Corpus luteum

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Corpus luteum
Image:Illu ovary 2.jpg
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Image:Gray1163.png
Section of the ovary. 1. Outer covering. 1’. Attached border. 2. Central stroma. 3. Peripheral stroma. 4. Bloodvessels. 5. Vesicular follicles in their earliest stage. 6, 7, 8. More advanced follicles. 9. An almost mature follicle. 9’. Follicle from which the ovum has escaped. 10. Corpus luteum.
Gray's	subject #266 1256
Dorlands/Elsevier	c_56/12260569

The corpus luteum (Latin for "yellow body") is a 1 mm, temporary endocrine structure in animals.

1 Development and structure
2 Function
- 2.1 When egg is not fertilized
- 2.2 When egg is fertilized
3 Additional images
4 External links
5 Reference

[edit] Development and structure

It develops from an ovarian follicle during the luteal phase of the estrous cycle, following the release of a mature egg from the follicle during ovulation. (Technically, the body formed immediately after ovulation is called the corpus hemorrhagicum, but this is a transitory stage, and is sometimes omitted from summaries.) While the egg traverses the Fallopian tube into the uterus, the corpus luteum remains in the ovary.

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. <ref>"Corpus Luteum Cyst of Pregnancy" at drspock.com</ref>

Its cells develop from the follicular cells surrounding the ovarian follicle:

Source	Becomes	Secretion
The granulosa cells	the outer granulosa lutein layer	progesterone
Theca interna cells	the inner theca lutein layer	estrogen

The granulosa cells which are stimulated by FSH mainly secrete estrogen, whereas Theca interna cells are stimulated by LH to produce androstenedione, which via a few steps, gives the granulosa the precursor for estrogen manufacturing. <ref>Boron & Boulpeap Medical Physiology updated edition 2005 p1153-1155</ref>

[edit] Function

It is essential for establishing and maintaining pregnancy in females.

In the ovary, the corpus luteum secretes estrogens and progesterone, which are steroid hormones responsible for the thickening of the endometrium and its development and maintenance, respectively.

[edit] When egg is not fertilized

If the egg is not fertilized, the corpus luteum stops secreting progesterone and decays (after approximately 14 days in humans). It then degenerates into a corpus albicans, which is a mass of fibrous scar tissue.

The uterine lining sloughs off without progesterone and is expelled through the vagina (in humans and some great apes). In an estrus cycle the lining degenerates back to normal size.

[edit] When egg is fertilized

If fertilized, however, the placenta 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 vessels in which the zygote(s) can develop. From this point on, the corpus luteum is called the corpus luteum graviditatis.

The introduction of the hormone prostaglandin at this point causes the degeneration of the corpus luteum and the abortion of the fetus. However, in placental animals such as humans the placenta eventually takes over progesterone production and the corpus luteum degrades into a corpus albicans without embryo/fetus loss.