Oogenesis

Question 1

Question 1: What is the definition of oogenesis?

Answer 1

It is the process of transformation of the oogonia into a mature ovum.

Question 2

Question 2: Where and when does oogenesis occur?

Answer 2

The steps of oogenesis occur in the cortex of the ovary.

They are accompanied by the development of ovarian follicles.

It starts as early as embryonic life.

Question 3

Question 3: What are the stages of oogenesis?

Answer 3

Prenatal maturation.

Postnatal maturation.

Question 4

Question 4: What is the source of embryonic germ cells during prenatal maturation?

Answer 4

They are derived from the endoderm of the wall of the yolk sac.

During their migration to the developing ovary (urogenital ridge), they differentiate into oogonia.

Question 5

Question 5: What happens in the ovary by the 3rd month of embryonic development?

Answer 5

The ovary contains nests of oogonia.

Oogonia proliferate by mitosis to produce primary oocytes.

About 1-2 million primary oocytes are present at birth.

No primary oocytes form after birth.

Question 6

Question 6: What is the structure of the primordial follicle?

Answer 6

Ovarian stromal cells surround the primary oocyte.

They form a single layer of flattened follicular cells.

The primary oocyte and its follicular cells constitute the primordial follicle.

Question 7

Question 7: What changes occur to the follicular cell layer at puberty?

Answer 7

The follicular cell layer becomes cuboidal.

A primary follicle (early) is formed as the primary oocyte enlarges.

A primary follicle with more than one layer of cuboidal cells is called a growing follicle.

Question 8

Question 8: When does the first meiotic division of primary oocytes begin and complete?

Answer 8

It begins before birth.

It is not completed until after puberty.

Question 9

Question 9: What happens to primordial follicles from birth to puberty?

Answer 9

Most primordial follicles degenerate.

By puberty, only about 30,000–40,000 primordial follicles remain.

Only 200–400 follicles reach full maturity and are expelled at ovulation.

The remaining follicles undergo atresia.

Question 10

Question 10: What happens to primary oocytes after birth?

Answer 10

They remain dormant in the ovaries until puberty.

Question 11

Question 11: What changes occur to the primary oocyte during follicular maturation?

Answer 11

The primary oocyte increases in size.

A membrane called the zona pellucida forms around it.

Question 12

Question 12: What happens during the first meiotic division of the primary oocyte?

Answer 12

It is completed just before or at the time of ovulation.

It gives rise to two daughter cells:

A secondary oocyte.

A first polar body.

Each cell contains 23 chromosomes (haploid number).

Question 13

Question 13: What happens to the secondary oocyte during ovulation?

Answer 13

Its nucleus begins the second meiotic division but arrests at metaphase.

If fertilization occurs, the mature oocyte retains most of the cytoplasm.

The second polar body degenerates.

Each cell contains 23 chromosomes.

Question 14

Question 14: What surrounds the secondary oocyte at ovulation?

Answer 14

zona pellucida and a layer of follicular cells called the corona radiata.

It is a large cell.

Question 15

Question 15: What is fertilization and its outcome?

Answer 15

Fertilization is the fusion of one sperm with one secondary oocyte.

It restores the diploid number of chromosomes (46).

Question 16

Question 16: What happens if fertilization does not occur?

Answer 16

The ovum undergoes autolysis without completing the second meiotic division.

Question 17

Question 17: What is the ovarian cycle?

Answer 17

A 28-day cycle of changes in the ovary of a fertile female every month.

Influenced by pituitary hormones (FSH and LH).

Question 18

Question 18: What are the phases of the ovarian cycle?

Answer 18

Follicular phase.

Ovulation.

Luteal phase.

Question 19

Question 20: What happens during the stage of primordial follicles?

Answer 19

15-20 primordial follicles grow under FSH effect.

Primary oocyte covered by a single layer of flattened cells.

Question 20

Question 22: What characterizes the mature primary (preantral) follicle?

Answer 20

Granulosa cells form a stratified layer around the oocyte.

Well-defined zona pellucida.

Question 21

Question 23: What happens during the stage of growing follicles?

Answer 21

The follicular cells become cuboidal in shape.

Granulosa cells form around the oocyte.

The zona pellucida forms between the oocyte and the surrounding granulosa cells.

A capsule-like layer called “theca” forms around the follicle.

Fluid-filled spaces appear between granulosa cells.

These spaces form the follicular cavity (antrum), and the follicle becomes a secondary follicle.

Question 22

Question 24: What happens during the vesicular (antral) stage of the follicle?

Answer 22

The oocyte is off-center and surrounded by the zona pellucida.

The antrum forms as fluid accumulates between cells.

Theca interna and externa cells surround the follicle.

Question 23

Question 25: What happens during the mature vesicular (Graafian) follicle stage?

Answer 23

The antrum enlarges and fills with follicular fluid.

The antrum is surrounded by granulosa cells.

The oocyte is surrounded by the cumulus oophorus.

Question 24

Question 1: What happens during the stage of the mature Graafian follicle?

Answer 24

The antrum enlarges, pushing the oocyte to one side.

Granulosa cells form the cumulus oophorus around the oocyte.

Granulosa cells around the zona pellucida become columnar, forming the corona radiata.

Granulosa cells around the cavity are called membrane granulosa.

The mature follicle is about 25 mm in diameter.

It is surrounded by theca interna and theca externa.

Granulosa and theca interna cells produce estrogen under FSH control.