Controlling body temperature

In a nutshell

Body temperature must be kept constant. To do this, the body must balance the amount of energy gained and lost. Receptors in the brain detect changes in temperature and coordinate an appropriate response to heat or cool the body. The skin has special structures that allow it to carry out these responses.

Controlling body temperature

It is important to control body temperature because enzymes in the body are most active at $37\ \degree C$ . The process that keeps the core body temperature at $37\ \degree C$ is called thermoregulation. This is controlled by the hypothalamus which produces hormones that trigger skin and muscle changes. The thermoregulatory centre in the hypothalamus of the brain, monitors and controls body temperature. Different responses are produced by effectors to counteract an increase or decrease in body temperature.

Some effectors work antagonistically, meaning they perform opposite functions. This allows a more sensitive response.

Example

One effector heats and one effector cools. This will achieve a very precise temperature.

Hot environment or exercise

1.	Body temperature rises.
2.	The hypothalamus detects the rise and causes a response.
3.	Changes are triggered in blood flow, this causes more blood to flow near the skin's surface.
4.	Sweat glands release more sweat onto the surface of the skin to evaporate.
5.	Sebaceous glands produce oil that helps sweat to spread over the skin.
6.	There is an increased transfer of energy to the surroundings.

Cold environment

1.	Body temperature falls.
2.	The hypothalamus detects the fall and causes a response.
3.	Changes are triggered in blood flow, so less blood flows near the skin's surface.
4.	Sweat glands stop producing sweat.
5.	Body hairs are raised by erector muscles in the skin (goosebumps).
6.	There is a reduced transfer of energy to the surroundings.

Skin

Biology; Animal coordination, control and homeostasis; KS4 Year 10; Controlling body temperature — The structures of the skin include the 1. epidermis, 2. the dermis, 3. blood capillaries, 4. sweat glands, 5. blood vessels, 6. hair muscles, 7. body hair. Some of these structures are specialised and change in response to cold or hot conditions.

Sweat gland	Releases sweat when losing heat by evaporation.
Blood capillary	Blood flow through surface capillaries changes depending on temperature. (Vasodilation or vasoconstriction).
Hair muscle	The hair muscle contracts when cold to pull hairs upright, this traps an insulating layer. When it is warm, hairs lie flat.

Vasoconstriction

Vasoconstriction occurs when you are cold. More blood flows through deep skin blood vessels, so less blood flows through surface capillaries. This keeps warm blood deeper in the skin so less heat will be transferred to the air.

Vasodilation

Vasodilation occurs when you are hot. Less blood flows through deep skin blood vessels and more blood flows through surface capillaries, increasing the flow of warm blood by the skin and causing heat loss to the air by radiation.