Hormones in human reproduction

In a nutshell

Hormones are required for the development of secondary sexual characteristics. Testosterone is an important male sex hormone. Progesterone, oestrogen, follicle-stimulating hormone and luteinising hormone are important female sex hormones that control the menstrual cycle. It is possible to prevent pregnancy using hormonal and non-hormonal methods of contraception.

Hormones and puberty

At puberty, your body starts releasing sex hormones. These sex hormones trigger the development of secondary sexual characteristics.

Example

Facial hair in males and breasts in females.

Female sex hormones also cause eggs to mature and develop. In females, the main reproductive hormone is oestrogen, it is produced by the ovaries and is involved in the menstrual cycle. In males, the main reproductive hormone is testosterone. It is produced by the testes and stimulates the production of sperm.

Sex hormones

Hormone	Role
Testosterone	Stimulates sperm production and is important for the development of the male reproductive system.
Oestrogen	It is involved in the menstrual cycle and promotes female sexual characteristics (such as breast development).
Progesterone	Produced by the ovaries and helps support pregnancy and is involved in the menstrual cycle.
Follicle-stimulating hormone (FSH) and Luteinising hormone (LH)	Both of these hormones are released by the pituitary gland and help control the menstrual cycle.

The menstrual cycle

The menstrual cycle is the process where the female body prepares the uterus in case it receives a fertilised egg. If an egg is not fertilised, the uterus lining will shed and cause bleeding from the vagina. The menstrual cycle lasts for approximately $28\ days$ .

The menstrual cycle occurs in four stages:

Biology; Animal coordination, control and homeostasis; KS4 Year 10; Hormones in human reproduction

Stage	Event	Day
1.	Bleeding from the vagina begins as the uterus lining is shed, this is called menstruation or having a period.	$1$
2.	The blood loss stops and the uterus lining begins to build up again. An egg starts to mature in an ovary.	$4-14$
3.	A mature egg is released from the ovary, it travels through the oviduct into the uterus. This is known as ovulation.	$14$
4.	The uterus wall is thick as it waits for a fertilised egg, if the egg is not fertilised the spongy lining will shed and the whole cycle starts again.	$14-28$

The menstrual cycle and hormones

The menstrual cycle is controlled by four hormones:

FSH (Yellow)

FSH is released by the pituitary gland. It causes a follicle, which is an egg surrounded by its cells, to mature in one of the ovaries. This stimulates the production of oestrogen.

Oestrogen (Blue)

Oestrogen is released by the ovaries. It causes the lining of the uterus to thicken and grow. A high level of oestrogen stimulates a rapid increase in LH.

LH (Brown)

LH is released by the pituitary gland. An increase in LH stimulates ovulation at day $14$ , this causes the follicle to rupture and an egg to be released. The remains of the follicle are stimulated by LH to form a structure known as corpus luteum, which secretes progesterone.

Progesterone (Green)

This is released by the corpus luteum after ovulation. Its role is to maintain the lining of the uterus and inhibit the release of FSH and LH. When the level of progesterone decreases and there is a low level of oestrogen, the uterus lining breaks down. Low progesterone allows FSH to increase and the whole cycle starts again. If a fertilised egg implants in the uterus, the level of progesterone will stay high to maintain the uterus lining during pregnancy.

Biology; Animal coordination, control and homeostasis; KS4 Year 10; Hormones in human reproduction

Hormonal methods of contraception

When a sperm reaches an egg, a pregnancy can occur. Contraception tries to prevent pregnancy from happening. Hormones can be used to reduce fertility. These are known as hormonal contraceptives.

Oral contraceptives containing hormones

These are taken orally, through the mouth, as pills by females. They stop FSH from being released, which stops eggs from maturing. Oral contraceptives are over $99\%$ effective at preventing pregnancy. However, they can have bad side effects such as headaches, weight gain and nausea.

Progesterone contraceptives

These contraceptives work by slowly releasing progesterone, this stops the egg from maturing or being released from the ovaries.

Examples

Method	Explanation
*Contraceptive patch*	This is a small patch that is stuck to the skin and lasts one week. It also releases oestrogen.
*Contraceptive implant*	This is inserted under the skin of the arm and lasts for up to $3\ years$ .
*Contraceptive injection*	This is an injection of progesterone that lasts $2-3\ months$ .

Intrauterine devices

An intrauterine device (or IUD) is a T-shaped device that is inserted directly into the uterus. It can stop fertilised eggs from implanting in the uterus wall. Some types of IUD release a hormone.

Non-hormonal methods of contraception

There are other methods to prevent pregnancy that do not use hormones. Non-hormonal contraceptives stop the sperm from getting to the egg.

Barrier methods

Method	Explanation
Condom	Condoms are worn over the penis during sexual intercourse. They also protect against sexually transmitted infections (STIs).
Female condom	Female condoms are worn inside the vagina. They can protect against STIs.
Spermicide	Spermicide is a chemical that disables or kills sperm. It can be used alone but is only $70-80\%$ effective.
Diaphragm and spermicide	A diaphragm is a shallow plastic cup that fits over the entrance to the uterus. It has to be used with spermicide.

Other ways to avoid pregnancy

Sterilisation

In females, sterilisation involves cutting or tying the oviducts. In males, it involves cutting or tying the sperm ducts. Sterilisation is permanent.

Natural methods

Pregnancy may be avoided by not having sexual intercourse when a woman is at the stage of the menstrual cycle when she is most likely to get pregnant. It is not a very effective method.

Abstinence

The only way to $100\%$ prevent a sperm and an egg from fusing is for males and females to avoid sexual intercourse.