GCSE biology: Puberty, menstrual cycle, fertility control, contraception, IVF

Hormone systems - menstrual cycle - controlling fertility - use of hormones - methods of contraception - IVF fertility treatments

Doc Brown's Biology Revision Notes

Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent

 This page will answer many questions e.g.

 What are hormones?

 How does the menstrual cycle work?

 How does In Vitro Fertilisation' (IVF) work?

 How can hormones be used to control fertility?

 What are FSH and LH hormones and what do they do?


See also Hormone system - Introduction to the endocrine system  gcse biology revision notes

For plants see Hormone control of plant growth and uses of plant hormones  gcse biology revision notes



A brief introduction to hormones (see also endocrine system for other notes and links)

Hormones are produced by and excreted from endocrine glands and are transported by the blood to their target organs

Know and understand that many process within the body are coordinated and controlled by chemical substances called hormones.

Hormones, being directly released into the blood, are quite rapidly carried to all parts of the body BUT only affect the function of particular cells.

Hormones effectively act as 'chemical messages' to trigger particular biochemical reactions.

Their effects are relatively long-lasting compared to e.g. the nerve impulses and responses of reflex arc,

but both the nervous system and hormones also help us to control conditions inside our bodies.

Know that hormones are used in some forms of contraception and in fertility treatments.

The pituitary gland produces the hormones FSH and LH which are important control chemicals in the female menstrual cycle.


Puberty and the female menstrual Cycle

Sexual reproduction cannot happen without the intervention several sex hormones.

When your body reaches puberty it starts to release sex hormones that trigger the formation of secondary sexual characteristics - exemplified by the obvious physical changes to the male and female bodies!

e.g. in men, facial hair develops. The principal reproductive male sex hormone is testosterone, produced in the testes and also stimulates sperm production and is important for the development of the male reproductive system.

In women, breasts develop. The principal reproductive sex hormone is oestrogen, produced in the ovaries. Apart from promoting physical changes e.g. breast development, oestrogen is also involved with other hormones in the menstrual cycle concerning female fertility (described next, starting with the summary diagram below).

Please note that the hormone level graphs are NOT to scale, but the timing of the peaks is important in the menstrual cycle

A simplified description of four stages in the 28 day menstrual cycle

Stage 1 - the menstruation starts - the bleeding starts on day 1 as the uterus lining breaks down for 4 days promoted by the decrease in progesterone level.

The lining of the uterus wall is called endometrium.

Stage 2 - over days 5 to 14 the uterus lining builds up again ('repaired') to give a thickish spongy layer of tissue full of blood vessels, ready to receive a fertilised egg for implantation - this is promoted by the rise in oestrogen level.

Stage 3 - around day 14 an egg is developed and released from an ovary follicle in the process called ovulation - this is facilitated by the increase in the FSH and LH hormone - they peak at ~day 13, and the egg is released at ~day 14, hardly a coincidence!

Ovulation is the release of a mature egg from an ovary follicle which typically happens once during each menstrual cycle ~day 14 in the cycle. The egg cell lives for up to 24 hours after being released, if the egg cell is not fertilised, the egg cell dies and the menstrual cycle progresses to the next phase

Ovarian follicles are small sacs filled with fluid and an immature egg, that are found inside a woman’s ovaries. They secrete hormones which influence stages of the menstrual cycle and when women begin puberty. Each has the potential to release an egg for fertilisation. Follicles and their size and status are a vital part of assessing fertility and fertility treatment (see later section on treating infertility).

Stage 4 - the thickened uterus tissue wall lasts for around 14 days. The uterus wall is maintained by the presence of increased levels of progesterone. If no fertilised egg settles on the uterus wall by day 28, the spongy uterus lining breaks up and the whole cycle repeats itself.

 

Hormonal control of the menstrual cycle (link in with stages 1 to 4 on the menstrual cycle diagram above)

Several sex hormones are involved in the menstrual cycle of a woman and hormones are involved in promoting the release of an egg: The monthly release of an egg from a woman’s ovaries and the changes in the thickness of the lining of her womb are controlled by hormones secreted by the pituitary gland and by the ovaries. You now need to know, as described below, the function of various hormones that control the different stages of the menstrual cycle.

(a) The ovaries produce the hormone oestrogen, which causes the lining of the uterus to grow and thicken. It also triggers the release of LH (luteinising hormone), which causes the release of an egg, and inhibits further release of FSH (follicle-stimulating hormone) so that only one egg is released in each cycle.

