Encyclopedia of Reproductive Technologies

By Annette Burfoot | Go to book overview

thirty-nine
Ovarian Suppression
by GnRH Agonists

ANDRÉ LEMAY


Egg Maturation and Female Sex Hormones

The human ovaries have two main roles: the release of an egg each month and the secretion of sex hormones responsible for the differentiation and function of the uterus and vagina. These functions are principally controlled by two hormones, FSH (follicle-stimulating hormone) and LH (luteinizing hormone). These two chemical regulators come from the pituitary gland, located at the base of the brain. At the time of the menses, FSH and LH initiate the stimulation of a cohort of eggs. The eggs are surrounded by granulosa cells that secrete the female sex hormones, the estrogens, principally estradiol. The secretion of estradiol is responsible for the proliferation of the endometrium, the tissue lining the uterine cavity. After a few days, one follicle among the cohort becomes dominant and the others regress. At ultrasonic examination it can be seen as a small cyst containing fluid, and at maturation it has an average diameter of two centimeters and protrudes from the surface of the ovary. At midcycle, a surge of LH and FSH triggers ovulation: the rupture of the follicle and the release of the egg. Following ovulation the cells of the follicle form a yellow cyst (corpus luteum) that still secretes estrogens and in addition releases large amounts of progesterone. This second type of female sex hormone is required for the maturation of the endometrium and implantation of a fertilized egg. In the absence of implantation, the corpus luteum cannot

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