaptation. When
you are cold, your metabolic rate increases. Expect people in a cold environment
to have a greater food intake because they are using more energy to stay warm.
9) Adaptations help in dealing with the cold, but they don’t mean that one is not getting
cold. What physiological adaptation might Santa’s red rosy cheeks indicate?
Answer: The redness of the cheeks indicates a distribution of blood to the cheeks
when this region of the face becomes cold. This is an example of a physiological
response to the cold, which is an adaptation to help keep the face warm. Unlike a
behavioral adaptation that occurs by a conscious behavior, this physiological
response is an adaptation that occurs unconsciously and is an “automatic
response.” In the cold, blood is normally shunted to the core of the body.
However, the body can redistribute some blood flow to the surface of areas of the
skin such as the cheeks by causing dilation of certain blood vessels. This
mechanism helps to transfer heat from the body to protect the skin from getting
too cold and to avoid frostbite.
Teacher note: In animals or humans that are kept in the cold, shivering (which
increases metabolic activity or rate) and vasoconstriction (which decreases blood
flow to certain regions) are other examples of physiological responses to the
cold. It is important to note that the physiological and behavioral adaptations are
all related to one another and don’t occur separately. Instead, they occur in
conjunction with one another to support the overall functioning of the body.
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10) In thinking about ‘”Santa” who lives in the North Pole, what are some behavioral
adjustments that people who are well-adapted for living in a cold climate can do when
they have to go to a warm climate and need to cool off?
Answer: People can remove warm clothes. This is a behavioral adjustment that
increases the amount of our body surface area that is exposed to a cooler
temperature. Santa’s layer of fat limits his heat loss and makes him poorly
adapted for migration to a warm climate. Santa could open his coat, take off his
gloves and hat and remove his warm boots. The hands, feet and head have a
large surface area that can be exposed to the air to help him cool off. Exposure
of these areas of the skin helps cool the blood flowing through your hands and
feet as it circulates to your core.
11) Give two examples of physiological adaptations to a warm environment and explain
how they cool the body.
Answer: Heat exposure leads to an increase in body temperature which acts to
dilate blood vessels and shunt blood to the skin surface to dissipate the extra
body heat by transferring it to the environment. This “vasodilation” is a
physiological adaptation mediated by the autonomic nervous system (which you
don’t have voluntary control over) that dissipates extra body heat. Blood is
shunted from internal organs to the skin surface which transfers heat through the
skin to the environment. The hands and feet are good for this because they have
a high surface area for dissipating the heat. Sweating is a physiological
adaptation that puts a “water” layer on the skin surface which evaporates and
cools the skin, allowing heat to dissipate from the body. When water evaporates,
it takes energy in the form of heat away from the body. In a hot environment it is
important for the skin to “breathe.” Sweat that is stuck between the skin and
fabric is not as effective in dissipating heat. Clothing that wicks moisture away
from the skin surface helps the cooling process.
Teacher note: Water is a good conductor of both heat and cold. In some conditions,
when the skin is wet, heat energy can be transferred from the environment to the
body, or cold can be transferred to the body.
12) How do humid conditions affect the ability to regulate body temperature?
Answer: The humidity in the air affects the rate of evaporation. With a high humidity,
the rate of evaporation is less and sweating is not as effective in cooling the
body.
13) During hot temperatures, how can one stay cool and prevent dehydration?
Answer: It is important to drink more fluids to maintain the hydration level and
prevent dehydration. Drinking water frequently reduces the risk for heat stroke
and dehydration. Since the body also loses electrolytes in hot temperatures, it is
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important that minerals and salts are also replaced in addition to water. Drinking
water with some electrolytes is good because you also lose salt in the sweat.
People in many climates, especially if exercising rigorously, may need to think
about drinking water or some sport drinks that replenish electrolytes.
14) What happens if you get severely dehydrated?
Answer: Levels of dehydration seen in heat stroke can be 10-15%. This can cause
the body to shut down because of the loss of water and a number of electrolytes
necessary for cells and organs to function. Severe dehydration can also cause
the blood to thicken or become more viscous which would make it more difficult
for the heart to pump the blood to the body tissues and organs.
Teacher note: Dehydration has many severe consequences and people who
exercise can become chronically dehydrated if they don’t consume sufficient
liquids. Behavioral adaptations are very important because the physiological
mechanisms occur “automatically” and may become fatigued without sufficient
support. This happens with heat stroke or with people who die from
hyperthermia. Your body can adjust for some time, but it requires a significant
amount of energy and that some other aspect of your functioning be shut off, at
least partially and temporarily, to accommodate for the regulation of your core
temperature. It is important to use the behavioral mechanisms that you have
available in order to put less stress on your body for it to maintain temperature in
either the heat or cold. Behavioral adaptations are more energetically efficient
than physiological adaptations and provide an evolutionary advantage. For
example, exposing the hands and feet and head to the environment by removing
clothes can help dissipate heat to the environment and acts together with the
physiological adjustments.
15) Sweating is a primary mechanism that humans use to cool down in the heat. When
you start getting low on water, name a hormone that the body releases which tells you
that you are getting thirsty and explain one way that it helps you to conserve water.
Answer: Antidiuretic hormone (ADH) causes thirst and also prevents you from
increasing your urine volume. ADH increases salt and water reabsorption and
decreases fluid loss through the kidney. If you are dehydrated enough to
stimulate this mechanism, you urinate less after you increase your drinking
behavior.
Teacher note: The body regulates many different variables such as temperature,
electrolytes, and plasma or blood volume and maintains them in a very narrow
range that we refer to as a set point.