C Fallopian Tubes

(1) Location. Each tube is about 4 inches long and extends medially from each ovary to empty into the superior region of the uterus.

(2) Function. The fallopian tubes transport ovum from the ovaries to the uterus. There is no contact of fallopian tubes with the ovaries.

(3) Description. The distal end of each fallopian tube is expanded and has finger-like projections called fimbriae, which partially surround each ovary. When an oocyte is expelled from the ovary, fimbriae create fluid currents that act to carry the oocyte into the fallopian tube. Oocyte is carried toward the uterus by combination of tube peristalsis and cilia, which propel the oocyte forward. The most desirable place for fertilization is the fallopian tube.

Oogenesis Animation
Figure 1-4. Human ovary.

(1) Functions. The ovaries are for oogenesis-the production of eggs (female sex cells) and for hormone production (estrogen and progesterone).

(2) Location and gross anatomy. The ovaries are about the size and shape of almonds. They lie against the lateral walls of the pelvis, one on each side. They are enclosed and held in place by the broad ligament. There are compact like tissues on the ovaries, which are called ovarian follicles. The follicles are tiny sac-like structures that consist of an immature egg surrounded by one or more layers of follicle cells. As the developing egg begins to ripen or mature, follicle enlarges and develops a fluid filled central region. When the egg is matured, it is called a graafian follicle, and is ready to be ejected from the ovary.

(3) Process of egg production--oogenesis (see figure 1-5).

(a) The total supply of eggs that a female can release has been determined by the time she is born. The eggs are referred to as "oogonia" in the developing fetus. At the time the female is born, oogonia have divided into primary oocytes, which contain 46 chromosomes and are surrounded by a layer of follicle cells.

(b) Primary oocytes remain in the state of suspended animation through childhood until the female reaches puberty (ages 10 to 14 years). At puberty, the anterior pituitary gland secretes follicle-stimulating hormone (FSH), which stimulates a small number of primary follicles to mature each month.

Anterior Pituitary Gland Process
Figure 1-5. The process of oogenesis.

(c) As a primary oocyte begins dividing, two different cells are produced, each containing 23 unpaired chromosomes. One of the cells is called a secondary oocyte and the other is called the first polar body. The secondary oocyte is the larger cell and is capable of being fertilized. The first polar body is very small, is nonfunctional, and incapable of being fertilized.

(d) By the time follicles have matured to the graafian follicle stage, they contain secondary oocytes and can be seen bulging from the surface of the ovary. Follicle development to this stage takes about 14 days. Ovulation (ejection of the mature egg from the ovary) occurs at this 14-day point in response to the luteinizing hormone (LH), which is released by the anterior pituitary gland.

(e) The follicle at the proper stage of maturity when the LH is secreted will rupture and release its oocyte into the peritoneal cavity. The motion of the fimbriae draws the oocyte into the fallopian tube. The luteinizing hormone also causes the ruptured follicle to change into a granular structure called corpus luteum, which secretes estrogen and progesterone.

(f) If the secondary oocyte is penetrated by a sperm, a secondary division occurs that produces another polar body and an ovum, which combines its 23

chromosomes with those of the sperm to form the fertilized egg, which contains 46 chromosomes.

(4) Process of hormone production by the ovaries.

(a) Estrogen is produced by the follicle cells, which are responsible for secondary sex characteristics and for the maintenance of these traits. These secondary sex characteristics include the enlargement of fallopian tubes, uterus, vagina, and external genitals; breast development; increased deposits of fat in hips and breasts; widening of the pelvis; and onset of menses or menstrual cycle.

(b) Progesterone is produced by the corpus luteum in presence of LH in the blood. It works with estrogen to produce a normal menstrual cycle. Progesterone is important during pregnancy and in preparing the breasts for milk production.

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  • kevin
    How to stimulate anterior pituitary?
    7 years ago

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