Reproduction and genetics, Year 11: hormones, contraception and fertility

Oestrogen

提示Its name begins with the same letters as "oestrus".

为什么Oestrogen is released by the ovaries in the first half of the cycle and makes the uterus lining grow back. After the egg is released, a second hormone, progesterone, maintains the lining. If the egg is not fertilised, the levels of both fall and the lining is shed.

testosterone

提示Its name begins with the name of the organ that makes it.

为什么At puberty the testes begin to release this hormone. It stimulates the production of sperm and causes the male secondary sex characteristics, such as a deeper voice and facial hair, to develop.

FSH (follicle stimulating hormone)

提示Its three-letter name starts with the word for the small sac in which each egg develops.

为什么Each egg develops inside a small sac in the ovary. This hormone starts that development at the beginning of the cycle, so that one egg is ready to be released about two weeks later.

It stimulates the release of an egg from the ovary (ovulation)

提示It acts about halfway through the cycle, once an egg is mature.

为什么FSH first causes an egg to mature. A surge of LH around the middle of the cycle then makes the ovary release it, after which the egg travels along the oviduct, where it may be fertilised.

It inhibits the release of FSH and stimulates the release of LH

提示It switches one of them off and the other one on.

为什么FSH makes an egg mature and makes the ovaries produce oestrogen. As oestrogen builds up, it stops more FSH being released, so no further eggs mature, and it triggers the LH that causes ovulation. Each hormone in turn controls the next.

Progesterone; it inhibits FSH and LH

提示It is the hormone that maintains the uterus lining in the second half of the cycle.

为什么This hormone is produced in the ovary after the egg has been released. While its level is high the lining is kept in place and no new egg matures or is released. If the egg is not fertilised its level falls, the lining breaks down and a new cycle begins.

The hormones inhibit the production of FSH, so no eggs mature

提示Remember which hormone starts an egg developing at the beginning of each cycle.

为什么FSH is the hormone that makes an egg mature in the ovary. The hormones in the pill stop FSH being produced, so no egg matures and none is released. The pill has to be taken regularly to keep working.

progesterone

提示It is the hormone that is naturally high in the second half of the menstrual cycle.

为什么A steady, slow release of this hormone stops eggs maturing and being released. Depending on the method, one injection, implant or patch goes on working for a number of months or years, so there is no daily pill to remember.

They stop sperm from reaching an egg

提示The name of this group of methods says what is put in the way.

为什么These are non-hormonal methods: they do not change the menstrual cycle, but physically keep sperm and egg apart so that fertilisation cannot happen. Condoms also reduce the risk of passing on sexually transmitted infections.

By preventing an embryo from implanting in the uterus, or by releasing a hormone

提示One way is about the lining of the womb; the other works like the pill.

为什么An intrauterine device is a small device placed inside the uterus by a doctor or nurse. Some kinds stop an embryo settling into the uterus lining and some release a hormone. Once fitted, one goes on working for years.

The choice also depends on personal, ethical and religious views

提示Some questions are about what people believe is right for them, not about what can be measured.

为什么Evidence can compare methods: how well each prevents pregnancy, its side effects, and whether it is permanent, as surgical sterilisation is. But people weigh those facts differently according to their beliefs, their relationships and their plans, so the decision is theirs to make.

FSH and LH; they stimulate eggs to mature and to be released

提示The same pair of hormones prepares and lets go of an egg in a natural menstrual cycle.

为什么Some women do not release eggs regularly because their own levels of these two hormones are too low. Giving the hormones as a drug can restart the process, and the woman may then become pregnant in the normal way.

FSH and LH are given → eggs are collected → eggs are fertilised by sperm in the laboratory → they develop into embryos → one or two embryos are placed in the uterus

提示The middle steps all happen in a dish, outside the body.

为什么The hormones make several eggs mature at once. The eggs are collected from the mother and mixed with the father's sperm in the laboratory. When each fertilised egg has become a tiny ball of cells, one or two are inserted into the mother's uterus.

In vitro fertilisation (IVF)

提示The first two words of its name are Latin for 'in glass'.

为什么In this treatment, eggs are collected from the mother and mixed with sperm in a dish. It is used when eggs and sperm cannot meet inside the body, for example because the oviducts are blocked.

stressful; not high; multiple births

提示Think about the strain on the patient, the chance of it working, and the number of embryos used.

为什么The treatment gives a woman the chance to have a baby of her own, but it is demanding and many attempts do not end in a birth. Because more than one embryo may be placed in the uterus, twins or triplets are more likely, and such pregnancies carry more risk.

Microscopy; eggs, sperm and early embryos are too small to handle and check without a microscope

提示Consider the size of a single egg cell.

为什么In IVF, staff must find the eggs, see whether they have been fertilised and choose healthy embryos when each is only a tiny ball of cells. All of that depends on being able to see and work with single cells clearly.