Histology 2 Oogenesis

Front 1

What follicles are found in the cortex of the ovary?

Back 1

Primordial follicle, primary follicle, secondary (antral) follicle, mature (Graffian) follcile, corpus luteum, corpus albicans, and atretic follicles.

Front 2

Primordial follicles.

When are they made?
Effects of hormonal stimulation.
What type of oocyte is found in this follicle?
What stage of meiosis is the oocyte?

What surrounds the oocyte?

Back 2

Appear in the third month of fetal development.

Growth is independednt of hormonal stimulation.

Contain primary oocyte arrested in meiosis I.

Oocyte is surrounded by follicular cells, which is surrounded by basal lamina, which is surrounded by CT.

Front 3

Primary follicles.

Effects of hormonal stimulation.
What type of oocyte, and what stage is it in meiosis?
What is it surrounded by?
What happens to the CT surrounding the follicle?

Back 3

Primary follicles develop under the influence of follicle stimulating hormone (FSH), produced by basophils of anterior pituitary which binds to receptors on follicular cells.

Has primary oocyte still arrested in meiosis I.

The squamous follicular cells become cuboidal granulosa cells. Starts as unilaminar primary follicle, then proceeds to multilaminar. Primary oocytes secrete a new layer between it and granulosa cells called zona pellucida (composed of glycoproteins ZP1-4). Zona pellucida has receptor for sperm. Furthermore, cortical granules can be seen deep to the zona pellucida.

The CT surrounding the basal lamina specializes into theca interna and externa.

Front 4

Theca interna of CT surrounding primary follicle.

Function. What receptors do they have?

Back 4

Has endocrine characteristics and is well vascularized.

Theca interna have receptors for luteinizing hormone (LH), which is secreted by basophils in pars distalis of anterior pituitary.

In response to LH, theca interna secretes androgens and some progesterone.

Front 5

Theca externa of CT surrounding primary follicle.

Back 5

Less well vascularized than theca interna, and is simply a connectie tissue.

Front 6

Secondary (antral) follcle.

Defining characteristics.
Describe oocyte.
Effects of hormonal stimulation.

Back 6

Defining characteristic: appearance of fluid-filled space called antrum among granulosa cells.

Oocyte is still primary (arrested in meisosis I). Becomes eccentrically located with a mass of granulosa cells called cumulus oophorus. Granulosa cells which surround the oocyte is called corona radiata.

Hormonal stimulation is needed for continues growth: hormones include FSH, estrogen, and growth factors (from oocyte and theca), and calcium.

Front 7

In the secondary (antral) follicle, what is the antrum filled with?

Back 7

The antrum is filled with a fluid rich in hyaluronic acid. It also contains hormones and growth factors.

Front 8

What do granulosa cells do under the influence of FSH?

Back 8

Under the influence of FSH (secreted by anterior pituitary), granulosa cells convert androgens (secreted by theca interna) into estradiol (main form of estrogen). Estrogen stimulates granulosa cell proliferation.

Thus, LH (also secreted by anterioir pituitary) is important so that theca interna can produce androgens. Granulosa cells gradually begin to aquire LH receptors in addition to their FSH receptors.

Front 9

Graafian (mature) follicle.

Distinguishing characteristics. Describe the oocyte.

Back 9

Distinguishing characteristics: large antrum, detachment of oocyte and corona radiate from the cumulus oorphus. MOST IMPORTANTLY, the completion of meiosis I several hours before ovulation in response to an LH SURGE by anterior pituitary.

The oocyte then become a secondary oocyte and first polar body is formed. Then ovulation takes place.

Front 10

Describe ovulation.

What type of cells are released? What phase is the cell found in?

Back 10

During ovulation, a secondary oocyte is released, plus corona radiata cells, and cells of cumulus oophorus. Everything else remains in the mature follicle.

Front 11

Define luteinization

Back 11

Under the influence of the LH surge by ant. pituitary, the ramainder of the theca interna and granulosa cells of the mature follicle become filled with lipids. Their new function now is to produce progesterone.

Front 12

When does the secondary oocyte complete meiosis II?

Back 12

Only after fertilization when the membranes of the sperm and oocyte fuse. This results in the formation of an ovum and second polar body.

Front 13

Corpus luteum

How is it formed? Function. Hormonal influence.

Back 13

The remainder of the granulosa cells and theca interna cells now are luteinized and the mature follicle becomes a corpus luteum.

Function: produces progesterone, which maintains the endometrium (i.e. prevents menses)

Corpus luteum produces progesterone and some estrogen under the influence of human chorionic gonadotropin (hCG) from the placenta. This means if fertilization does not occur, the corpus luteum regresses to the corpus albicans (has a glassy, highly folded look).

Front 14

Atritic follicle.

How is it formed? Contrast to corpus albicans.

Back 14

Follicles that did not develop. Any follicle which shows signs of cell death.

Contrast to corpus albicans: smaller, and has a folded zona pellucida!