B1aL4 Reproductive Hormones and Fertility

Key Words

Uterus - the womb, where the baby grows.

Grade E

The female reproductive cycle is governed by hormones secreted by her brain and by her ovaries.  The hormone levels of a number of different hormones rise and fall in a regular pattern called the menstrual cycle.  It average length is 28 days.  On the days before the menstrual period, many women suffer pre-menstrual tension, an unpleasant combination of soreness and feeling bloated.  These are accompanied by moodiness and irritability.  Every 28 days, there is a menstrual period, characterised by bleeding from the vagina ("time of the month"):

• Between days 0 and 5, menstruation occurs,  The old egg leaves the body.

• Between days 5 and 12, the wall of the uterus (the endometrium) thickens.

• Between days 0 and 12, an egg matures in the ovary,

• Between days 12 and 16, the egg is released.  This is when a woman is most fertile. 

• The egg takes several days to travel from the ovary to the uterus.

• Between days 20 and 28, the egg is in the uterus.

This is summed up in the diagram:

The menstrual cycle is controlled by four hormones:

• Luteinising Hormone (LH);

• Follicle Stimulating Hormone (FSH);

• Oestrogen;

• Progesterone.

The hormone oestrogen is also used in the contraceptive pill.  If the level remains high, the production of FSH is reduced, so the eggs do not mature.  However it takes some days to work.  In this period, other contraceptive methods should be employed.

Grade C

The function of the hormones is shown in this table:

The diagram shows how the hormones oestrogen and progesterone act together to control the menstrual cycle.

Fertility can be stimulated by treating a woman with FSH.  This stimulates egg production, and multiple births may occur.  In 1983, a Liverpool couple, Graham and Janet Walton had this fertility treatment, and became parents to no less than six baby girls.  They all survived and the women are now in their late twenties. 

If fertility treatment does not work, there is a procedure called In Vitro Fertilisation (IVF).  The procedure is:

• Fertility hormones are used.

• A small number of eggs are removed from the woman.  This requires an operation.

• The man provides a sample of sperm.

• The sperm and eggs are mixed together in sterile cell culture medium.

• The embryos are kept in an incubator, and checked regularly.

• Some embryos are stored in liquid nitrogen.

• Typically 2 - 3 embryos are put into the uterus.

If they implant, the pregnancy proceeds as normal.  However, the procedure is not always successful.

Grade A

The levels of hormones vary in a coordinated way during the menstrual cycle.

The hormones act like this:

• Oestrogen rises steadily from day 0 to day 11.  It then falls off rapidly before ovulation at day 14.  It then rises slightly during the next seven days, before falling back to its original level.

•  FSH stimulates the ovary to secrete oestrogen.  The levels of oestrogen follow the varying levels of FSH.

• The LSH spike causes ovulation.

• The progesterone level rises after ovulation, and the result is that the uterus wall grows thicker.

The advantages and disadvantages of IVF need to be considered:

Advantages:

• Childless couples have a chance of having a child;

• Embryos can be selected to ensure that the child does not have an inherited genetic condition.

Disadvantages:

• IVF is not always successful;

• The woman needs to have an invasive procedure.

• Multiple births can occur.

• The procedure can be abused to select designer babies.

The ethics of IVF are closely regulated, as it has been a controversial procedure.