Histology and Functions

Histology and FunctionsOf the OVARYWhat does Histology mean? Histology is the study of the microscopic structure of tissues.

What are Ovaries? Are reproductive organs that produces ova and, in vertebrates, estrogen and progesterone.This shot shows some of the different areas of the ovary that are being studied.

Structure of an Ovary

Primordial Follicle A primordial follicle is a primary oocyte in the outer region of the cortex. It is arrested in the first meiotic prophase. It is surrounded by flattened follicular epithelial cells.Primary FollicleThe primary follicle is marked by the surrounding of flattened (squamous) follicular cells becoming cuboidal and the oocyte becomes bigger. Secondary Follicle The presence of the antrum is a characteristic of a secondary follicle. A follicle at this stage is also called an "antral follicle".Graffian FollicleThe mature follicle is also called the Graffian follicle. The follicle which is ovulated is the Graffian follicle. The connective tissue layer around the primary follicle is the theca folliculi. The follicular cells are granulosa cells. The acidophilic glycoprotein coat surrounding the oocyte is the zona pellucida. A cavity within the follicle is the antrum.Corpus Luteum"Yellow body". The corpus luteum forms from a Graaffian follicle after the release of the oocyte.Corpus Albicans"White body". Remnant from corpus luteum.

4Ovaries also have an endocrine function - they release oestrogen and progesterone. The ovaries are small almond shaped structures, covered by a thick connective tissue capsule - the tunica albuginea. This is covered by a simple squamous mesothelium called the germinal epithelium. The ovary has a cortex, which is where the ovarian follicles can be found, and a highly vascular medulla, with coiled arteries called helicrine arteries.The oocytes are surrounded by epithelial cells and form follicles. The ovary contains many primordial follicles, which are mostly found around the edges of the cortex. There are fewer follicles in different stages of development.

The Ovary

Ovarian Follicles Primary Follicle

Secondary Follicle

Primary follicleWhen the primordial follicle is stimulated, it becomes a primary follicle. The oocyte enlarges, and the follicular cells divide. A follicle that has two layers of follicular cells is called a primary follicle. These cells continue to hypertrophy and proliferate to form many layers surrounding the oocyte. Eventually these cells become known as 'granulosa' cells. The granulosa cells will secrete progesterone after ovulation.A thick glycoprotein layer develops between the oocyte and the zona granulosa, called the zona pellucida.Finally, the stroma around the follicle develops to form a capsule like 'theca'. (Theca is greek for 'box'). Only one of the maturing follicles completes the maturation process each month. The rest degenerate into atretic follicles. Follicular maturation takes about 3 months.

Secondary FollicleThe primary follicle develops into a secondary follicle.The secondary follicles look very similar to primary follicles, except that they are larger, there are more follicular cells, and there are small accumulations of fluid in the intracellular spaces called follicular fluid (nutritive fluid for the oocyte). These gradually coalesce to form an antrum. The surrounding granulosa cells is called the cumulus oophorus (greek for 'egg bearing heap').The surrounding theca differentiates into two layers: the Theca interna (rounded cells that secrete androgens and follicular fluid) and a more fibrous Theca externa - spindle shaped cells. The androgens are converted into oestrogen by the granulosa cells

6Ovarian Follicles continued..Graffian follicle

Corpus Luteum

Graffian follicle.The secondary follicle develops into a Graffian follicle.The first meiotic division is now completed, and the oocyte is now a secondary oocyte, and starts its second meiotic division. After the first meiotic division, most of the cytoplasm goes into one of the two daughter cells. The other becomes the polar body (hard to see). The folicular fluid fills a single space, called the antrum, which is surrounded by the follicular cells - called the membrana granulosa. The granulosa cells that surround the oocyte, and project into the antrum are called as the cumulus oophorus. There is a basement membrane between the granulosa cells and the theca interna. The fibrous theca externa merges with the surrounding stroma.The oocyte, zona pellucida and the follicular cells surrounding the ooctye (known as the corona radiata) are all expelled at ovulation, and enter the fallopian tube.Once released, the oocyte begins its second meiotic division, as far as metaphase II. Division only carries on if the ovum is fertilised.

Corpus LuteumAfter ovulation, the ruptured follicle collapses and fills with a blood clot (corpus haemorrhagicum) which then forms the corpus luteum. The granulosa cells enlarge, and become vesicular, and are now called the granulosa lutein cells. these become folded, as you can see here. The spaces between the folds are filled with theca interna cells, which also enlarge and become glandular, and are now known as the theca lutein cells. The zona granulosa cells begin to secrete progesterone (granulosa lutein cells). The corpus luteum also secretes oestrogen (which inhibits FSH) and relaxin (which relaxed the fibrocartilage of the pubic symphysis). If pregnancy does not occur, then the corpus luteum degenerates into the corpus albicans, and levels of oestrogen and progesterone fall, allowing release of FSH and LH.If pregnancy does occur, then the syncytiotrophoblasts of the placenta release human chorionic gonadotrophin, and the corpus luteum persists.About 20 primordial follicles start developing in each cycle, but only ONE makes it!This image shows a corpus luteum in a human ovary. (from anatomy.iupui.edu) It takes up one third of the ovary.

7Corpus albicans

Corpus albicansThis image shows an atretic corpus luteum or corpus albicans. The cellular elements have degenerated, and macrophages phagocytose the dead cells. Fibrous tissue is left behind. The corpus albicans looks pale. It will continue to shrink, eventually forming a small scar on the side of the ovary.

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^ primordial follicle < 1st primary follicle < 2nd primary follicle

The primordial follicle makes about 20 eggs a month. These cells are resting in prophase these oocyte are typically surrounded by a single layer of follicular cells. In the 1st primary follicle the follicular cells enlarge and become cuboidal they later from the corona radiata and the oocyte itself becomes larger. In 2nd follicle the Zona pellucida is made up of carbs, the follicular epith becomes stratified which becomes known as stroma granulosum. After this process the Theca cells from the surrounding CT begin to be seen. These cells are actually called stromal cells layering themselves into two layers.

9There are 2 main functions of the ovaries :They produce gamete (oocytes) as well as the production of the hormones progesterone and estrogen. The ovaries are made of Tubular poles which are connected to the suspensory ligament and a uterine pole which connects to the uterus via the proper ligament of the ovary. An external cortex and internal medulla which is rich in CT, lymph, a/v also can be found here. Both hormones (progesterone, estrogen) play key roles in the menstrual cycle. Stages of Follicle Maturation

The function of the ovaries or female gonads are: An endocrine gland, producing ova An endocrine gland, secretinga. the female hormones estrogen and progesteroneb. androgens, typically considered male hormones. One site that has some great pictures of the different areas of cell for an ovary is:

http://anatomytopics.wordpress.com/2009/01/01/31-the-anatomy-histology-and-development-of-the-ovary/11References

http://www.histology-world.com/factsheets/ovary1.htm (slide 4)http://www.histology.leeds.ac.uk/female/FRS_ovarian_fol.php (slide 5,6,7,8)http://anatomytopics.wordpress.com/2009/01/01/31-the-anatomy-histology-and-development-of-the-ovary/ (slide 9)