The conditions inside our body must be carefully controlled if it is to function effectively. Homeostasis is the maintenance of a constant internal environment in the body. The nervous system and hormones are responsible for controlling this.
The body control systems are all automatic, and involve both nervous and chemical responses. It has many important parts, including:
Body temperature is one of the factors that are controlled during homeostasis. The human body maintains the temperature that enzymes work best, which is around 37°C. This process is controlled by the thermoregulatory centre, which is contained in the hypothalamus in the brain, and it contains receptors sensitive to the temperature of the blood. The skin also has temperature receptors and sends nervous impulses back to the thermoregulatory centre.
When we get too hot:
Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost to the environment. This is called vasodilation.
When we get too cold:
The hairs on the skin also help to control body temperature. The hairs lie flat when we are warm, and rise when we are cold.
If we are too cold nerve impulses are sent to the hair erector muscles which contract. This raises the skin hairs and traps a layer of insulating air next to the skin.
Skin hairs lie flat when we are hot and stand upright when we are cold
The control of body temperature is an example of a negative feedback mechanism. It regulates the amount of:
The amount of blood flowing through the skin capillaries is altered by vasoconstriction and vasodilation.
|Too cold||Too hot|
|Arterioles||Get narrower||Get wider|
|Blood flow in skin capillaries||Decreases||Increases|
|Heat loss from skin||Decreases||Increases|
These diagrams show the processes that take place when vasoconstriction and vasodilation occur.
Vasoconstriction – a response to being too cold