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What is the constant temperature of the body?

36.8 degrees


What is thermoregulation?

Maintaining the balance between heat production and heat loss


Why is thermoregulation important?

Because the chemical reactions between cells are very heat sensitive


Why does excess heat need to be removed?

In order to prevent the body temperature from rising
Other wise it can
- cause nerve malfunction
- changes in the structure of proteins
- death


Thermoregulation feedback...

Negative feedback
- Stimulus: change in body temperature
- Receptors: thermoreceptors
- Modulator: hypothalamus
- Effectors: blood vessels and sweat glands
- Response: vasodilation/vasoconstriction or perspiration rate
- Feedback: change in body temperature


What is metabolic rate?

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


Factors that effect metabolic rate

Factors such as exercise (greatest effect), stress and body temperature affect the metabolic rate


Exercise (metabolic rate)

- Muscular activity can increase metabolic rate by up to 40 times
- Very large quantities of heat are released


Stress (metabolic rate)

- Sympathetic nerves release nor adrenaline from nerve endings
- Increases metabolic activity of cells


Body temperature (metabolic rate)

- For each 1⁰C rise in body temperature, the rate of biochemical reactions increases by 10%
- When an individual is suffering from a high fever, body temperature may double


Peripheral thermoreceptors

- Located in the skin and some membranes
- Provide information about the external environment
o Cold receptors – stimulated by environmental temperatures lower than usual
o Heat receptors – detect temperatures higher than usual
- Both feed information back to the hypothalamus


Central thermoreceptors (location)

Located in the hypothalamus, spinal cord and abdominal organs


Ways heat can be lost from the skin:

- Conduction
- Convection
- Radiation
- Evaporation



- Occurs from direct contact with heat source
- EG. Standing on hot sand with bare feet



- Occurs when hot or cold air passes over a body
- EG. When you get goose bumps when you get cold, there is a layer of air trapped between your hairs and your skin, this air becomes hot and passes over the skin.



- The transformation of water from liquid to gas
- Evaporation of sweat results in heat loss



- There is no direct contact with the heat source


Diameter of blood vessels

- Controlled by the autonomic nerves
- Can decrease or increase the flow of blood near the surface of the skin
- Can therefore control the amount of heat lost
- These adjustments are automatic



- The active secretion of fluid from the sweat glands
- Periodic contraction of cells surrounding the sweat glands
- Pump sweat to the surface
- Stimulated by the sympathetic nerves
- Is water containing NaCl, small amounts of urea, lactic acid and potassium ions
- When sweat evaporates it has a cooling effect


Where does water also evaporate from?

Water also evaporates from the lungs and respiratory passages


What happens when environmental temperatures fall?

1. Cold receptors in the skin are stimulated to send messages to the hypothalamus
2. The hypothalamus sends out impulses with the aim of reducing heat loss or increasing heat production


5 responses that prevent body temperature from falling

Secretion of hormones
Increased production of thyroxine
Behavioral responses


Vasoconstriction (in the skin) to prevent body temperature from falling

- Impulses from the hypothalamus stimulate sympathetic nerves that cause blood vessels in the skin to constrict
- Decreasing the flow of warm blood to the skin
- Decreasing the transfer of hear from the internal organs to the skin
- Skin becomes cooler, as less heat can escape from the body surface


Secretion of hormones to prevent body temperature from falling

- Initiated by the hypothalamus
- Stimulation of adrenal medulla by the sympathetic nerves
- Results in the secretion of adrenaline and noradrenalin
- Increase in cellular metabolism which leads to an increase in heat production


Shivering to prevent body temperature from falling

- The hypothalamus sends nerve impulses to parts of the brain to increase skeletal muscle tone
- Leads to oscillating, rhythmic muscle tremors occurring at a rate of around 10-20 per second
- This increases body heat production


Increased production of thyroxine to prevent body temperature from falling

- Hypothalamus causes the anterior lobe of the pituitary to secrete TSH, causing the thyroid gland to secrete thyroxine
- This increases the metabolic rate, causing an increase in body temperature
- Has a slower, but longer lasting effect. Occurs between warm summer months and cool winter ones


Behavioral responses to prevent body temperature from falling

A person will become consciously aware of cold conditions and may:
- Put on an extra jumper
- Shelter from cold wind
- If they are cold in bed, they may curl up into a ball


Ways to prevent body temperature from rising

- Vasodilation of the blood vessels in the skin
- Sweating
- Decrease in metabolic rate
- Behavioural responses


Vasodilation of blood vessels in the skin (preventing body temperature from rising)

- Increase blood flow to the skin
- Skin becomes a reddish colour
- Surface temperatures rise and therefore there is greater heat loss though radiation and convection


Sweating (preventing body temperature from rising)

- Increases heat loss from the body
- More effective in dry air, sweating cannot evaporate when it is humid