A woman has two ovaries. There function is to release egg cells and to produce hormones. They usually produce one egg per month. Their hormonal function is unique. The normal ovary produces two very important hormones but in a very special unique way. For the first half of the menstrual cycle only Estrogen is produce but in the latter half the ovary also starts producing another hormone Progesterone. Refer to normal menstruation to see the effect of these hormones on the endometrium. The ovary also produces small amounts of testosterone ( the so called male sex hormone).
When a baby girl is born , her ovaries contain all the egg cells (ova) she will ever possess. The egg cells are formed during intra uterine life and no new egg cells are formed after birth. This differs completely from the male, who starts producing sperms only at puberty and than continues to produce sperms for the rest of his life. This is why women enter the menopause when ALL THEIR EGG CELLS ARE USED UP.
The following illustrated discussion will show how egg cells are released and will also be the basis for a discussion on ovarian cysts.
This graphic presentation will illustrate the process of ovulation and the changes that occur in the ovaries during the monthly female cycle.
A Graphic Presentation Of Ovulation
This drawing is to help you to orientate and understand the next drawings. The area in the square is enlarged in the next drawings. The ovary is viewed in a cross section ( the ovary is cut in half and we are looking at the cut side)
This illustrates the resting ovary. The ova (egg cells) are visible. There are about 5 hundred thousand of them in each ovary at birth.
The structure to the right marked Fallopian tube, is the funnel shaped opening of the Fallopian tube. The released egg cell will be sucked into the Fallopian tube (see later). The primary follicle (the structure containing the egg cell) consists of the egg cell surrounded by a layer of cells.
At puberty, one of these egg cells will start to ripen and will be released a couple of weeks later.
The early development of the egg cell is illustrated. Water starts accumulating around the egg cell and a small blister like structure is formed. It is called a follicle. It gradually increases in size as more water accumulates. The accumulating water is colored blue.
The follicle is continuously increasing its size and is now clearly visible and much larger.
Note that the egg is also moved from it's central position to the surface of the ovary.
The follicle is now approximately 20-25 mm in diameter and bulging out of the ovary. It is now approximately 2 weeks after the onset of the previous menstruation.
The follicle ruptures and the egg cell is released. The egg cell is now ready to be fertilized. It is slowly sucked into the Fallopian tube. ( See Fertilization) The rupture and releasing of the egg cell is referred to as"OVULATION". Fertilization can only take place after ovulation.
A very important change is taking place in the ovary. A new structure is developing from the remains of the follicle which released the egg cell. This new structure is called a CORPUS LUTEUM (Latin meaning yellow body). The corpus luteum is the only structure which produces the hormone progesterone in significant quantities.
The cells that form the lining of the follicle, proliferate (multiply and become many), develop a yellowish color and produce progesterone and estrogen. There is usually a small amount of blood present in the center of the corpus luteum. (in the cavity of the previous follicle).
The corpus luteum increases in size. Progesterone and estrogen production continues. The effect of progesterone on the endometrium prepare the endometrium for pregnancy. ( see Implantation and Normal menstruation )
If pregnancy does not occur, the corpus luteum dies and all that remains is scar tissue called a corpus albicans. The ovary ceases to produce hormones (estrogen and progesterone) and menstruation starts.
The corpus luteum is a unique structure. All other hormonal glands function under the control of your body, except the corpus luteum . It secretes estrogen and progesterone completely independent from any control system and dies after ten days unless a pregnancy occurs. (This is not 100 % true, it needs the hormone LH to develop and the hormone hCG keeps it functioning during early pregnancy.) (See Control systems and Pituitary and Early Pregnancy)and Pregnancy and Childbirth.