Note that the level of oestrogen rises to a peak through Stage 2, stimulating the growth and completion of the spongy uterus lining.

(b) The follicle stimulating hormone (FSH) is secreted by the pituitary gland (in the brain) and causes an egg to mature in one of the ovaries in a structure called a follicle. It also stimulates the ovaries to produce hormones including oestrogen,

Note that the level of FSH rises to a peak ~day13-14 in Stage 3 when the spongy uterus lining is complete and ready for an egg delivery.

(c) The luteinising hormone (LH), is also secreted from the pituitary gland, and stimulates the release of an egg from the ovary around day 14 in the cycle (Stage 3 ovulation).

LH causes the follicle to rupture and an egg is released.

LH also indirectly stimulates progesterone production.

LH further stimulates the remains of the follicle to develop into a structure called a corpus luteum, which secretes progesterone which maintains the physical integrity of the uterus lining.

Note that the level of LH also rises to a peak ~day13-14 in Stage 3 when the uterus lining is complete and so an egg release is stimulated.

(d) Progesterone is produced in the ovaries by the remains of the follicle after ovulation (its level peaks in the middle of Stage 4). Progesterone maintains the lining of the uterus wall in the 2nd half of the cycle (see diagram) and when its level falls, the uterus lining breaks down. It also inhibits the release of LH and FSH (described above).

Note that the level of progesterone rises to a peak in Stage 4 to maintain the spongy uterus lining in case a fertilised egg settles on it, as well as inhibiting the secretion of LH and FSH so that the cycle can be completed.

If pregnancy occurs, the progesterone level stays high to maintain the uterus lining.

As the progesterone level falls, the lining of the uterus begins to break down as the menstrual cycle repeats itself and it is a low progesterone level that allows the FSH hormone level to rise.

 

Pregnancy

If a fertilised egg lands on the uterus lining and becomes implanted, the woman becomes pregnant.

Also, the level of progesterone stays at a high level to maintain the lining of the uterus during pregnancy.


Using hormones to control fertility

Pregnancy can occur if a sperm reaches an ovulated egg.

The idea of contraception is to prevent this happening by one means or another.

Know and understand about the uses of hormones in controlling fertility.

 

Oral contraceptives

You can take oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature. noting that .

Oestrogen is used to prevent the release on an egg and the basis of one method of contraception.

Under normal circumstances in the menstrual cycle, oestrogen stimulates the release of an egg, BUT, if taken every day, keeping this hormone level high, inhibits the production of FSH and after some time both egg development and egg release are permanently stopped (as long as oestrogen continues to be taken).

Progesterone also reduces fertility by stimulating the production of thick cervical mucous, preventing sperm getting through the entrance to the uterus (the cervix) to reach an egg.

Progesterone also

(i) thins the lining of the uterus reducing the chances of a fertilised egg being implanted,

and (ii) prevents ovulation by inhibiting the production of FSH and LH (this doesn't apply to some types of mini-pill).

Oral contraceptives eg 'the pill' may contain BOTH oestrogen and progesterone to inhibit egg maturation ie prevent egg release, high and sustained levels of oestrogen inhibit FSH production and egg development is stopped permanently as long as the contraceptive is taken.

This 'pill' is sometimes referred to as the 'combined oral contraceptive pill'.

It is taken as a cycle of 21 days of taking the pill daily, followed by no pill for 7 days.

This contraception method is over 99% effective in preventing pregnancy.

However, there are side effects e.g. headaches, nausea and it doesn't protect women from sexually transmitted diseases.

In the first birth-control pills contained too large amounts of oestrogen which resulted in some women suffering significant side effects eg headaches, nausea, irregular bleeding, fluid retention and blood clots.

Birth-control pills now contain a much lower dose of oestrogen, or only contain the hormone progesterone.

Progesterone-only pills (e.g. the mini-pill oral contraceptive) lead to fewer side effects and can be as effective as oestrogen pills. The mini-pill must be taken every day.

 

Other hormone contraception treatments

(a) The contraceptive patch contains oestrogen and progesterone (same as combined pill). It is usually 5 cm x 5 cm and is stuck on the skin and is 91-99% effective.

Typically, the patch is worn on the skin in a 4 week cycle - its replaced once a week for 3 weeks and then no patch for 1 week.

(b) A contraceptive implant is inserted under the skin and releases a continuous dose of progesterone. This stops the ovaries releasing an egg, it thickens the cervix mucous, so hindering the sperm swimming to the egg and so stops the implantation of a fertilised egg in the uterus. A contraceptive implant can last for three years and is 99% effective.

(c) A contraceptive injection of only progesterone can have a effect for 2-3 months.

A few general comments on these hormonal methods of contraception (a) to (c)

Advantages:

Convenience - you don't have to remember to take the pill every day, but you must remember to change the patch or implant or receive the next injection when appropriate.

High percentage of effectiveness in preventing pregnancy.

Disadvantages - mainly side effects:

With any hormonal contraceptive treatment you may get temporary side effects at first, including headaches, nausea, breast tenderness, mood changes, heavy and irregular periods.

The patch may cause skin irritation.

(d) An intrauterine device (IUD) is a T-shaped device that is inserted into the uterus to kill sperm which prevents the implanting of a fertilised egg.

There are two main types of IUD (sometimes called an intrauterine system (IUS)..

(i) Plastic IUDs releasing progesterone (hormonal method as above and can be effective for 3-5 years).

(ii) Copper IUDs that kill sperm and prevent them surviving in the uterus, and so can never fertilise a released egg (non-hormonal method, see more in next section on other methods of non-hormonal contraception).

 


Non-hormonal methods of preventing pregnancy

 

Barrier methods to stop the sperm ever meeting an egg, hence stop fertilisation of egg and therefore no pregnancy.

All such devices must be carefully fitted in place before sexual intercourse takes place.

(i) Condoms are worn over the penis during intercourse to stop sperm entering the vagina. Female condoms are worn inside the vagina.

Note that condoms are the only form of contraception that protect you against sexually transmitted diseases.

(ii) A diaphragm is a shallow flexible plastic cup or dome shaped device that fits over the opening of cervix making a barrier to the entrance to the uterus. The diaphragm prevents sperm reaching an egg and it can be used in conjunction with a spermicide that kills sperm.

 

Killing the sperm

(i) It is possible to use a spermicide on its own as a contraceptive, but is only 70-80% effective, much less than the other contraception methods previously described.

(ii) Copper IUDs that kill sperm and prevent them surviving in the uterus, and so can never fertilise a released egg (non-hormonal method.

 

Sterilisation - requires a surgical procedure

This involves cutting or tying tubes in the reproductive system ...

(i) female - the fallopian tubes which connect the ovaries to the uterus, eggs cannot be released into the uterus,

(ii) male - the sperm duct tube that connects the testes with the penis, sperm cannot be injected into the vagina.

These are surgical procedures with a permanent effect -there is only a very small chance of the tubes joining up again.

 

'Natural' methods and the menstrual cycle

This involves knowing when the woman is most fertile within the 28 day menstrual cycle.

Therefore the idea is to avoid sexual intercourse during these fertile periods.

However, it is not very effective, but it is used by people who think that barrier and hormonal methods are unnatural (or considered wrong by some religious teachings).

The man can also remove his penis before ejaculation to prevent sperm entering the uterus, but that requires a good deal of self control.

 

Abstinence

No sexual intercourse at all, is the only truly 100% guaranteed pregnancy prevention.

 

Comparing barrier, natural and hormonal methods of contraception

Generally speaking, if used correctly, hormonal methods are more effective at preventing pregnancy and have the advantage of not having to think about contraception each time a couple have sex.

However, hormonal contraception methods can have unpleasant side effects such as nausea, headaches, ane, mood changes.

AND, unlike the use of condoms, hormonal methods do NOT protect against sexually transmitted diseases.

In using barrier and natural methods things must be done carefully. Condoms can split, natural cycles can be 'mistimed'. BUT in this sense its no different using hormonal methods of contraception - you still have to the pill or replace the patch at the right times.

Long-lasting methods of contraception lasting for weeks, months or years might be preferable than short-term methods, if only for convenience and less thinking to do.

You should get, and take, good medical advice from practitioners e.g. doctor or nurse.


Methods of increasing fertility

This is the complete opposite of contraception.

The desire for children is a very powerful motivation in human nature but to be infertile means you cannot reproduce naturally.

Unfortunately some women are infertile, but, help is at hand from various hormonal treatments to greatly improve their fertility and ultimately deliver a baby.

