Biology Edexcel Topic 7 (Menstrual cycle and fertility)

7.4 to 7.8

What is the menstrual cycle

The cycle in women (usually lasting 28 days) that involves the shedding of uterus lining (menstruation), repair of uterus lining, release of an egg (ovulation) and maintenance of the uterus lining

Two organs involved in the menstrual cycle

Ovaries and uterus

What is changing in the ovaries in the menstrual cycle

Follicles in the ovaries grow and mature - they then release an egg (ovulation)

What is changing in the uterus

Thickness or loss of lining - the embryo needs to implant into the thick uterus lining with enough nutrients to keep it alive

Menstrual cycle days 1-4

If fertilisation and implantation does not occur then the uterus lining will shed and the egg is expelled - menstruation

Menstrual cycle days 4-14

Uterus lining thickens and blood vessels grow in preparation for the implantation of an egg

Menstrual cycle day 14

Egg is released from a follicle into the oviduct - ovulation

Menstrual cycle days 14-28

Uterus lining thickness is maintained so implantation can occur then the cycle repeats again

Name the hormones that control the menstrual cycle

FSH (follicle stimulating hormone), oestrogen, LH (luteinising hormone) and progesterone

Which two hormones are released from the pituitary gland

FSH and LH

Which two hormones are released from the ovaries

Oestrogen and progesterone

Describe role of FSH in menstrual cycle

It is secreted by the pituitary gland and transported into the bloodstream and carried to the ovaries - this binds to the receptors in the ovaries and triggers the growth of follicles, which mature into egg cells in the ovaries which releases oestrogen

Describe the role oestrogen plays in the menstrual cycle

It is secreted by the ovaries as the follicles grow and mature, it repairs and thickens the uterus lining, inhibits secretion of FSH and a high concentration of oestrogen stimulates secretion of LH from the pituitary gland

Describe the role of LH in the menstrual cycle

It is secreted by the pituitary gland and transported in the bloodstream to the ovaries where it binds to follicles and triggers one to ovulate and release an egg - a surge in LH triggers ovulation and stimulates follicle remains to develop into a corpus luteum

How does the egg move through the oviduct

The ciliated epithelial cells waft the egg along the oviduct towards the uterus

What is a corpus luteum

A temporary endocrine structure which is left after the follicle releases an egg cell - it is a mass of cells that releases progesterone and degenerates after a few days

Describe the role of progesterone in the menstrual cycle

It is secreted by the corpus luteum, and stimulates the growth of blood vessels to maintain the thickness of the uterus lining (in preparation for implantation of an egg), and it inhibits the release of FSH and LH from the pituitary gland

Why does oestrogen naturally decrease after progesterone is released

It is secreted by the maturing follicles - if FSH levels decrease from the release of progesterone then there will be fewer follicles that mature so less oestrogen will be secreted

What happens when no implantation occurs

Progesterone levels decrease and the uterus lining sheds (menstruation), causing FSH levels to increase and starting the cycle again

What happens when implantation does occur

The embryo produces its own progesterone and oestrogen which prevents further ovulation and maintains the uterus lining, making sure menstruation doesn't happen

What is menopause

The woman does not have any more follicles so cannot ovulate or menstruate any more

What are contraceptives

A method or device used to prevent pregnancy

Which hormones can be taken to prevent pregnancy

Progesterone, and progesterone combined with oestrogen

How does progesterone prevent pregnancy

Too much progesterone causes the uterus lining to thin which reduces the likelihood of egg implantation and thickens the cervical mucus - it can also prevent ovulation in some women

How does oestrogen prevent pregnancy

Oestrogen inhibits FSH production, meaning follicles will stop developing into egg cells which prevents ovulation

Outline how progesterone can be administered as a contraceptive

Mini-pill taken daily or an injection

Outline how progesterone and oestrogen combined can be administered as a contraceptive

Combined pill (taken continuously for 21 days then paused for a week) or a skin patch (worn continuously for 3 weeks then paused for a week)

Benefits of hormonal contraceptive methods

99% effective when used properly (there is no egg in the oviduct so the woman cannot get pregnant), generally lasts longer than barrier methods, and can be used to treat other conditions such as heavy periods

Risks of hormonal contraceptive methods

Side effects, do not protect against STIs, may involve uncomfortable medical procedures and are not effective if used incorrectly

Describe the barrier methods of contraception

The prevent the sperm from reaching the egg

Benefits of barrier methods of contraception

They are simple and quick to use, they prevent the spread of STIs and have no side effects

What is the main risk of barrier methods of contraception

Less effective than hormonal methods (e.g. the condom may split whilst in use)

What two hormonal methods are used to treat infertility

Clomifene therapy and IVF

Describe the role of hormones in IVF

Lots of FSH and LH are given to a woman to increase egg production and ovulation - these eggs are then retrieved from the woman's ovaries and fertilised in vitro - the resultant embryo is transferred to the woman's uterus

Outline clomifene therapy

Prescription of clomifene drug to women who do not ovulate regularly - this increases secretion of more FSH and LH which triggers more egg production and ovulation