The Female Reproductive System

This leaflet gives a brief overview of the female reproductive system.

The organs and structures of the female reproductive system give women the ability to produce ova (an ovum is one egg, ova means multiple eggs) to be fertilised by sperm. They also provide a place for the fetus (baby) to grow and develop. Other structures such as the breasts give the mother the ability to feed and nourish a baby after birth.

Diagram detailing the uterus and ovaries

The organs of the female reproductive system are found both internally, in the pelvis, and externally (outside the main body cavity).

The organs found inside the body include:

  • Vagina - the vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. The vagina receives the penis during sexual intercourse and is a passageway for childbirth.
  • Uterus (womb) - the uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus (or body). The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.
  • Ovaries - the ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs (ova). They also produce the main female sex hormones which are released into the bloodstream.
  • Uterine (Fallopian) tubes - these are narrow tubes that are attached to the upper part of the uterus. They serve as tunnels for the ova to travel from the ovaries to the uterus. Conception, the fertilisation of an egg by a sperm, normally occurs in the uterine tubes. The fertilised egg then moves to the uterus, where it implants into the lining of the uterine wall.
ovulation and fertilisation

The external structures of the female reproductive system include parts of the vagina, and the breasts. The labia, the clitoris and a number of glands are all parts of the vagina found externally. Together these organs are known as the vulva.

Female genitals

Its main function is to give women the ability to produce ova to be fertilised, and the space and conditions to allow a fetus to develop. In order for this to happen, the female reproductive system also has the structures necessary to allow sperm from a man to meet the ova of a woman. To do all this the female reproductive system makes its own hormones that help to control a woman's monthly cycle. These hormones cause the development and release of ova so that they can be fertilised. This process is called ovulation. They also prevent ovulation during pregnancy.

The activity of the female reproductive system is controlled by hormones released both by the brain, and the ovaries. The combination of all these hormones gives women their reproductive cycle.

MENSTRUAL CYCLE DIAGRAM

The length of the reproductive (or menstrual) cycle is usually between 24-35 days. During this time an ova is developed and matured, and the lining of the uterus is prepared to receive a fertilised egg. If a fertilised egg is not implanted into the uterus, the lining of the uterus is shed and is expelled from the body. This is the bleeding known as menstruation (period). Traditionally, the first day of bleeding is known as day one of the reproductive cycle. The key event in the cycle is ovulation, the release of a mature ovum (egg) from the ovaries. This usually takes place around the 14th day of a 28-day cycle. The first part of the cycle is concerned with developing an ovum. What happens in the second part of the cycle depends on whether the ovum is fertilised.

There are five main hormones that control the reproductive cycle. Three are produced in the brain, while the other two are made in the ovaries.

  • Gonadotrophin-releasing hormone (GnRH) is made by a part of the brain called the hypothalamus. GnRH travels to another part of the brain where it controls the release of follicle-stimulating hormone (FSH) and luteinising hormone (LH).
  • FSH is released by a part of the brain called the anterior pituitary. FSH is carried by the bloodstream to the ovaries. Here it stimulates the immature ova to start growing.
  • LH is also released by the anterior pituitary and travels to the ovaries. LH triggers ovulation and encourages the formation of a special group of cells called the corpus luteum.
  • Oestrogen is produced by the growing ova and by the corpus luteum. In moderate amounts oestrogen helps to control the levels of GnRH, FSH and LH. This helps to prevent the development of too many ova. Oestrogen also helps to develop and maintain many of the female reproductive structures.
  • Progesterone is mainly released by the corpus luteum. It works with oestrogen to prepare the lining of the uterus for the implantation of a fertilised ovum. It also helps to prepare the breasts for releasing milk. High levels of progesterone control the levels of GnRH, FSH and LH.

During the last few days of the cycle, around 20 small immature ova begin to develop in the ovaries. This continues throughout the menstrual cycle. FSH and LH encourage the growth of these ova. As they grow, the ova also start to release increasing amounts of oestrogen. The amount of oestrogen produced reduces the amount of FSH released. This helps to prevent too many ova growing at the same time. Eventually one ovum outgrows the rest.

While this is happening in the ovaries, the oestrogen produced also stimulates the repair of the lining of the uterus.

The next stage in the cycle is the release of the mature ovum from the ovaries into the pelvis. By this point in the cycle, levels of oestrogen are high. Previously, medium levels of oestrogen reduced the amount of FSH and LH released. Now this high level of oestrogen is the signal for more FSH and LH to be released. LH causes the ovum to burst through the outer layer of the ovary. Usually the ovum is then swept into the uterine tubes.

Next the cells remaining when the ovum leaves the ovary become the corpus luteum. This special group of cells is capable of producing several different hormones, including progesterone and oestrogen. These hormones encourage the growth and maturation of the lining of the uterus.

What happens next depends on whether the ovum is fertilised by sperm. If the ovum is fertilised, the corpus luteum continues to produce hormones. Another hormone called human chorionic gonadotrophin (hCG) stops the corpus luteum from breaking down. The cells covering the embryo produce hCG. It is the hormone detected in pregnancy tests.

If the ovum is not fertilised, the corpus luteum can only live for a further two weeks. As it begins to break down, it releases fewer of its hormones. As the levels of progesterone and oestrogen go down, they no longer control the levels of GnRH, FSH and LH. So, these hormones increase and new ova begin to develop - the start of a new cycle. In the uterus the decrease in progesterone stimulates the release of chemicals that eventually cause the lining of the uterus to die off. This is the blood flow experienced during menstruation.

The Female Genital Organs

From Gray's Anatomy Online
Web: www.bartleby.com/107/265.html

Human Physiology/The female reproductive system

From Wikibooks, the open-content textbooks collection
Web: http://en.wikibooks.org/wiki/Human_Physiology/The_female_reproductive_system

Original Author:
Dr Rachel Hoad-Robson
Current Version:
Peer Reviewer:
Hilary Cole
Last Checked:
16/10/2012
Document ID:
12464 (v3)
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