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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 are made up of sensory neurons also called affector neurons External Internal 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 (all of these temperature by: – Shivering – Movement – Increased metabolism } things increase the rate of cellular respiration) – 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 Heat Loss Heat is transferred from warmer objects to colder objects (a bit like diffusion) • Heat is lost by the body through a range of processes: When heat is lost in energy waves – Radiation When heat is lost to the air due to direct (both of these due to contactoccur with skin – Conduction the temperature difference Movement of air which maintains the (gradient) between our warm – Convection temperature gradient bodies and the air at the – Evaporation Even without sweating, water is lost from skin skin’s surface } continually, causing a cooling effect • The body is able to reduce body temperature by: – Increased sweating – Increased blood flow to skin’s surface • Vasodilation – Decreased metabolism Vasodilation Urine Radiation behaviour sweat faeces Conduction Expired air Heat loss Panting Convection Conduction Radiation Convection Heat gain Metabolism 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. •Sweating panting •Vasodilation Body temperature increases •Decrease in Thyroxine •decrease SA •Burrow Normal Body Temperature 37°C Normal Body Temperature 37°C •Shivering Body temperature decreases •Vasoconstriction •Increase in Thyroxine •Increase SA •Piloerection