8.1.3 Thermoregulatory Strategies in Man

Thermoregulatory center in human body is located in the hypothalamus which acts as a thermostat. It can detect the temperature of the blood that passes through it and if the temperature increases or decreases even slightly, the hypothalamus initiates corrective responses such as sweating or shivering.

Definition

Thermoregulatory Strategies in Man: Thermoregulatory center in human body is located in the hypothalamus which acts as a thermostat. It can detect the temperature of the blood that passes through it and if the temperature increases or decreases even slightly, the hypothalamus initiates corrective responses such as sweating or shivering.

Main Idea

• Thermoregulatory center is located in the hypothalamus.
• Hypothalamus acts as a thermostat.
• It detects temperature of the blood.
• If temperature increases or decreases slightly, hypothalamus initiates corrective responses.
• Corrective responses include sweating or shivering.
• Temperature receptors in the skin inform the hypothalamus.
• They also stimulate the higher, voluntary centers of the brain.
• We feel changing our clothing or turning the heating up or down.
• Behavioral response corrects the situation without physiological response.

Core Concept

• Thermoregulatory center = hypothalamus
• Hypothalamus = acts as thermostat
• Detects = temperature of blood
• Corrective responses = sweating or shivering
• Skin receptors = inform hypothalamus
• Behavioral response = changing clothing or heating
• Physiological responses to heat = vasodilation, sweating
• Physiological responses to cold = shivering, vasoconstriction, piloerection, increased metabolic rate

Detailed Explanation

Thermoregulatory Strategies in Man

• Thermoregulatory center in human body is located in the hypothalamus which acts as a thermostat.
• It can detect the temperature of the blood that passes through it and if the temperature increases or decreases even slightly, the hypothalamus initiates corrective responses such as sweating or shivering.
• When we encounter a particularly warm or cold environment, temperature receptors in the skin inform the hypothalamus.
• They also stimulate the higher, voluntary centers of the brain.
• This means that we feel changing our clothing or turning the heating up or down.
• Often, this behavioral response corrects the situation without the need for any physiological response.

Physiological Responses to Heat

• Vasodilation
• Sweating

Vasodilation

• One way to increase heat loss is to supply the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation.
• Arterioles have muscles in their walls that can relax or contract to allow more or less blood to flow through them.
• During vasodilation these muscles relax, causing the arterioles near the skin to dilate and allowing more blood to flow through capillaries.

Sweating

• Sweat is a salty solution made by sweat glands.
• Evaporation of sweat from the skin's surface leads to cooling.
• As the sweat evaporates, it absorbs heat from the body, thereby cooling the skin and helping to regulate internal body temperature.
• The efficiency of sweating depends on humidity.
• In dry air, humans can tolerate temperature of 65°C for several hours.
• In humid air, however, when the sweat cannot evaporate, temperatures of only 56°C cause overheating.

Physiological Responses to Cold

• Shivering
• Vasoconstriction
• Piloerection
• Increased metabolic rate

Shivering

• We shiver when muscles contract and relax rapidly.
• Shivering muscles give out four or five times as much heat as resting muscles.

Vasoconstriction

• One way to decrease heat loss is to supply the capillaries in the skin with a smaller volume of blood, minimizing the loss of heat to the environment via radiation.
• During vasoconstriction the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through capillaries.
• The blood is diverted through shunt vessels, which are further down in the skin and therefore do not lose heat to the environment.
• Vasoconstriction reduces heat loss from the blood as it flows through the skin.

Piloerection

• It means literally 'erection of hairs' and involves a reflex.
• In most mammals, piloerection makes the fur 'thicker', so that it traps more air to provide extra insulation.
• In humans, the erector pili muscles in the skin pull the tiny hairs upright, and succeed in creating goose bumps.

Increased Metabolic Rate

• The body secretes the hormone adrenaline in response to cold.
• This raises metabolic rate and therefore increases heat production.

