Thermoregulation

What is thermoregulation?

Involves the regulation of body temperature to keep the body’s core temperature within its tolerance limits.

What is the body temperature of humans?

Constant at about 36.8°C

Why is the body temperature of humans kept at a constant 36.8°C?

optimum for cellular respiration (cells function at stable manner)

Does the human body try and always keep a constant temperature?

Yes - heat gained by body must exactly equal heat lost from the body.

Variation does occur: stenuous activity, changes in external temperature, etc.

What macronutrients provide the human body heat energy?

• carboydrates

• proteins

• lipids

What is metabolic rate?

the rate at which energy is released by the breakdown of food

• affected by many factors (e.g. exercise, stress, body temperature)

What receptors detect changes in body temperature?

Thermoreceptors.

What are thermoreceptors located?

• peripheral thermoreceptors

  • detect temperature changes in the external enviroment and send information to the hypothalamus, located in the slin and some mucous membranes

• central thermoreceptors

  • detect temperature changes in the internal enviroment, located in the hypothalamus

• additional thermoreceptors at various internal locations

  • detect temperature changes in the internal enviroment, send infromation to the hypothalamus, located in the spinal cord, abdominal organs, etc.

What are the 2 types of thermoreceptors?

• Cold receptors

  • stimulated by a decrease in body temperature → hypothalamus receives infortmation and iniates heat conservation and heat production mechanisms

• Heat receptors

  • stimulared by an increase in body temperature → hypoythalamus recieves information and iniates mechanisms to reduce heat production and increase heat loss from the body

How does the skin assist in temperature regulation of the body?

• conduction: transfer of heat by direct contact between particles

• convection: trasnfer of heat by movement of a liquid or gas

• radiation: transfer of heat by infared raditation emitted by objects

• evaporation: process of liquid → gas, which absorbs heat

How do blood vessels assist in heat loss/gain?

• blood vessels located in the dermis of the skin carry heat to the skin from the core of the body

• autonomic nerves control diamter of arterioles

  • vasodilation: diamter increased, more blood transported to capillaries in the skin and the rate of heat loss increases

  • vasoconstriction: diamter decresed, less blood transported to capillaries in the skin and the rate of heat loss decreases

How does sweating assist heat loss?

• sweating occurs when large amounts of heat must be lost and skin vessels are at maximum dilation

• sweating: an active secretion of fluid by the sweat glands and periodic contraction of cells surrounding the ducts to pump the sweat to the surface of the skin

  • production and transportation of sweat to the surface of the skin stimulated by sympathetic nerves

• evaporation of sweat from the skin has a cooling effect

  • heat removed from the skin when the liquid sweat turns into vapour, resulting in the cooling of blood flowing throught the skin

What is sweat?

Water containing dissolbed substances, primarily sodium chlordie along with small amounts of urea, lactic acid and potassium ions.

How does shivering assist in heat gain?

• shivering is due to an increase in skeletal muscle tone, producing rhythmic muscle termors that occur at a rate of around 10 to 20 per second

• as for no work is being done, all energy produced by the muscles is released as heat

How does the body prevent temperature from falling?

Cold receptors in the skin send messages to the hypothalamus if the enviroment becomes colder.

Physiological changes and behavioural changes:

• impulses from hypothalamus stimulate sympathetic nerves → arterioles in the skin constrict (vasoconstriction → decreases flow of warm blood to skin from internal organs)

• hypothalamus stimulates adrenal medualla by sympathetic nerves → secretion of adrenaline and noradrenaline (increase cellular metabolism increasing heat production)

• hypothalamus sends stimulus to parts of the brain to cause shivering (increase heat production, conscious input from cerebral cortex can suppress urge to shiver)

• behavioural response: we become consciously aware of cold contions, pressuring us to move to warmer enviroments, wearing warmer clothes, etc., helping reduce heat loss

How does the body prevent body temperature from rising?

• vasodilation of skin arterioles → increase blood flow to skin (skin becomes reddish, surface temp. rises, greater heat loss through radiation and convection)

• sweating (enviroment termperatures above 28°C, most effective in dry air, greater than 37°C heat is gained from enviroment and evaportation of sweat is only avenue for heat loss)

What core body temperature is dangerous?

42°C is dangerous, death usually occurs if it rises above 45°C

How can high body temperatures occur?

• fever

• certain enviromental conditions (temperature, humidity)

• strenuous exercise

What is the best treatement for cooling the body?

Cold water submersion

What is heat exhastion?

Occurs as areult of extreme sweating and vasodilation to lose heat, reducing the volume of blood plasma and the vasodilation reduces resistance to blood flow, reducing blood pressure, and output of blood from heart decreases

• person may collapse

• body temperature is almost normal (not heat stroke)

When does hypothermia occur?

Death can occur at core temperatures below 32°C, but some people have been known to survive even lower temperatures,

If a persons core temperature falls below 33°C, the metabolic rate is slow that heat production is unable to replace the heat lost and the body temperature continues to fall.

What is heat stroke?

Body temperature rises and the regulatory mechanisms cease.

Occurs when the temperature and relative humidity are high, it is difficult for the body to lose heat by radiation or evaportation.

Can be very serious, even fatal, if brain cells affected.