Ovary

Production of gametes and steroid hormones are the two major functions of the ovary

The ovaries have two interrelated functions: the production of gametes (gametogenesis) and the production of steroids (steroidogenesis). In the female, the production of gametes is called oogenesis. Developing gametes are called oocytes; mature gametes are called ova.

Two major groups of steroid hormones, estrogens and progestogens, are secreted by the ovaries:

• Estrogens promote growth and maturation of internal and external sex organs and are responsible for the female sex characteristics that develop at puberty. Estrogens also act on mammary glands to promote breast development by stimulating ductal and stromal growth and accumulation of adipose tissue.

• Progestogens prepare the internal sex organs, mainly the uterus, for pregnancy by promoting secretory changes in the endometrium (discussed in the section on cyclic changes in the endometrium). Progestogens also prepare the mammary gland for lactation by promoting lobular proliferation.

Both hormones play an important role in the menstrual cycle by preparing the uterus for implantation of a fertilized ovum. If implantation does not occur, the endometrium of the uterus degenerates and menstruation follows.

• Cortex or cortical region found in the peripheral portion of the ovary surrounding the medulla. The cortex contains the ovarian follicles embedded in a richly cellular connective tissue. Scattered smooth muscle fibers are present in the stroma around the follicles. The boundary between the medulla and cortex is indistinct.

"Germinal epithelium" instead of mesothelium covers the ovary

The surface of the ovary is covered by a single layer of cuboidal and, in some parts, almost squamous cells. This cellular layer, known as the germinal epithelium, is continuous with the mesothelium that covers the mesovarium. The term germinal epithelium is a carryover from the past when it was incorrectly thought to be the site of germ cell formation during embryonic development. It is now known that the primordial germ cells (both male and female) are of ex-tragonadal origin and that they migrate from the embryonic yolk sac into the cortex of the embryonic gonad, where they differentiate and induce differentiation of the ovary. A dense connective tissue layer, the tunica albugínea, lies between the germinal epithelium and the underlying cortex.

Ovarian follicles provide the microenvironment for the developing oocyte

Ovarian follicles of various sizes, each containing a single oocyte, are distributed in the stroma of the cortex. The early primary follicle follicle approaching maturity mature Graafian follicle

oocyte corpus luteu follicle released oocyte blood vessels corpus albicans

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