B1.2.2 Control in the Human Body (Part 1 ) : Notes and Active links

Students should know that ......

a) Internal conditions that are controlled include:

■ the water content of the body – water leaves the body via the lungs when we breathe out and via the skin when we sweat to cool us down, and excess water is lost via the kidneys in the urine

■ the ion content of the body – ions are lost via the skin when we sweat and excess ions are lost via the kidneys in the urine

■ temperature – to maintain the temperature at which enzymes work best

■ blood sugar levels – to provide the cells with a constant supply of energy.

b)  Many processes within the body are coordinated by chemical substances called hormones. Hormones are secreted by glands and are usually transported to their target organs by the bloodstream.

c)  Hormones regulate the functions of many organs and cells. For example, the monthly release of an egg from a woman’s ovaries and the changes in the thickness of the lining of her womb are controlled by hormones secreted by the pituitary gland and by the ovaries

d) Several hormones are involved in the menstrual cycle of a woman. Hormones are involved in promoting the release of an egg:

■ follicle stimulating hormone (FSH) is secreted by the pituitary gland and causes eggs to mature in the ovaries. It also stimulates the ovaries to produce hormones including oestrogen

■ luteinising hormone (LH) stimulates the release of eggs from the ovary

■ oestrogen is secreted by the ovaries and inhibits the further production of FSH.