Hormones

Hormones play an important role in every woman's life. They influence all aspects of life from puberty, pregnancy and birth to the menopause, as well as influencing emotions and mood. Hormones can be linked to pre-menstrual syndrome and depression, and disorders of the female hormones can cause fertility problems as well as other medical conditions.

What are hormones?

Hormones are messengers which co-ordinate many functions in the body, including growth, the menstrual cycle (periods) and metabolism. Female hormones include: Oestrogen, Progesterone, Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH). They all work in a cyclical pattern to regulate the menstrual cycle. These hormones also play a large role in pregnancy and birth.

What do they do?

Oestrogen is mainly produced by the ovaries and regulated by the pituitary gland in the brain. Oestrogen is protective to the heart and bones and is involved in keeping the reproductive organs healthy. In the menstrual cycle oestrogen causes eggs to mature and thickens the lining of the womb. In pregnancy the levels increase and after pregnancy levels fall sharply back down to normal and this change is thought to be involved in causing post-natal depression. As women get older the function of the ovaries diminish, lowering the levels of oestrogen causing periods to become irregular and stop and this is called the menopause.

Progesterone is produced in the ovaries but also by the placenta during pregnancy. In the menstrual cycle progesterone thickens the womb lining to prepare for implantation of an embryo (fertilized egg). In pregnancy progesterone levels increase, helping to maintain pregnancy and after pregnancy levels fall sharply back down to normal and this change, along with the drop in oestrogen levels is thought to be a factor in the cause of the most severe form of post-natal depression. After menopause progesterone levels also decrease significantly.

Gonadotrophin Releasing Hormone (GnRH) is produced and released by the hypothalamus. During the menstrual cycle GnRH stimulates the release of follicle stimulating hormone (FSH) every month. 

Follicle Stimulating Hormone (FSH) is produced and released by the pituitary gland. In the menstrual cycle FSH stimulates the ovaries to grow one or more follicles and ripen the egg within them. FSH also stimulates the ovaries to produce oestrogen.

Luteinising Hormone (LH) is produced in the pituitary gland. A surge of this hormone during the middle of the menstrual cycle triggers ovulation (release of a ripened egg).

HCG- (Human Chorionic Gonadotrophin) is produced by the developing placenta in pregnancy. Pregnancy tests work by detecting and measuring  HCG levels in the urine, (or blood).

 

How do hormones work together in the menstrual cycle?

The process starts in the brain with the hypothalamus producing GnRH. It travels to the pituitary gland and signals it to release follicle-stimulating hormone (FSH). FSH stimulates the ovaries to start ripening eggs in follicles, only one of which usually reaches maturity and stimulates the ovaries to produce oestrogen. As the egg ripens the lining of the womb starts to thicken in readiness to support a pregnancy.

As oestrogen levels rise, FSH levels fall temporarily and then rise again, accompanied by a surge in luteinising hormone (LH) from the pituitary gland. This triggers the most mature egg to burst out of its sac or follicle, away from the ovary and into the fallopian tube (ovulation) usually around day 14 of the cycle.

Just before ovulation, oestrogen changes the mucus in the cervix so that it becomes thin, clear and stretchy allowing sperm to penetrate into the womb and travel up to the fallopian tubes where fertilisation might take place.

In the ovary, the now empty follicle or sac collapses and becomes a corpus luteum, some of the supporting cells becoming the cells which produce progesterone. Progesterone changes the mucus in the cervix so that it becomes impenetrable to sperm and acts on the lining of the uterus to become thick and spongy to receive a fertilised egg.

If fertilisation occurs the pregnancy will embed in the lining of the uterus and progesterone levels rise. If the egg isn’t fertilised, progesterone levels fall triggering the lining of the womb to shed with bleeding, (the menstrual period).

Potential problems

Hormones have a continuous influence on women throughout their lives and when imbalances or oversensitivity occur this can potential difficulties. Hormonal fluctuations are thought to be important in premenstrual syndrome (pms), period problems, fertility problems, polycystic ovarian syndrome and depression. Hormonal changes during the menopause  result in various symptoms,  which can be distressing and unpleasant for some women.

 

Page last updated January 2013

 

 

 

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