Edexcel Biology Gcse - Hormones in Human Reproduction Part 2

1) Menstruation

2) Linging of the uterus builds up.

Egg is released.

3) Lining maintaining.

4) Lining breaks down (menstruation)

The pituitary gland produces FSH which causes the development of a follicle in the ovary.

As the egg develops inside the follicle, the follicle produces the hormone oestrogen.

The oestrogen causes growth and repair of the lining of the uterus wall.

Oestrogen inhibits FSH

When oestrogen rises to a high enough level it causes a surge in LH from the pituitary which causes ovulation where an egg is released from the follicle (Day 14 of the cycle).

The follicle becomes the corpus luteum and this produces oestrogen and progesterone which inhibit FSH and LH production by the pituitary. This is an example of negative feedback.

Progesterone maintains the uterus lining (the thickness of the uterus wall).

If the egg has not been fertilised, the corpus luteum dies and progesterone levels drop. This causes menstruation, where the uterus lining breaks down - this is known as having a period.

The pituitary gland produces FSH which causes the development of a follicle in the ovary.

As the egg develops inside the follicle, the follicle produces the hormone oestrogen.

The oestrogen causes growth and repair of the lining of the uterus wall. Oestrogen inhibits FSH.

When oestrogen rises to a high enough level it causes a surge in LH from the pituitary which causes ovulation where an egg is released from the follicle (Day 14 of the cycle).

The follicle becomes the corpus luteum and this produces oestrogen and

progesterone which inhibit FSH and LH production by the pituitary. This is an example of negative feedback.

Progesterone maintains the uterus lining (the thickness of the uterus wall).

If the egg has not been fertilised, the corpus luteum dies and progesterone levels drop. This causes menstruation, where the uterus lining breaks down - this is known as having a period.

If a woman becomes pregnant, the placenta produces progesterone. This maintains the lining of the uterus during pregnancy and means that menstruation does not happen.

Pituitary gland

Ovaries

Pituitary gland

Ovaries

Causes an egg to mature in an ovary. Stimulates the ovaries to release oestrogen.

Stops FSH being produced (so that only one egg matures in a cycle). Repairs, thickens and maintains the uterus lining. Stimulates the pituitary gland to release LH.

Triggers ovulation (the release of a mature egg).

Maintains the lining of the uterus during the latter part of the menstrual cycle and during pregnancy.

Human fertility is controlled by hormones, so fertility can be controlled using hormonal forms of contraception.

The oral contraceptive, which is known as the pill, contains oestrogen or progesterone or a combination of both hormones. These hormones inhibit the production of FSH, and eggs cannot mature.

Oestrogen at low levels stimulates the release of eggs. However at high doses, oestrogen will inhibit FSH production. After taking the pill for a while, egg development and release will stop completely. If there is no egg available, there can be no baby. This is why contraceptive pills are so effective.

Oral contraceptives are more than 99% effective if taken correctly and can reduce the risk of certain cancers.

However, there are possible side effects, such as changes in weight, mood and blood pressure due to high levels of oestrogen. Modern pills contain much less oestrogen.

Contraceptive injections, implants or skin patches contain slow release progesterone to inhibit the maturation and release of eggs.

physical barrier methods such as condoms and diaphragms, which prevent the sperm reaching an egg

intrauterine devices (IUD) also known as a coil, prevent the implantation of an embryo or release of a hormone

spermicidal agents which kill or disable sperm

abstaining from intercourse when an egg may be in the oviduct

surgical methods of male and female sterilisation - an example is a vasectomy, where the sperm ducts are cut and tied

condoms are easy and quick to use, but sometimes they can tear or rip

diaphragms need to be put in just before sex and left in several hours afterwards

IUDs need to be fitted by a health professional - IUD can remain in position for up to 10 years, however there is a small risk of causing an ectopic pregnancy

spermicidal agents can be added to other physical barriers such as condoms, but some people can have allergic reactions to these

abstaining can be used successfully, but if the timings are not accurate the chance of pregnancy is high

surgical methods cannot be reversed, and is considered permanent

Assisted Reproductive Technology is the use of hormones and procedures, as fertility treatments, to help to achieve pregnancy. These include in vitro fertilisation (IVF) and a fertility drug, clomifene.

Some women have difficulty becoming pregnant because they don't produce enough FSH to allow their eggs to mature. Some 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, it increases the chance of twins or triplets. Multiple pregnancies carry a risk of complications, and may lead to premature or underweight babies.

Intracytoplasmic Sperm Injection (ICSI) is a specialised method of IVF

If a couple are having difficulty conceiving a child because there are issues with the quality of the man's sperm, or a woman has blocked oviducts, then IVF can be used.

IVF involves giving a mother FSH and LH, to stimulate the maturation of several eggs in the ovary

the eggs are collected from the mother and fertilised by sperm from the father in a dish in the laboratory

the fertilised eggs develop into embryos

at the stage when they are tiny balls of cells one or two embryos are inserted into the mother's uterus (womb)

Some women have difficulty becoming pregnant because they do not ovulate (release eggs).

Clomifene is a drug used as a fertility drug to stimulate ovulation, the release of eggs. It works by blocking the action of oestrogen's negative feedback on LH. Therefore more LH is released in a surge. This mimics the LH surge which occurs just before ovulation.

Oestrogen

Progesterone

menstruation

Pituitary gland