Figure 228

Ovulation. This drawing shows a rabbit oocyte, surrounded by the cumulus oophorus, being expelled from the ruptured ovarian follicle. (Based on Weiss L, Greep RO. Histology. 4th ed. New York: McGraw-Hill, 1977.)

come closely apposed to the surface of the ovary and direct the oocyte into the uterine tube, preventing its passage into the peritoneal cavity. After ovulation, the secondary oocyte remains viable for approximately 24 hours. If fertilization does not occur during this period, the secondary oocyte degenerates as it passes through the uterine tube.

Oocytes that fail to enter the uterine tube usually degenerate in the peritoneal cavity. Occasionally, however, one may be fertilized and implant on the surface of the ovary or intestine or inside the rectouterine (Douglas) pouch. Such ectopic implantations usually do not develop beyond early fetal stages but may have to be removed surgically for the health of the mother.

Normally, only one follicle completes maturation in each cycle and ruptures to release its secondary oocyte. Rarely, oocytes are released from other follicles that have reached full maturity during the same cycle, leading to the possibility of multiple zygotes. Drugs, such as clomiphene citrate (Serophene) or human menopausal gonadotropins, which stimulate ovarian activity, greatly increase the pos-

Polycystic ovarian disease is characterized by bilaterally enlarged ovaries with numerous follicular cysts. (When associated with oligomenorrhea, scanty menstruation, the clinical term Stein-Leventhal syndrome is used.) The individual is infertile due to lack of ovulation. Morphologically, the ovaries resemble a small, white balloon filled with tightly packed marbles. Affected ovaries, often called oyster ovaries, have a smooth, pearl-white surface but do not show surface scarring, as no ovulations have occurred. The condition is due to the large number of fluid-filled follicular cysts and atrophic secondary follicles that lie beneath an unusually thick tunica albugĂ­nea. The pathogenesis is not clear but seems to be related to a defect in the regulation of androgen biosynthesis that causes production of excessive amounts of androgens that are converted to estrogens. The selection process of the follicles that undergo maturation also seems to be disturbed. The individual has an anovulatory cycle characterized by only estrogenic stimulation of the endometrium because of the inhibition of progesterone production. Progesterone inhibition is caused by failure of the Graafian follicle to transform into a progesterone-producing corpus lu-teum. The treatment of choice is hormonal to stabilize and reconstruct the estrogen-to-progesterone ratio, but in some cases, surgical intervention is necessary. A wedge-shaped incision is made into the ovary to expose the cortex, thus allowing the ova, following hormonal treatment, to leave the ovary without physical restrictions created by the preexisting thickened tunica albugĂ­nea (Fig. 22.9).

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