1. THERMOREGULATION Control of body temperature © 2008 Paul Billiet ODWSODWS

2. Core temperature The core temperature of the human body is 37°C The core of the human body includes the organs of the thorax, abdomen and the head This is where the vital organs are located Their enzyme systems must operate in optimum conditions The periphery of the body can withstand some deviation from the core temperature © 2008 Paul Billiet ODWSODWS

3. Heat loss and heat gain The body must balance its heat budget Heat is gained: by conduction from warm air surrounding the body by the bodys metabolic activity which generates heat e.g. when muscle move Heat is lost: by conduction and radiation to cold air (or water) by evaporation of sweat from the body surface (c.f. properties of water) Humans can also affect their body temperature by changing their behaviour e.g. wearing different clothes, seeking shade © 2008 Paul Billiet ODWSODWS

4. Maintaining the body temperature Keeping warmStaying cool Increased insulation, subcutaneous fat reduces the conduction of heat from the body Increase blood flow to skin, increases conduction and radiation of heat from the body Reduced sweating decreases evaporation Increased sweat secretion, increases evaporation Increased shivering, increases heat produced by muscle tissue 2 to 5 times Reduced activity © 2008 Paul Billiet ODWSODWS

5. nerves Less heat generated More water covers the skin. More evaporation Skin arteries dilate More blood to the skin. More radiation & conduction of heat Muscles of skin arteriole walls relax Sweat glands increase secretion Muscles reduce activity Core body temperature >37°C Hypothalamus Thermoreceptors © 2008 Paul Billiet ODWSODWS

6. Thermoreceptors Return to 37°C Muscles of skin arteriole walls relax Core body temperature >37°C Hypothalamus Sweat glands increase secretion nerves Muscles reduce activity Thermoreceptors NEGATIVE FEEDBACK Blood temperature Body loses heat © 2008 Paul Billiet ODWSODWS

7. nerves More heat generated Less water covers the skin. Less evaporation Skin arteries constrict Less blood to the skin. Less radiation & conduction of heat Muscles of skin arteriole walls constrict Sweat glands decrease secretion Muscles shivering nerves Core body temperature <37°C Thermoreceptors Hypothalamus © 2008 Paul Billiet ODWSODWS

8. Thermoreceptors Return to 37°C NEGATIVE FEEDBACK Blood temperature Body loses less heat Body gains heat Muscles of skin arteriole walls constrict Core body temperature <37°C Sweat glands decrease secretion nerves Muscles shivering Thermoreceptors Hypothalamus nerves © 2008 Paul Billiet ODWSODWS