Hormones in human reproduction
Hormones are secreted by glands in the endocrine system. During puberty, hormones create changes in physical and emotional characteristics.
The role of reproductive hormones in the menstrual cycle
A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of specific target organs (and is then destroyed by the liver).
Different hormones affect different organs or cells.
Puberty
Puberty is the stage in life when a child's body develops into an adult's body. The changes take place gradually, usually between the ages of 10 and 16.
During puberty, reproductive hormones cause secondary sex characteristics to develop:
- testosterone - produced by the testes – is the main male reproductive hormone and it stimulates sperm production
- oestrogen - produced by the ovaries – is the main female reproductive hormone. At puberty, eggs begin to mature and one is released approximately every 28 days. This is ovulation.
Changes during puberty
A variety of changes happen to boys and girls during puberty.
| Boys only | Boys & girls | Girls only |
|---|---|---|
| Voice breaks | Pubic hair grows | Voice deepens gradually |
| Hair grows on face and body | Underarm hair grows | Hips get wider |
| Body becomes more muscular | Sexual organs grow and develop | Breasts develop |
| Testes start to produce sperm cells | Ovaries start to release egg cells - menstruation starts |
The menstrual cycle and hormones
Greg Foot describes the interaction of FSH, LH, oestrogen and progesterone in the menstrual cycle
The menstrual cycle is a recurring process which takes around 28 days. During the process, the lining of the uterus is prepared for pregnancy. If implantation of the fertilised egg into the uterus lining does not happen, the lining is then shed. This is known as menstruation.
Several hormones control this cycle – for example, they are involved in controlling the release of an egg each month from an ovary, and changing the thickness of the uterus lining.
| Hormone | Produced | Role |
|---|---|---|
| FSH (follicle stimulating hormone) | Pituitary gland | Causes an egg to mature in an ovary. Stimulates the ovaries to release oestrogen |
| Oestrogen | Ovaries | 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. |
| LH (luteinising hormone) | Pituitary gland | Triggers ovulation (the release of a mature egg) |
| Progesterone | Ovaries | Maintains the lining of the uterus during the middle part of the menstrual cycle and during pregnancy. |
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.