Corpus luteum

The corpus luteum (Latinfor "yellow body") is a small, temporary endocrinestructure in animals. It develops from an ovarian follicleduring the luteal phaseof the estrous cycle, following the release of a mature eggfrom the follicle during ovulation. While the egg traverses the Fallopian tubeinto the uterus, the corpus luteum remains in the ovary.

Function

In the ovary, the corpus luteum secretes estrogensand progesterone, which are steroid hormonesresponsible for the thickening of the endometriumand its development and maintenance, respectively. If the egg is not fertilized, the corpus luteum stops secreting progesterone and decays (after approximately 12 days in humans). It then degenerates into a corpus albicans, which is a mass of fibrous scartissue. The uterine lining sloughs off without progesterone and is either resorbed (in most animals) or expelled through the vagina(in humans and some great apes). The latter is called menstruation.

If fertilized, however, the embryo secretes the hormone human chorionic gonadotropin(hCG) or a similar hormone in other species. This hormone signals the corpus luteum to continue progesterone secretion, thereby maintaining the thick lining (endometrium) of the uterus, and providing an area rich in blood vesselsin which the zygote(s) can develop. From this point on, the corpus luteum is called the corpus luteum graviditatis. The introduction of the hormone prostaglandinat this point causes the degeneration of the corpus luteum and the abortionof the fetus. However, in placental animals such as humans the placentaeventually takes over progesterone production and the corpus luteum degrades into a corpus albicanswithout embryo/fetus loss.

Structure

The corpus luteum is typically very large relative to the size of the ovary; in humans, the size of the structure ranges from under 2 cm to 6 cm in diameter. [1]Its cells develop from the follicular cells surrounding the ovarian follicle. The granulosa cells become the outer granulosa lutein layer and secrete progesterone. Theca interna cells become the inner theca lutein layer which secretes estrogen.

Reference

• Bagnell, C. 2005. "Animal Reproduction". Rutgers University Department of Animal Sciences.de:Gelbkörper

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It uses material from the http://en.wikipedia.org/wiki/Corpus+luteum Wikipedia article Corpus luteum.