Thermoregulation

Maintaining Body Temperature

Humans control their body temperature in a process called thermoregulation. It is essential the internal body temperature is maintained at 37\degree \text{C} in order for enzymes to work effectively. 

Heat energy is released into the body during respiration and then lost into its surroundings. The amount of heat energy lost and gained is regulated by the thermoregulatory centre in the hypothalamus of the brain and ensures a constant internal body temperature is maintained.

This process is controlled in a negative feedback cycle:

1. Temperature receptors in the thermoregulatory centre detect that the temperature of the blood is too high or too low. Temperature receptors on the skin also detect the change in body temperature send electrical nerve impulses to the thermoregulatory centre. 
2. The thermoregulatory centre will then coordinate a response and send impulses to specific effectors.
3. Effectors will produce responses that will increase or decrease body temperature accordingly, returning it back to normal. 

Increasing and Decreasing Body Temperature

Effectors produce responses when sent impulses from control centres.

Temperature too high

When the the body is too hot it needs to lose more heat energy than it is producing to bring the temperature back down. The thermoregulatory centre sends impulses to effectors near the surface of the skin to increase heat loss:

• Sweat glands increase sweat production which evaporates from the skin, transferring the heat energy into the environment. 
• Blood vessels near the surface of the skin will dilate (widen) to allow blood to flow even closer to the surface of the skin. This is called vasodilation and helps heat energy get transferred into the environment.

Temperature too low

When the the body is too cold it needs to reduce heat loss to bring the temperature back up. The thermoregulatory centre sends impulses to effectors near the surface of the skin to prevent heat loss:

• Sweat glands stop producing sweat to minimise energy transfer to the environment. 
• Blood vessels near the surface of the skin will constrict to reduce the blood flow to the surface of the skin. This is called vasoconstriction and further prevents heat energy being lost into the environment.
• Hairs stand on end to trap air that insulates the body.
• Skeletal muscles start to contract automatically (shivering) to increase respiration and therefore heat energy production.