Ovarian follicles; Histology - March 2015

powerpoint presentation in Histology about "Ovarian follicles". It was made in March 2015.

1. Ovarian follicles

2. Prepared by: Kareem Fisal Alnakeeb Supervised by: Dr. Hanaa Khalaf

3. Ovarian follicles are the basic units of female reproductive biology Composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte (immature ovum). The primary role of the follicle is oocyte support The ova are developed only once every menstrual cycle A woman begins puberty with about 400,000 follicles Ovarian follicles

4. A- Primordial follicle B- Primary follicle C- Secondary follicle D- Graffian follicle * Corpus luteum Development of Ovarian follicles ( folliculogenesis )

5. D- Graffian follicles C- Secondary ( Growing ) follicles B- Primary follicles A- Primordial follicles Bulging on the surface of ovary Deep in the cortex under the Tunica albuginea under the Tunica albuginea Site 1/28 days Numerous & in groups Numerous & in groups Number The largest Double its size larger small Size 2 ry oocyte Follicular cells : 1. Cumulus oophorus 2. Granulosa Cells 3. Corona Radiata Zona pellucida Theca folliculi : 1. Interna 2. Externa 1 ry oocyte Follicular cells : 1. Cumulus oophorus 2. Granulosa Cells Zona pellucida Theca folliculi 1 ry oocyte Follicular cells : cubical Then columnar 1 ry oocyte Follicular cells : simple squamous Structure

6. 2 ry oocyte in Graffian follicles 1 ry oocyte of Growing follicles 1 ry oocyte of Primary follicles 1 ry oocyte of Primordial follicles 1 st Meiosis of 1 ry oocyte From Primordial germ cells of yolk sac These cells migrate to the ovaries Form the oogonia Which enlarge & Form 1 ry oocyte Origin 120 µ m 60 µ m larger 30 µ m Size 23 d-chromosomes 46 d-chromosomes Nucleus Full of yolk granules More yolk granules More yolk granules Few yolk granules Cytoplasm Microvilli into Zona pellucida Microvilli into Zona pellucida Usual cell organoids Usual cell organoids E/M

7. Number : 4 to 5 million Site : usually found close to the outer edge of the cortex i.e. under Tunica albuginea Size : small Structure : 1. 1 ry oocyte Nucleus : Large – vesicular – rounded – eccentric – 46-d chromosomes Cytoplasm : pale – acidophilic – few yolk granules 2. Follicular cells single layer of flat , squamous granulosa cells (the support cells) separated from the oocyte by the basal lamina . A- Primordial follicles

8. In primordial follicles, the oocyte is arrested in the last stage of prophase (known as dictyotene ).

9. The granulosa cells of primordial follicles change from a flat to a cuboidal structure Then columnar The oocyte genome is activated and genes become transcribed. The oocyte enlarges, and the follicular cells divide. Primary follicles develop FSH receptors , but they are gonadotropin- in dependent until the antral stage . B- Primary follicles

10. Also called Growing Follicles or antral follicle The secondary follicles look very similar to primary follicles, except that 1. they are larger 2. there are more follicular cells In Response to FSH 3. there are small accumulations of fluid in the intracellular spaces called  follicular fluid   (nutritive fluid for the oocyte – secreted by follicular cells In Response to LH ). These gradually coalesce to form an  antrum . C- Secondary Follicles

11. The antrum divides follicular cells into : 1) Cumulus oophrous : surround oocyte & connect it to one side of follicle 2) Granulosa Cells Line the cavity & secrete Estrogen Polygonal in shape Pale acidophilic cytoplasm Central Rounded Nuclei A thick glycoprotein layer develops between the oocyte and the zona granulosa , called the zona pellucida ** Stained with PAS the stroma around the follicle develops to form a capsule like 'theca ' . (Theca is greek for 'box ').

12. primordial follicles transitional follicle from the primordial to the primary stage primary follicle secondary follicle antral follicle atretic follicle

13. Also called Tertiary vesicular follicles or mature vesicular follicles The secondary follicle develops into a Graffian follicle. After the first meiotic division, most of the cytoplasm goes into one of the two daughter cells & becomes secondary oocyte & The other becomes the polar body D- Graffian follicles

14. The folicular fluid fills a single space, called the antrum The Antrum 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 . The follicular cells surrounding zona pellucida known as the corona radiata

15. basal lamina (follicular basement membrane) thin layer of extracellular matrix (fibro-vascular coat) that enclose granulosa cells i.e. between the granulosa cells and the theca interna . Theca folliculi The surrounding theca differentiates into two layers: 1.Theca interna ( Vasculosa ) rounded cells that secrete androgens and follicular fluid The androgens are converted into estrogen by the granulosa cells. 2. Theca externa ( Fibrosa ) more fibrous - spindle shaped cells - merges with the surrounding stroma .

16. oocyte cytoplasm * corona radiata Arrow antrum A follicular cells F theca layers T Mitochondria M vestibular bodies Vb zona pellucida Zp spaces H

17. The oocyte, zona pellucida and 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 fertilized . Fate of Graffian follicle

18. Formation : After ovulation, the ruptured follicle collapses and fills with a blood clot ( corpus haemorrhagicum ) which then forms the corpus luteum . Size : The corpus luteum takes up one third of the ovary. Function : The corpus luteum secretes estrogen (which inhibits FSH) and relaxin (which relaxed the fibrocartilage of the symphysis pubis) . Corpus luteum

19. Structure : The remaining part of Ovarian follicle after ovulation i.e granulosa cells - theca interna - theca externa The granulosa cells enlarge, and become vesicular & become folded and are now called the granulosa lutein cells . They secrete progesterone 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 . They secrete estrogen The remaining part of theca externa surrounding Corpus luteum is known as Fibrous capsule

20. About 20 primordial follicles start developing in each cycle, but only ONE makes it ! & becomes mature The remaining follicles degenerate & replaced by fibrous C.T called Atretic follicle or corpus atreticum Some cells of theca interna will form Interstitial glands of ovary