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| 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 | The internal environment of the body is controlled by the nervous system and hormones. The maintenance of a constant internal environment is called homeostasis. Below are some of the internal conditions that need to be controlled. |
| 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. | Ion levels are controlled to protect cells from too much water entering or leaving them. Ion content is controlled by the loss of ions from: 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. | 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 insulin. |
| 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 menstrual cycle in women is a recurring monthly process in which the lining of the uterus (the womb) is prepared for pregnancy. If pregnancy does not happen, the lining is shed at menstruation. Several hormones 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. |
| 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. | The hormone oestrogen is secreted by the ovaries. Oestrogen makes two things happen: it stops FSH being produced - so that only one egg matures in a cycle it stimulates the pituitary gland to release luteinizing hormone (LH), which triggers ovulation (the release of the mature egg from the ovary). |
| 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. | The oral contraceptive, commonly known as the pill, greatly reduces the chances of mature eggs being produced. It contains oestrogen or progesterone (another hormone). These hormones inhibit the production of FSH, which in turn stops eggs maturing in the ovaries. |
| 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. | Some women have difficulty becoming pregnant because they don't produce enough FSH to allow their eggs to mature. Fertility drugs contain FSH and LH, which stimulate eggs to mature in the ovary. 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. |
| 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. |
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| 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. | Biology 1- Control in the human body |
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