Detecting Temperature Change Internal (core) body temperature is kept constant within a narrow range of about 37 - 38 Changes to internal body temperature are detected by hot and cold receptors in the: –Skin –Hypothalamus –Spinal cord –Large veins –Parts of the digestive system Receptors Receptors are made up of sensory neurons also called affector neurons Internal External

Detecting Temperature Change Changes in the external temperature cause changes in the temperature of exposed skin These changes are detected by 2 different types of receptors located just under the skin: –Hot – these receptors detect heat by increasing electrical impulses to the hypothalamus –Cold – these send more electrical impulses when cold.

Detecting Temperature Change

Causes of temperature change To maintain a stable core temperature: Heat Production = Heat Loss This is controlled by the hypothalamus

Heat Production The body constantly produces heat through: –Cellular respiration The body is able to increase body temperature by: –Shivering –Movement –Increased metabolism –Raising the hair on skin surface Piloerection - trapping warm air close to the skin’s surface and reduces heat loss –Reducing blood flow to skin Vasoconstriction } (all of these things increase the rate of cellular respiration)

Heat Loss Heat is lost by the body through a range of processes: –Radiation –Conduction –Convection –Evaporation The body is able to reduce body temperature by: –Increased sweating –Increased blood flow to skin’s surface Vasodilation –Decreased metabolism } Heat is transferred from warmer objects to colder objects (a bit like diffusion) (both of these occur due to the temperature difference (gradient) between our warm bodies and the air at the skin’s surface When heat is lost in energy waves When heat is lost to the air due to direct contact with skin Even without sweating, water is lost from skin continually, causing a cooling effect Movement of air which maintains the temperature gradient

Heat loss Heat gain Expired air Urine faeces sweat Panting Radiation Conduction Convection behaviour Radiation Conduction Convection Metabolism Vasodilation Vasoconstriction

Vasodilation - capillaries increase in size to increase SA for heat to be lost (usually causes skin to appear pink/red - flushed) Vasoconstriction - capillaries decrease in size in decrease SA for heat to be lost (usually causes skin to appear purple/blue)

Sweating Water evaporates. For liquid to change to a gas state heat is needed. As sweat evaporates it uses body heat to turn it into a gas. Shivering Uncontrolled muscle spasms. Muscle contraction requires energy (ATP) therefore cellular respiration will increase - a reaction that produces 60% heat.

Piloerection Hairs stand on end producing goose bumps trapping a layer of heat around the body. Thyroxine Hormone that increases or decrease the metabolic rate. Pituitary gland stimulates the thyroid gland to increase/decrease production of thyroxine.

Insulation - fur, blubber feathers. Decreasing SA - roll into ball sleeping together in nests. Behavioural - take clothing off, seek shade jump around.

Normal Body Temperature 37°C Body temperature increases Body temperature decreases Sweating panting Vasodilation Decrease in Thyroxine decrease SA Burrow Shivering Vasoconstriction Increase in Thyroxine Increase SA Piloerection

TRH = thyrotropin releasing hormone TSH = Thyroid stimulating hormone