Control of body temperature THERMOREGULATION Control of body temperature © 2016 Paul Billiet ODWS

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 © 2016 Paul Billiet ODWS

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 body’s 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 © 2016 Paul Billiet ODWS

Maintaining the body temperature Keeping warm Staying 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 © 2016 Paul Billiet ODWS

Muscles of skin arteriole walls relax Core body temperature >37°C Thermoreceptors Hypothalamus nerves Muscles of skin arteriole walls relax Sweat glands increase secretion Muscles reduce activity Skin arteries dilate More blood to the skin. More radiation & conduction of heat More water covers the skin. More evaporation © 2016 Paul Billiet ODWS Less heat generated

Muscles of skin arteriole walls relax NEGATIVE FEEDBACK Blood temperature Muscles of skin arteriole walls relax Core body temperature >37°C Hypothalamus Sweat glands increase secretion nerves Muscles reduce activity Thermoreceptors Thermoreceptors Body loses heat Return to 37°C © 2016 Paul Billiet ODWS

Muscles of skin arteriole walls constrict Core body temperature <37°C Thermoreceptors nerves Hypothalamus Muscles of skin arteriole walls constrict nerves Sweat glands decrease secretion Skin arteries constrict Less blood to the skin. Less radiation & conduction of heat Muscles shivering Less water covers the skin. Less evaporation More heat generated © 2016 Paul Billiet ODWS

Muscles of skin arteriole walls constrict NEGATIVE FEEDBACK Blood temperature Muscles of skin arteriole walls constrict Core body temperature <37°C Sweat glands decrease secretion nerves Muscles shivering Thermoreceptors Hypothalamus Thermoreceptors Body loses less heat Return to 37°C Body gains heat © 2016 Paul Billiet ODWS