Access Human Biology.
Temperature Regulation.
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Heat Production.
 Energy produced by cell metabolism is
in the form of heat.
 The most active organs create most
heat.
 Principle heat producing organs are:
- Skeletal Muscles.
- The Liver.
- Organs of Digestion.
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The Liver.
 High metabolic activity (very busy!).
 Heat produced as a bi-product.
 Metabolic rate thus heat are increased
after eating.
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Body Temperature.
 Normal body temperature - 36-37 C.
 Hypothermia: Dangerous lowering of body
temperature - <35 C.
 Pyrexia: High temperature - >37.1 C.
 Hyperpyrexia: Dangerously high
temperature - >41.1 C.
 Homeostasis means maintaining a balance
between heat production and heat loss.
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Skeletal Muscles.
 Contraction of skeletal muscle produces
heat.
 More strenuous the exercise - the more
heat produced.
 Shivering: Contraction of skeletal
muscle to produce heat when body
temperature is at risk of falling.
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Digestion.
 Digestive organs produce heat during
peristalsis.
 Chemical reactions during digestive
process also cause heat production.
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Heat Loss.
 Small amounts of heat are lost in:
- Expired air.
- Faeces.
- Urine.
 No control over this heat loss.
 Most body heat lost through the skin.
 Only heat loss through skin can be
regulated
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Heat Loss: Mechanisms.
 Evaporation: Sweat turns to water vapour,
which then evaporates.
 Radiation: Exposed parts of the body
radiate (bounce) heat away from body
 Conduction: Clothes and objects in
contact with the skin take up heat.
 Convection: Air passing over exposed
parts of the body become heated, rises
and is replaced by cooler air.
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Effects of Nervous Control
of Temperature
 Body temperature rises.
 Skin capillaries dilate.
 Extra blood near surface increases heat loss
by radiation, conduction and convection.
 Skin is warm and pink.
 Body temperature falls.
 Arteriolar constriction conserves heat.
 Skin is whiter and feels cooler.
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Heat Loss Through Skin
Affected By:
 Difference between body and environmental
temperatures.
 Amount of body surface exposed to air
 Types of clothes worn.
 Several layers of lighter clothes trap more air,
thus provide better insulation against heat
loss than one thick garment.
 A balance is maintained between heat
production and heat loss.
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Nervous Control of Body
Temperature.
 Temperature Regulating Centre in
Hypothalamus is responsive to temperature
in circulating blood.
 Through Autonomic nerve stimulation of
sweat glands when body temperature rises.
 Vasomotor centre in medulla oblongata
controls diameter of arterioles, therefore the
amount of blood circulating in the capillaries
of the dermis.
 Vasomotor centre controlled by temperature
of blood supply and the hypothalamus.
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Sweat Glands.
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Body temperature increases.
Sweat glands stimulated to secrete sweat.
Sweat delivered to surface by ducts.
Sweat then evaporates.
When sweat droplets are visible on skin,
rate of production is exceeding rate of
evaporation.
 Most likely when air is humid and
atmospheric temperature high.
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