*E1 Human Physiology - Regulation of body temperature Flashcards
Heat gain / Heat loss
Heat gain
- Respiration of body cells
- Radiation from the sun
Heat loss
- Evaporation of sweat
- Conduction, convection and radiation
Epidermis
Outermost layer (dead, cornified cells)
- Protect the inner structures from mechanical damage and invasion by pathogens
- waterproof, reduces water loss by evaporation
Middle layer
- When the cells in the middle layer are pushed up the skin surface, they become flattened and cornified by filling with keratin. These cells become dead cells in the outermost layer
Innermost layer (actively dividing cells)
- Dark pigment is present to protect the body by absorbing harmful ultraviolet radiation in sunlight
- Produces vitamin D under sunlight, helps absorption of calcium
- Newly produced cells replace those in outermost layer
Dermis
Sebaceous glands
- Produces oily sebum, makes hairs and skin waterproof to reduce excessive heat loss / makes the hair and skin supple to reduce breakage / acts as an antiseptic to kill bacteria and fungi
Sweat gland
- Secretes sweat, evaporation of sweat remove heat from the body surface, cooling down the body
Erector muscle
- Cold: contracts to pull the hair upright, increases thickness of air among hairs to reduce heat loss by conduction
- Hot: relaxes to lie the hair flat to reduce air trapped among the hairs to promote heat loss by conduction
Blood vessels, capillaries
- Vasoconstriction and vasodilation of blood vessels regulate the amount of blood flows to the skin surface, amount of heat loss can be controlled
Skin receptors
- Detect stimuli
Subcutaneous fat
- Good insulating layer to reduce heat loss
- Fat reserve
Mechanisms of regulations of body temperature
Arterioles
Cold:
- Vasoconstriction of arterioles in the skin occurs, reduces blood flow to the skin surface, reducing skin temperature. Less heat is lost from the blood to the surrounding through conduction, convection and radiation
- Most blood is diverted to flow through the shunt vessels to the venules
Hot:
- Vasodilation of arterioles in the skin occurs, this increases blood flow to the skin surface, increasing the skin temperature. More heat is lost from the blood to the surroundings through conduction, convection and radiation
Sweat gland
Cold:
- Sweating decreases, reduces heat loss from the body to the surrounding through evaporation of sweat
Hot:
- Sweating increases. Heat loss from the body increases through evaporation of heat, which absorbs the heat from the body surface
Erector muscles
Cold:
- Contraction of erector muscles pulls the hairs upright, which traps a thick layer of air above the skin surface to reduce heat loss by conduction
- For human, the hairs are too short, the air layer trapped is too thin to reserve heat effectively
Hot:
- Relaxation of erector muscles makes the hairs lying flat, traps a thinner layer of air above the skin surface to enhance heat loss from the skin to the surrounding
Shivering
Cold:
- Involuntary contraction of skeletal muscles causes the respiration rate of muscle increases, produces more heat to increase body temperature
Hot:
- No shivering
Subcutaneous fat (long-term)
Cold:
- Subcutaneous fat becomes thicker, which is a good insulator of heat
Hot:
- Subcutaneous fat becomes thinner, which reduces the insulating effect of the skin
How breathing quickly help dogs lose heat effectively
- Dogs breathe in cooler air into the lungs, which lowers the temperature of the blood flowing through the lungs
- Evaporation of water from the water film covering the inner surface of air sacs brings heat away from the lungs
- The blood capillaries of the air sacs warm the exhaled air, which carries heat away from the body
Hormonal control of body temperature
Cold:
- Secretion of thyroxine by thyroid glands increases. Thyroxine increases metabolic rate of body cells, more heat is generated to raise body temperature
Hot:
- Secretion of thyroxine by thyroid glands decreases. This decreases metabolic rate of body cells, less heat is produced
Voluntary behavioural methods to control heat loss
Cold:
- Put on clothes to trap more air to reduce heat loss from the body by conduction
- Curl the body to reduce surface area exposing to air
- Turn on heaters to gain heat by convection and radiation
- Do more exercise to generate heat in body
- Consumption of hot drinks provides heating effect
- Taking a cold shower
Effective: large temperature gradient between shower water and skin, heat is lost to the water from the skin by conduction
Not effective: causes vasoconstriction of arteriole, less blood and heat is brought to the skin surface
Resting after exercising
- Decreases rate of metabolism, reducing heat generation in body
Staying in air-conditioned room
- Large temperature gradient keeps the body cool by enhancing heat dissipation from the skin
Hot:
- Turn on air conditioners to establish steeper temperature gradient between skin and external environment, promoting heat loss by conduction, convection and radiation
- Go to shady places to reduce direct exposure to sunlight, decreases heat gain by radiation of sunlight
Putting paint all over the body
- The paint blocks the sweat pores so that sweat cannot escape through the sweat pore
- Heat loss through evaporation of sweat is reduced greatly
- When the rate of heat gain is faster than that of heat loss, this results in great increase of body temperature to a lethal level and lead to the breakdown of normal metabolism
Thermoregulation
Cold:
- Thermoreceptors in the hypothalamus detect the decrease in body temperature. Heat gain centre in the hypothalamus is stimulated to send out more nerve impulses to (receptor) + physiological response.
Hot:
- Thermoreceptors in the hypothalamus detect the increase in body temperature. Heat loss centre in the hypothalamus is stimulated to send out more nerve impulses to (receptor) + physiological response.
Why a slightly raised body temperature is beneficial in fighting a bacterial infection?
- Enzymatic reactions involved in the immune response proceed faster at a slightly raised body temperature.
- Higher temperature interfere with bacterial multiplication
Rubbing body with alcohol when having a fever
- Alcohol evaporates quickly, bringing away the heat from the body surface to lower the body temperature
Why dizziness occurs when overheating
- Prolonged sweating leads to excessive water loss from the body
- Blood volume decreases
- Inadequate blood flow to the brain to supply enough oxygen
-Vasodilation of arteriole increases blood flow to skin surface to increase heat loss to the surroundings by conduction, convection and radiation
- Inadequate blood flow to the brain to supply enough oxygen
[Dizziness = inadequate supply of oxygen / blood / nutrients]
Why heat loss is mainly affected through sweating when air temperature is higher than body temperature?
- Heat from the body could not be lost to the environment by conduction, convection and radiation
- Heat would be lost through evaporation of sweat which absorbs heat from the body surface
Why would it be more dangerous to carry our vigorous exercise when the relative humidity is high?
- Sweat could not evaporate efficiently, less heat was lost from the body through sweating
- Undergoing vigorous exercise would generate a large amount of heat
- When the rate of heat fain is faster than the rate of heat loss, the body temperature will rise steadily, leading to the breakdown of normal metabolism
Why can staying in shady place help lower the body temperature?
- The skin is shielded from direct sunlight in a shady place, reducing heat gain by radiation by the body, preventing it from overheating
- The temperature of shady place is lower than exposed area, increasing heat loss by radiation and convection to the environment
