Chapter 5.3 Thermoregulation ✔

Question 1

Define thermoregulation

Answer 1

The regulation of body temperature; the balance of heat gain and heat loss in order to maintain a constant internal body temperature independent of the environment temperature

Question 2

Define metabolic rate

Answer 2

The rate at which energy is released to the body by the breakdown of food

Question 3

What can affect the metabolic rate?

Answer 3

-Exercise (has the greatest effect)
-Stress
-Body temperature

Question 4

Define thermoreceptor

Answer 4

A temperature receptor; located in the skin or hypothalamus

Question 5

Define peripheral thermoreceptors

Answer 5

A thermoreceptor in the skin and in some mucous membranes

Question 6

Define central thermoreceptors

Answer 6

A thermoreceptor located in the hypothalamus

Question 7

What are the two types of thermoreceptors?

Answer 7

Cold and heat receptors

Question 8

Define cold receptor

Answer 8

A receptor that is stimulated by low temperature

Question 9

Define heat receptor

Answer 9

A receptor that is stimulated by high temperature

Question 10

What happens when cold receptors are stimulated?

Answer 10

The hypothalamus receives the information and initiates heat conservation and heat production mechanisms

Question 11

What happens when heat receptors are stimulated?

Answer 11

The hypothalamus receives the information and mechanisms operate to reduce heat production and increase heat loss

Question 12

What four ways does the body lose heat?

Answer 12

-Conduction
-Convection
-Radiation
-Evaporation

Question 13

Define conduction

Answer 13

The transfer of heat by direct contact between particles

Question 14

Define convection

Answer 14

The transfer of heat by the movement of a liquid or gas

Question 15

Define radiation

Answer 15

The transfer of heat by infrared radiation being emitted by objects

Question 16

Define evaporation

Answer 16

Process of a liquid forming a gas, which absorbs heat energy

Question 17

What controls the diameter of arterioles?

Answer 17

Autonomic nervous system or autonomic nerves

Question 18

Define vasodilation

Answer 18

An increase in the diameter of arterioles, increasing the flow of blood through them

Question 19

Define vasoconstriction

Answer 19

A decrease in the diameter of arterioles, restricting the flow of blood through them

Question 20

Define sweating

Answer 20

The active secretion of fluid by sweat glands.

Question 21

Define shivering

Answer 21

Oscillating, rhythmic muscle tremors that increase the body temperature

Question 22

How does the body respond when the environment temperature falls?

Answer 22

-The body can respond by making physiological changes (changes in body functioning) and behavioural changes

• Vasoconstriction:
  Impulses from the hypothalamus stimulate sympathetic nerves, causing arterioles in the skin to constrict. This decreases the flow of warm blood from internal organs to the skin, reducing heat transfer to the surface. The skin becomes cooler due to reduced warm blood flow. Less heat is lost from the body surface.
• Stimulation of the adrenal medulla:
  Another response from the hypothalamus is stimulating the adrenal medulla via sympathetic nerves. This causes the medulla to release adrenaline and noradrenaline into the blood, increasing cellular metabolism and heat production. This helps maintain body temperature during rapid heat loss.
• Shivering:
  A drop in body temperature prompts the hypothalamus to activate parts of the brain that cause shivering, which increases heat production within minutes. Shivering is mainly controlled by the hypothalamus but can be consciously suppressed by the cerebral cortex.
• Increase thyroxine production:
  The hypothalamus causes the pituitary gland to release TSH, stimulating the thyroid gland to release thyroxine. Higher thyroxine levels raise the metabolic rate and increase body temperature. This response is slower but longer lasting. Seasonal changes in metabolic rate are partly due to this.
• Behavioural changes:
  If we become aware of the cold, we may act to reduce heat loss—like putting on a jumper or sheltering from the wind. Curling up to reduce surface area also helps conserve heat.

Question 23

How does the body respond when the environment temperature rises?

Answer 23

-The body can respond by making physiological changes (changes in body functioning) and behavioural changes

-Vasodilation
Vasodilation of skin arterioles increases blood flow to the skin, making it redder and warmer. This raises surface temperature and increases heat loss through radiation and convection.

-Sweating
When temperatures exceed ~28°C, sweating helps cool the body. It’s most effective in dry environments where sweat can evaporate. In high humidity, sweat can’t evaporate properly, causing discomfort and reducing cooling. If temperatures rise above 37°C, the body gains heat from the environment, and evaporation of sweat becomes the only way to lose heat.

-Decreased thyroxine production
Over time, the body can reduce its metabolic rate to produce less heat. This occurs through decreased thyroxine secretion, particularly during summer when heat loss is limited.

-Behavioural responses
Behavioural responses like using fans or air conditioners, removing clothing, and reducing activity help prevent the body temperature from rising.

Question 24

What temperature should the body maintain homeostasis?

Answer 24

36.8°C

Question 25

Define heat stroke

Answer 25

The failure of a person's temperature-regulating mechanisms when exposed to excessive heat

Question 26

Define heat exhaustion

Answer 26

The collapse of a person after exposure to heat, during which their body's heat-regulating mechanisms continue to function normally

Question 27

Define hypothermia

Answer 27

Abnormally low body temperature; the temperature drops below the level required to maintain normal body functions

Question 28

Why is the skin important in regulating body temperature?

Answer 28

Because it controls heat loss or retention through vasodilation, vasoconstriction, sweating, and acts as a large surface for heat exchange and sensory detection.

Question 29

List five responses that the hypothalamus would trigger on a hot day. For each, classify them as responses from the nervous system or endocrine system.

