1 Access Human Biology. Temperature Regulation.

2 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.

3 The Liver.  High metabolic activity (very busy!).  Heat produced as a bi-product.  Metabolic rate thus heat are increased after eating.

4 Body Temperature.  Normal body temperature 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.

5 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.

6 Digestion.  Digestive organs produce heat during peristalsis.  Chemical reactions during digestive process also cause heat production.

7 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

8 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.

9 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.

10 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.

11 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.

12 Sweat Glands.  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.