1. Control of body temperature in humans Learning objectives: Explain how humans and other endotherms regulate their body temperature Explain the role of the hypothalamus in regulating body temperature

2. Mechanisms of heat regulation: Heat gain: Environmental Metabolic Heat Loss: Evaporation Losing to environment Excretion

3. Humans Humans live in a variety of temperatures Like all mammals, humans are endotherms (warm blooded) Human body temperature must remain around 37 degrees Celsius

4. In a cold environment: We must conserve body heat and gain heat to maintain body temperature Vasoconstriction- blood vessels near the surface of the skin narrow, reducing the volume of blood near the surface, reducing the heat lost to the environment from the blood Shivering- Muscles contract to produce heat via metabolic reactions Hair-raising(not so much in humans)- muscles in the skin at the base of each hair contract, raising hairs and trapping air, forming an insulating layer. Increased metabolic rate- respiration increases to generate more heat Sweating reduced Behavioural mechanisms- huddling, sheltering

5. In a hot environment: We must lose body heat to maintain a core temperature Vasodilation- blood vessels near the surface of the skin dilate and increase in volume, allowing more blood to flow through, radiating heat away through the skin Sweating- water evaporates from the surface of the skin, using heat energy to turnt he liquid into water vapour. Prevalent in humans as we lack body hair. In other mammals this takes place from the tongue and mouth Body hair flattening- removes the insulating layer Behaviours- not performing metabolic activity, sheltering.

6. Conserving body temperature Thermoregulation is a form of homeostasis. Temperature (the stimulus) is detected by receptors called thermoreceptors in the skin. This information is passed to a coordinator in the brain called the hypothalamus. An effector- various such as muscles for shivering or in the follicles to raise the hairs, produces a response in order to bring about either an increase or decrease in core body temperature.

7. The hypothalamus The hypothalamus is a structure located in the brain, it has a two parts which monitor body temperature: Heat gain centre- controls mechanisms which increase body temperature Heat loss centre- controls mechanisms which decrease body temperature The hypothalamus receives inputs about body temperature in two ways: it monitors core body temperature by monitoring the temperature of blood passing through it, in addition to monitoring skin temperature by receiving nervous signals from thermoreceptors on the skin. Core temperature is the more important.