Thermoregulation

• maintaining the equal proportion of heat gained by the body compared to heat lost by the body is thermoregulation
• factors which increase body temperature are exercise or strenuous activity and sickness (fever)
• the rate at which energy is released by the breakdown of food is called the metabolic rate
• radiation is a type of heat transfer where heat is transferred from one object to another without the objects being in contact, e.g. the sun or heaters
• conduction is a type of heat trasnfer where heat is transferred from one object to another by physical contact, e.g. hand in hot water
• convection heat transfer is when cool air in contact with the body is warmed then carried away by convection currents, e.g. air conditioner
• evaporation is a type of heat transfer where heat is removed from the body when liquid is converted to vapour, e.g. sweating
• peripheral thermoreceptors are found in the skin and mucous membranes, detecting information from the external environment. They can be hot or cold
• hot peripheral thermoreceptors detects higher than normal temperature in the environment and the body will try to reduce heat production and increase heat loss
• cold peripheral thermoreceptors detects a lower than normal temperature in the environment so the body will try to increase heat production and decrease heat loss
• central thermoreceptors are found in the hypothalamus. When the body detects higher or lower temperatures the hypothalamus will try and initiate heat conservation of stimulate heat loss. These are to do with the physiological mechanisms of regulating body temperature
• changes in the skin increases or decreases the rate at which heat is lost from the body through the use of blood vessels increasing or decreasing blood-flow to the skin
• feeling cold:

  • preventing falling body temperature
  • tiny hairs on our body are raised and will stick up
  • vasoconstriction - blood vessels reduce blood-flow to the skin
  • hypothalamus sends a nerve impulse via sympathetic nerves to reduce blood-flow
  • sweat glands reduce their activity of producing sweat
• feeling hot:

  • preventing rising body temp
  • tiny hairs on our body will lie flat on the surface of our skin
  • vasodilation - blood vessels dilate increasing blood-flow - causes skin to become red
  • most heat is lost via radiation and convection
  • sweat glands increase sweat production
  • production and transport of sweat to the surface is stimulated by sympathetic nerves
  • heat is removed from the skin as sweat evaporates
• Hot conditions for skin:

  1. hot receptors have been detected by PNS
  2. hypothalamus sends out nerve impulses to help decrease body temperature form rising
  3. sympathetic nerves are stimulated to open the sweat glands to release sweat onto the skin to help cool skin down
  4. evaporation of the sweat turns it into water vapour which allows cooling to occur
  5. autonomic nerves have stimulated the diameters of blood vessels to widen, called vasodilation - increases blood-flow to the capillaries to release heat via radiation
  6. heat loss can also be through conduction
• hyperthermia:

  • a body temperature greater than 40
  • when the body absorbs or generates more heat than it can release
  • hot, red,dry skin; fast, strong pulse; headaches, dizziness, nausea, confusion; losing consciousness
  • treatment by continuous application of cold water to the skin, ice packs applied to neck, groin and armpits
• Hypothermia:

  • a body temperature below 35 (significant drop)
  • caused by prolonged exposure to very cold temperatures
  • uncontrollable shivering, exhaustion, cool and pale skin, fumbling hands, confusion and drowsiness
  • treatment by removal from cold environment and take off cold/wet clothes, put on warm clothes and blankets, warm and sweet but not alcoholic drinks
  • rewarm the body at 0.5 to 2 degrees per hour
• humans can respond to heat or cold in two ways:

  • behavioural - where we consciously change our behaviour
  • physiological - where our body automatically alters its functioning without conscious control
• behavioural response to hot:

  • increase in surface area by spreading out
  • remove any clothing, e.g. jumper
  • turn on fan or air conditioner
  • drink cool liquids
• physiological response to hot:

  • sympathetic nerves stimulate increase in sweat production - increases heat loss via evaporation of sweat off the skin
  • peripheral vasodilation increases heat loss via radiation
  • decrease in metabolic rate decreases heat gain be cellular respiration
• behavioural response to cold:

  • reduction of surface area by curling up into a ball (reduces heat loss via radiation)
  • put on a jumper - reduces heat loss via radiation
  • shelter yourself from the wind - reduces heat loss via radiation
  • increase in physical activity causes an increase in aerobic respiration and therefore increase in heat production
  • drink warm fluids
• physiological response to cold:

  • shivering - contraction of skeletal muscles have been stimulated by nerve impulse which causes an increase in heat production
  • peripheral vasoconstriction decreases heat loss via radiation
  • increase in thyroxine secretion causes an increase in metabolic rate and increase in heat production
• Negative feedback loop of high body temperature

  1. Stimulus - increase in body temperature due to external environment

  2. Receptor - hot peripheral thermoreceptor in skin, central thermoreceptor in hypothalamus

  3. Modulator - hypothalamus sends information via nerve impulse and hormonal systems to effectors, medulla oblongata (vasomotor centre)

  4. Effectors - blood vessels in skin, sweat glands, body cells

  5. Response - peripheral vasodilation of blood vessels, increase in sweating which causes evaporation, heat is lost via radiation/convection, behavioural - seek coold spot, remover clothing

  6. Feedback - decrease in body temperature
• Negative feedback loop of low body temperature


  1. Stimulus - decrease in body temperature due to external environment

  2. Receptor - cold peripheral thermoreceptor in skin, central thermoreceptor in hypothalamus

  3. Modulator - hypothalamus sends information via nerve and hormonal systems to effectors, medulla oblongata (vasomotor centre)

  4. Effectors - skeletal muscles, blood vessels in skin, body cells

  5. Response - shivering generates heat production in muscles, vasoconstriction of blood vessels reduces heat loss via radiation, increase in thyroxine causes increase in metabolic rate and therefore heat production, behavioural - turn heater on, put jumper on
• homeostasis


  the process whereby the body's internal environment is maintained in a steady state (with normal tolerance limits)
• the body must regulate:

  • core temperature
  • pH and concentrations of dissolved substances in the body fluids
  • concentration of glucose in blood
  • concentration of oxygen and carbon dioxide in the blood and other body fluids
  • concentration of metabolic wastes
• if the conditions inside the body change, the body automatically switches on control mechanisms that restore the optimal operating environment
• negative feedback


  in homeostatic mechanisms, the response has the effect of reducing or eliminating the stimulus that caused it
• positive feedback


  the response to a stimulus is intensified