Hormones are chemical substances that regulate processes in the body. Hormones are secreted by glands and travel to their target organs in the bloodstream. Several hormones are involved in the female menstrual cycle. Hormones can be used to control human fertility and have advantages and disadvantages

Water in the body has to be controlled to protect cells from either too much water entering or too much water leaving them. Water content is controlled by water loss from:
the lungs - when we exhale
the skin - through sweating
passing urine - produced by the kidneys.

This is controlled to maintain the temperature at which enzymes work best. Body temperature is controlled by sweating, shivering, and controlling blood flow to the skin.

Hormones are chemicals secreted by glands in the body. Different hormones affect different target organs. The bloodstream usually transports hormones from the glands to their target organs. Hormones regulate the functions of many cells and organs.

The hormone FSH is secreted by the pituitary gland. FSH makes two things happen:
it causes an egg to mature in an ovary
it stimulates the ovaries to release the hormone oestrogen.

Human fertility is controlled by hormones. This means that knowledge of hormones can be used to decide to increase, or reduce, the chances of fertilisation and pregnancy.

Oral contraceptives allow couples to choose the time they start a family, and choose the time they stop having children.
The first birth-control pills contained higher amounts of oestrogen than the pills taken today. This caused women to have significant side effects, such as changes in weight, mood and blood pressure. Modern birth-control pills contain much less oestrogen. Some only contain progesterone, which also leads to fewer side effects.

If a couple are having difficulty conceiving a child because the quantity or quality of the man’s sperm is poor then IVF can be used. This is where the egg is fertilised outside the woman’s body and then implanted back into her uterus. As FSH can also be used to encourage the production of several mature eggs at once, it is used as part of IVF to increase the number of eggs available for fertilisation.

Some people worry about the ethical implications of IVF. They are concerned that couples may want 'designer babies' with 'desirable' qualities, so may only want certain fertilised eggs. For example, they may want a girl if they have lots of boys in the family, or they may wish to avoid producing a baby with an inherited defect.