Access Human Biology Temperature Regulation 1 Heat Production

Access Human Biology. Temperature Regulation. 1

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. 2

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

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. 4

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. 5

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

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 7

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. 8

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. 9

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. 10

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. 11

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. 12