Answer 29

-Vasodilation of skin arterioles System: Nervous system Effect: Increases blood flow to the skin, promoting heat loss through radiation and convection. -Sweating System: Nervous system Effect: Activates sweat glands to release sweat, which cools the body via evaporation. -Reduced thyroxine secretion System: Endocrine system Effect: Lowers metabolic rate to reduce internal heat production. -Reduced adrenaline and noradrenaline release System: Endocrine system (via sympathetic nervous stimulation of the adrenal medulla) Effect: Decreases metabolic rate and heat production. -Behavioural responses (e.g., seeking shade, removing clothing) System: Nervous system (involving conscious processing via the cerebral cortex) Effect: Helps limit further heat gain and promotes heat loss.

Question 30

List five responses that the hypothalamus would trigger on a cold day. For each, classify them as responses from the nervous system or endocrine system.

Answer 30

-Vasoconstriction of skin arterioles System: Nervous system Effect: Reduces blood flow to the skin, conserving body heat by minimizing heat loss. -Shivering System: Nervous system Effect: Involuntary muscle contractions generate heat to raise body temperature. -Increased thyroxine secretion System: Endocrine system Effect: Raises metabolic rate, increasing heat production. -Adrenaline and noradrenaline release System: Endocrine system (stimulated by the nervous system) Effect: Boosts cellular metabolism, generating additional heat. -Behavioural responses (e.g., putting on warm clothes, curling up) System: Nervous system (via conscious processing) Effect: Reduces heat loss and helps retain warmth.

Question 31

Which is more dangerous, heatstroke or heat exhaustion? Explain why.

Answer 31

-Heatstroke is more dangerous than heat exhaustion. -Heatstroke is a life-threatening condition where the body's thermoregulatory system fails, and core body temperature rises above 40°C. -It can lead to organ failure, brain damage, or death if not treated immediately. The skin may feel dry (sweating stops), and the person may become confused, unconscious, or have seizures. -Heat exhaustion, on the other hand, is less severe and results from excessive loss of water and salt through sweating. -It causes symptoms like dizziness, weakness, nausea, and heavy sweating, but core temperature is usually below 40°C, and the body can still regulate itself. With rest and hydration, recovery is typically quick.

Question 32

Heat flows from areas of high temperature to low temperature. How does the body maintain a temperature above that of the surrounding environment?

Answer 32

-The body maintains a higher internal temperature than the environment by actively producing and conserving heat. -Heat Production: The hypothalamus increases metabolic activity by stimulating the release of thyroxine (from the thyroid) and adrenaline/noradrenaline (from the adrenal medulla), which raise the metabolic rate and generate more internal heat. -Shivering, controlled by the hypothalamus, also increases heat production through involuntary muscle contractions. -Heat Conservation: To prevent heat loss, the hypothalamus triggers vasoconstriction of skin arterioles, reducing blood flow to the skin and minimizing heat transfer to the environment. -Behavioural Responses: The body also relies on conscious actions such as putting on warm clothing, seeking shelter, and reducing exposed surface area (e.g., curling up), which further conserve heat. These physiological and behavioural mechanisms together allow the body to maintain a stable core temperature (~37°C), even in cold environments

Question 33

Compare and contrast vasodilation and vasocontraction

Answer 33

Definition -Vasodilation: Widening of blood vessels -Vasocontraction: Narrowing of blood vessels Blood flow -Vasodilation: Increases blood flow to the skin -Vasoconstriction: Decreases blood flow to the skin Heat Regulation -Vasodilation: Promotes heat loss -Vasoconstriction: Conserves heat Skin appearance -Vasodilation: Skin may appear red and feel warm -Vasoconstriction: Skin may look pale and feel cold# Nervous system control -Vasodilation: Triggered by hypothalamus via nerves -Vasoconstriction: Triggered by hypothalamus via nerves Occurs when... -Vasodilation: Body is too hot -Vasoconstriction: Body is too cold

Question 34

Explain why sweating is more effective at cooling the body when the humidity is low.

Answer 34

-Sweating cools the body by releasing moisture onto the skin, which absorbs body heat as it evaporates. The key to this cooling process is evaporation. -When humidity is low, the air has less water vapor, so it can easily absorb the sweat from your skin. This allows sweat to evaporate quickly, taking heat with it and cooling the body efficiently. -When humidity is high, the air is already saturated with water vapor, so evaporation slows down or stops. As a result, sweat stays on the skin or drips off without removing much heat, making the cooling process far less effective.

Question 35

Other than sweating, what other modes of evaporation occur in the body?

Answer 35

Respiratory Evaporation: When you breathe, moisture from the respiratory tract evaporates into the exhaled air. This process contributes to heat loss, especially when body temperature rises above 37°C

Question 36

People who live in cold climates don't seem to feel the cold as much as visitors to the area. Explain why this happens.

Answer 36

Improved Heat Conservation (Effectors activated by the hypothalamus): -Vasoconstriction becomes more efficient: Blood vessels near the skin narrow to reduce heat loss from the body’s surface. -Increased insulation: Regular exposure to cold can lead to slightly increased subcutaneous fat, which helps trap body heat. Enhanced Heat Production: -Shivering thermogenesis: Cold-acclimated individuals often have more efficient or quicker shivering responses, generating heat through muscle activity. -Non-shivering thermogenesis: In some cases, increased activity of brown adipose tissue (brown fat) enhances metabolic heat production without shivering. Set Point Sensitivity: -The hypothalamus, which controls thermoregulation, may adjust its sensitivity. In cold-acclimated individuals, the body may tolerate a slightly lower core or skin temperature before activating strong cold responses, meaning they feel less discomfort in the cold. Behavioural Thermoregulation: -Long-term residents also learn better behavioural strategies to minimize heat loss, such as appropriate layering, movement patterns, and recognizing early signs of cold stress.