Summary Table of Thermoregulatory Strategies

Intermediate Level

Thermoregulatory Strategies in Man

Physiological Responses to Heat

Physiological Responses to Cold

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Thermoregulatory center is in the hypothalamus.
• 2. Hypothalamus acts as a thermostat.
• 3. It detects blood temperature.
• 4. It initiates corrective responses.
• 5. Corrective responses include sweating or shivering.
• 6. Skin receptors inform hypothalamus.
• 7. Behavioral responses include changing clothing.
• 8. Physiological responses to heat: vasodilation and sweating.
• 9. Vasodilation increases heat loss.
• 10. Sweating cools the body.
• 11. Sweating efficiency depends on humidity.
• 12. Physiological responses to cold: shivering, vasoconstriction, piloerection, increased metabolic rate.
• 13. Shivering increases heat production.
• 14. Vasoconstriction decreases heat loss.
• 15. Piloerection traps air for insulation.
• 16. Increased metabolic rate increases heat production.
• 17. Adrenaline raises metabolic rate.
• 18. In dry air, humans tolerate 65°C.
• 19. In humid air, 56°C causes overheating.
• 20. Behavioral responses can correct situation without physiological response.

Remember

• - Thermoregulatory center = hypothalamus
• - Hypothalamus = acts as thermostat
• - Detects = temperature of blood
• - Corrective responses = sweating or shivering
• - Skin receptors = inform hypothalamus
• - Behavioral response = changing clothing or heating
• - Physiological responses to heat = vasodilation, sweating
• - Physiological responses to cold = shivering, vasoconstriction, piloerection, increased metabolic rate

Common Mistakes

• 1. Thinking the hypothalamus is not involved — It is the control centre.
• 2. Confusing vasodilation and vasoconstriction — Vasodilation = widening; vasoconstriction = narrowing.
• 3. Mixing up the responses to heat and cold — Heat: vasodilation, sweating; cold: shivering, vasoconstriction.
• 4. Forgetting the role of skin receptors — They inform the hypothalamus.
• 5. Mixing up piloerection and shivering — Piloerection = hairs stand up; shivering = muscles contract.
• 6. Forgetting the role of adrenaline — Raises metabolic rate.
• 7. Believing sweating is effective in humid air — Sweating is less effective in humid air.
• 8. Mixing up the temperature tolerances — Dry air: 65°C; humid air: 56°C.
• 9. Forgetting behavioral responses — Changing clothing, seeking shade.
• 10. Mixing up the effects — Vasodilation increases heat loss; vasoconstriction decreases heat loss.

Quick Revision

Thermoregulatory center in human body is located in the hypothalamus which acts as a thermostat. It can detect the temperature of the blood that passes through it and if the temperature increases or decreases even slightly, the hypothalamus initiates corrective responses such as sweating or shivering. When we encounter a particularly warm or cold environment, temperature receptors in the skin inform the hypothalamus. They also stimulate the higher, voluntary centers of the brain. This means that we feel changing our clothing or turning the heating up or down. Often, this behavioral response corrects the situation without the need for any physiological response. There are two main physiological responses when hypothalamus detects an increase in blood temperature: vasodilation and sweating. There are four main physiological responses when hypothalamus detects a drop in blood temperature: shivering, vasoconstriction, piloerection, and increased metabolic rate.

60-Second Revision

• Thermoregulatory center = hypothalamus
• Hypothalamus = acts as thermostat
• Detects = temperature of blood
• Corrective responses = sweating or shivering
• Skin receptors = inform hypothalamus
• Behavioral response = changing clothing or heating
• Physiological responses to heat = vasodilation, sweating
• Physiological responses to cold = shivering, vasoconstriction, piloerection, increased metabolic rate
• Warning: Vasodilation increases heat loss; vasoconstriction decreases heat loss

NEXT TOPIC

• Chapter:
• 8. Thermoregulation and Homeostasis

• Topic:
• 8.2 HOMEOSTASIS

Source: