Human Reproduction

Puberty

Puberty is the gradual change of a persons body as they enter adulthood and will develop secondary sexual characteristics. Puberty generally takes place between the ages of 10 and 16 and is controlled by hormones.

In males, testosterone starts to be produced in the testes and produces secondary sexual characteristics such as the development of sexual organs, growth of facial, pubic and underarm hair and voice breaks as their voice gets deeper. During puberty men will also start producing sperm in their testes.

In females, oestrogen starts to be produced in the ovaries and produces secondary sexual characteristics such as the development of breasts and sexual organs, growth of pubic and underarm hair and the widening of hips. During puberty women will also start releasing eggs from their ovaries and their menstrual cycle will begin.

Menstrual Cycle

The menstrual cycle is the system where the female body prepares for potential pregnancy by building up the lining of the uterus and developing and releasing an egg cell from the ovaries. If no fertilised egg lands on the uterus wall after 28 days, the lining breaks down again and the cycle repeats.

Day 1: Menstruation– the uterus lining is broken down if there is no fertilised egg, causing bleeding.

Day 4: The lining of the uterus begins to build back up in preparation for a fertilised egg.

Day 14: Ovulation –  an egg is released from the ovary and travels down the oviduct into the uterus.

Day 28: The wall is maintained for 14 days until day 28. If there is no fertilised egg on the lining of the uterus then the menstrual cycle will begin again.

The menstrual cycle is controlled by hormones:

• Follicle-stimulating hormone (FSH) is produced by the pituitary gland in the brain and causes eggs to mature in the ovaries. 
• Luteinising hormone (LH) is produced by the pituitary gland and causes the release of the egg from the ovaries (ovulation).
• Oestrogen is produced by the ovaries and causes the lining of the uterus to grow and thicken.
• Progesterone is produced in the ovaries by an empty egg follicle and maintains the lining of the uterus.

Hormone Interactions in the Menstrual Cycle

All 4 hormones interact to produce the menstrual cycle:

FSH causes an egg to mature and develop in a follicle in the ovaries then stimulates the ovaries to produce oestrogen.

Oestrogen then causes the lining of the uterus to grow, inhibits the release of FSH and stimulates the release of LH.

LH stimulates the release of the egg (ovulation) from the follicle in the ovaries.

The remains of the follicle in the ovaries produces progesterone that maintains the lining of the uterus for 14 days and inhibits FSH and LH. When progesterone levels start to decrease, uterus lining breaks down and FSH and LH are no longer inhibited so the cycle can start again. 

Reducing fertility

Pregnancies occur when an egg, released during the menstrual cycle, is fertilised by a sperm. Pregnancies can be prevented and avoided by reducing fertility using different hormonal and non-hormonal methods of contraception.

Abstaining from intercourse is the only way to fully prevent pregnancy. Some people prefer to only abstain from intercourse when the egg has been released so when they are most fertile. This method is much less effective.

Increasing fertility

Developments in fertility research means infertile women now have the chance to have their own children using hormone treatments or IVF.

Hormone treatments:

Women who have low FSH levels struggle to get pregnant because their eggs do not mature in the ovaries or get released. This can be treated by giving the woman a fertility drug containing FSH and LH which will stimulate ovulation. Some people spend lots of money on the treatment as not every round is successful. There is also an increased chance of twins, triplets etc. if multiple eggs are stimulated accidentally.

IVF:

If hormone treatments do not work or the issue is with the man’s fertility, couples may choose to use IVF (in vitro fertilisation).

1. Mother is given LH and FSH to stimulate the maturation and release of several eggs.
2. Eggs are collected from the mother and fertilised by sperm from the father in a laboratory. 
3. The fertilised eggs then develop into embryos (small balls of cells) and a few are implanted into the mothers uterus where they will hopefully develop into healthy babies.

IVF is a very safe way for infertile people to increase their chances of having a baby. Embryos can be screened for certain diseases and selected based on their health and any unused eggs can be used for further research. Development of certain microscopy techniques have also allowed IVF treatments to be improved greatly in recent years.

However, IVF treatments have some issues:

• The success rate is still relatively low and decreases with increasing age of the mother.
• There are side effects to the drugs used in the process.
• It can be emotionally and physically stressful, especially if rounds of IVF are unsuccessful.
• There is a greater risk of multiple births (twins, triplets etc.) which can put great risk and strain on the babies and mother.
• It is very expensive. The NHS cannot fund all requests for IVF so has to pick between cases. Some people decide to have private IVF treatment but this is not affordable for everyone.
• IVF is opposed by people who believe that embryos are potential new lives. Some unused embryos are thrown away and they believe that this is unethical. 
• Other people believe IVF may be used to select for desirable qualities in babies and will lead to designer babies.