In order to remember the definition of homeostasis it is useful to memorise the mnemonic ‘MACIE’; the Maintenance of A Constant Internal Environment. Conditions in the body must be constantly controlled because cells depend on the body’s environment to live and function. The maintenance of the conditions by homeostasis is very important because in the wrong body conditions certain processes (osmosis) and proteins (enzymes) will not function properly.
Conditions that must be controlled include temperature, blood sugar level and water content and they are all controlled by different hormonal and nervous systems.
For example, the maintenance of body temperature is controlled by the brain. The body’s temperature must be kept at 37 degrees because this is the temperature at which enzymes optimally function.
Temperature receptors in the skin detect changes in the external environment and pass this information on to the brain’s processing centre, the hypothalamus. The hypothalamus itself also has receptors that detect changes in the blood temperature. If the external/internal temperature changes, the hypothalamus will automatically trigger changes in the body’s effectors (sweat glands and muscles) to keep our temperature constant.
If we are too hot; glands in the skin secrete sweat onto the surface to increase heat loss by evaporation.
If we are too cold; arrector pilli muscles in the skin contract and cause the hair on our arms to stand up straight, trapping a layer of warm air next to the skin to reduce heat loss. It is the contraction of these muscles that causes the appearance of goosebumps when we’re cold.