Hormones and glands

Hormones are chemicals secreted by glands in the body. Different hormones affect different target organs. The bloodstream transports hormones from the glands to the target organs.

Move the mouse over the different glands to see what they do.

Hormones regulate the functions of many cells and organs

The target organ and effects of glands and hormones

Control of internal conditions

It is important that the internal environment of the body is controlled. Maintaining a constant internal environment is called homeostasis. The nervous system and hormoneshormones: Chemical messengers produced in glands and carried by the blood to specific organs in the body are responsible for this. These are some of the internal conditions that are controlled.

Water content of the body

This is controlled to protect cells by avoiding too much water entering or leaving them. Water content is controlled by water loss from:

• the lungs when we exhale
• the skin by sweating
• the body, in urine produced by the kidneys

Ion (salts) content of the body

This is controlled to protect cells by avoiding too much water entering or leaving them. Ion content is controlled by loss of ions from:

• the skin by sweating
• the body in urine produced by the kidneys

Temperature of the body

This is controlled to maintain the temperature at which enzymesenzymes: Proteins which catalyse or speed up chemical reactions inside our bodies work best. Body temperature is controlled by:

• controlling blood flow to the skin
• sweating
• shivering

Blood sugar levels

This is controlled to provide cells with a constant supply of energy. Blood sugar level is controlled by the release and storage of glucose controlled by insulininsulin: A hormone that regulates the level of sugar in the blood. It is produced in the Islets of Langerhans, in the Pancreas..

Hormones in the menstrual cycle

The menstrual cycle in women is a recurring process in which the lining of the uterus - womb - is prepared for pregnancy, and if pregnancy does not happen, the lining is shed at menstruation.

Several hormoneshormones: Chemical messengers produced in glands and carried by the blood to specific organs in the body control this cycle, which includes controlling the release of an egg each month from an ovary, and changing the thickness of the uterus lining. These hormones are secreted by the ovaries and pituitary gland.

FSH

The hormone FSH is secreted by the pituitary gland. FSH makes two things happen:

1. it causes an egg to mature in an ovary
2. it stimulates the ovaries to release the hormone oestrogen

Oestrogen

The hormone oestrogen is secreted by the ovaries. Oestrogen makes two things happen:

1. it stops FSH being produced - so that only one egg matures in a cycle
2. it stimulates the pituitary gland to release the hormone LH

LH

The hormone LH causes the mature egg to be released from the ovary.

This image shows how the level of oestrogen changes during the menstrual cycle. Progesterone is another hormone secreted by ovaries: it maintains the lining of the uterus and stays high during pregnancy.

Hormone levels during the mentrual cyle

This animation shows how the levels of FSH and LH change during the menstrual cycle.

Controlling fertility

Human fertility is controlled by hormoneshormones: Chemical messengers produced in glands and carried by the blood to specific organs in the body. This means that knowledge of hormones can be used to decide to increase, or reduce, the chances of fertilisation and pregnancy.

Oral contraceptives

Contraceptive pills

The oral contraceptive, 'the pill', greatly reduces the chances of mature eggs being produced. The pill contains oestrogen, or oestrogen and progesterone. These hormones inhibit the production of FSH, which in turn stops eggs maturing in the ovaries.

Fertility treatment

Some women have difficulty becoming pregnant because they don't produce enough FSH to allow their eggs to mature. 'Fertility drugs' contain FSH, which stimulates eggs to mature in the ovary.

Benefits and problems of controlling fertility

Oral contraceptives

Oral contraceptives allow couples to choose the time they start a family, and choose the time they stop having children.

However, some women who take the pill may suffer from changes in weight, mood and blood pressure, as a result of the hormones in it. There is also a chance of an increased risk of developing blood clots. On the other hand, there is evidence of a decreased risk of developing cancer of the uterus or ovaries.

Fertility treatment

Fertility treatments increase a woman's chance of becoming pregnant, although the treatment may not always work. On the other hand, because the treatment boosts the production of mature eggs, multiple conceptions sometimes occur, with twins or triplets being expected. This increases the risk of complications in pregnancy and childbirth, and may lead to premature or underweight babies.

IVF

If a couple are having difficulty conceiving a child because the quantity or quality of the man’s sperm is poor then in vitro fertilisation - or 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.

IVF - In vitro fertilisation

Some people worry about the ethical implications of IVF, and are concerned that couples may only want fertilised eggs with 'desirable' qualities. 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.

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