Using hormones to increase fertility

Some women have too low a level of FSH (follicle-stimulating hormone) to stimulate the eggs to mature in the ovary. Therefore no ovulation, no eggs are released and pregnancy cannot happen.

FSH and LH (luteinising hormone) can be administered as a fertility drug to stimulate ovulation.

The method obviously improves fertility - the chances of getting pregnant, but there are 'negatives'.

(i) The treatment is expensive and doesn't always work.

(ii) Sometimes too many eggs are stimulated at the same time resulting in multiple pregnancies e.g. twins or triplets.

Women can be infertile due to lack of ovulation (none or irregular ovulation), so another similar approach is to use the medication clomifene (clomiphene).

Clomifene works by causing more FSH and LH to be released by the body - this in turn stimulates eggs to mature and be released (ovulation).

If you know when the woman is more likely to ovulating, a couple can have intercourse during the treatment period to increase the chances of the woman becoming pregnant.

However, there are some unpleasant side effects from using clomifene e.g. pelvic pain and hot flushes.

 

IVF treatment - In Vitro Fertilisation

Why choice of IVF?

Sometimes giving FSH and LH in a ‘fertility drug’ to a woman whose own level of FSH is too low to stimulate eggs to mature doesn't always work.

If women are unable to get pregnant with hormonal treatment they may try 'In Vitro Fertilisation' (IVF) treatment.

IVF is an example of Assisted Reproductive Technology (ART), defined as a fertility treatment involving the handling of eggs (usually fertilised) outside of the body.

The IVF procedure

IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs where they would not have been released - this must be done before egg collection, and it also means more than one egg can be collected.

In IVF treatment, after the potential mother has been treated with FSH and LH, eggs are collected from her ovaries and fertilised in the laboratory by sperm from the father.

IVF treatment can also involve a technique called Intra-Cytoplasmic Sperm Injection (ICSI), where the sperm is directly injected into an egg.

This may be applied if the sperm count of the man is low.

In either case, in a laboratory, the fertilised eggs grow and develop into embryos in a incubator.

At the stage when the fertilised eggs are just tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb) to attempt a pregnancy.

 

Advantages and disadvantages of IVF treatment - the 'pros and cons'

IVF has enabled many mothers to get pregnant and give birth to healthy children - a wonderful application of medical science and technology.

BUT it doesn't always work for an infertile couple and there other downsides too.

It is possible for several eggs to be simultaneously matured resulting in multiple pregnancies eg twins, triplets and more develop from the growth of more than one embryo into a baby!

This increases the risk for mother and babies - multiple pregnancy puts extra strain on the mother - there is an increased risk of an unsuccessful birth e.g. miscarriage or stillbirth.

IVF has a low success rate, averaging 26% in the UK. It ranges from 29% for women under 35, down to 23% or less for women over 35. Age is an important factor and fertility decreases as a woman gets older.

This low success rate makes the whole process very stressful both physically and mentally - the situation is emotionally draining, especially if IVF treatment fails several times.

Women can suffer side-effects from the hormone treatment which can be physically and emotionally demanding e.g. abdominal pain, dehydration, vomiting - an overlap of side effect symptoms from hormonal contraception

BUT, most infertile couples would regard IVF treatment is worth the risk.

Advances in IVF techniques

Microscope techniques have become more advanced and improved the success rate of IVF fertility treatment.

This involves using special micro-tools to manipulate sperm and eggs under the microscope.

You can now remove single cells from the embryo for genetic testing to check if the genome will facilitate a healthy embryo-baby.

With a microscope and camera, you can also use time lapse imaging of the embryo growing in the incubator, allowing you to continuously monitor the growth of the embryos to see which are the most likely to result in a successful pregnancy

 

Objections to IVF treatments

Most objections centre around the ethical issues of IVF.

(i) IVF procedures often result in unused embryos being destroyed and some people consider this unethical - immoral, because you have destroyed a potential human life.

(ii) The genetics and genetic testing of embryos before implantation in the mother's womb raises the ethical issue of preferential choice of characteristics of the baby e.g. choice of gender, eye colour or even whether you allow a child to be born with disabilities.

 

Evaluation of IVF

You might be expected to evaluate the benefits of, and the problems that may arise from, the use of hormones to control fertility, including In Vitro Fertilisation (IVF) and might be given information data to work on.


See also Hormone system - Introduction to the endocrine system  gcse biology revision notes

For plants see Hormone control of plant growth and uses of plant hormones  gcse biology revision notes


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