Oogonia

Question 1

In the human, the process of oogenesis starts early in fetal development.
True or False

Answer 1

True

Question 2

The primordial germ cells proliferate and migrate from

Answer 2

the epithelium of the yolk sac => genital ridge via the embryonal endoderm reaching the gonadal ridges at about the 5th week of pregnancy.

Question 3

The primordial germ cells move from the gonadal ridges inwards to form the primitive medullary and sex cords. At this point they lose their motility and become _______________ which then _______________________.

Answer 3

A. Oogonia
B. Multiply by Mitosis

Question 4

Oogonia are _________ derived and intercellular cytoplasmic bridges between oogonia, a characteristic of nest formation by premeiotic gametes, have been observed in the human.

Answer 4

Clonally

Question 5

What are believed to arise from daughter cells derived from the same dividing oogonium and may help increase the store of materials and nutrients necessary for later development?

Answer 5

Oogonial nests

Question 6

Approximately ________ to _________ oogonia will arrive at the fetal ovary. They then increase dramatically in number through mitotic division to a maximum concentration of __________ oogonia by the _________________of gestation. At this point mitosis stops and no additional oogonia will develop.

Answer 6

A. 1000 to 2000
B. 6-7 million
C. 20th week (5th month)

Question 7

_____________ and _______________ have been demonstrated to be important for fetal ovary development, but information regarding their control and interactions is lacking.

Answer 7

Growth factors and neurotropins

Question 8

Experimental evidence indicates a possible role for many factors in oocyte development and survival including

Answer 8

A. Prostaglandins
B. Members of the transforming growth factor beta (TGFB) superfamily,
C. Bone morphogenetic proteins (BMPs)
D. Wingless-type mouse mammary tumor virus integration site (WNT) signaling molecules
E. Antimüllerian hormone (AMH)

Question 9

What are the general overall steps of oogenesis (including pre-birth steps)?

Answer 9

Pre-birth (fetal development)
1. Primordial Germ Cells: Primordial germ cells originate and migrate to the gonads (which become the ovaries) in the developing female fetus.
2. Oogonia Formation: Primordial germ cells undergo mitotic division, producing a large number of diploid oogonia.
3. Primary Oocyte Formation: The oogonia then enter meiosis I and differentiate into primary oocytes, which become arrested at prophase I.
4. Follicle Formation: Each primary oocyte is enclosed within a layer of follicular cells, forming primordial follicles.
5. Atresia: Many primary oocytes degenerate (atresia) throughout childhood, reducing the initial number significantly.
Post-birth (from puberty onwards)
6. Meiosis I Resumption: At puberty, hormones (like FSH) stimulate the development of follicles, leading to the resumption of meiosis I in some primary oocytes.
7. Secondary Oocyte & First Polar Body Formation: Meiosis I completes, producing two cells of unequal size: a secondary oocyte (which receives most of the cytoplasm) and a first polar body (a smaller cell). The first polar body usually degenerates.
8.0Meiosis II Arrest: The secondary oocyte begins meiosis II but arrests at metaphase II, awaiting fertilization.
9. Ovulation: During ovulation, the secondary oocyte is released from the follicle and moves into the fallopian tube, ready for potential fertilization.
10. Fertilization (optional): If fertilization occurs, the sperm penetrates the secondary oocyte, triggering the completion of meiosis II.
11. Ovum and Second Polar Body Formation: The completion of meiosis II results in the formation of a mature ovum (egg cell) and a second polar body, which also typically degenerates.
12. Zygote Formation: The nucleus of the ovum fuses with the sperm nucleus, forming a diploid zygote.

Question 10

What are the simple squamous epithelial cells which surround primary oocytes called?

Answer 10

granulosa cells

Question 11

What is the resting state of a follicle before it matures during the menstrual cycle after puberty has begun?

Answer 11

primordial follicle

Question 12

What is the acellular layer which directly surrounds the oocyte called and made of?

What produces it?

Answer 12

zona pellucida (ZP)

the oocyte and the follicle granulosa cells

Question 13

What are the cells surrounding the oocyte called once there is more than one layer?

Answer 13

Once there is more than one layer of cells surrounding the oocyte, these cells are broadly called granulosa cells. The innermost layer is the corona radiata, and the entire cluster is the cumulus oophorus.

Question 14

What is the fluid filled space within a follicle called?

What is it filled with?

When does it form?

Answer 14

The antrum

Follicular fluid

During the late stages of growth in the secondary follicle, a clear fluid begins to accumulate between some granulosa cells. When the follicle reaches approximately 400 μm in diameter, the fluid coalesces into a crescentic space called the antrum.

Question 15

What is the largest, most mature follicle stage?

How big is it?

Answer 15

Graafian follicle, also known as the preovulatory follicle

12–19 mm

Question 16

What are the innermost 1-3 cell layers around the oocyte called?

Answer 16

corona radiata

Question 17

What are the two outer cellular layers of the Graafian follicle called?

Their functions/structural characteristics?

Answer 17

Theca interna and externa

The theca interna is primarily responsible for producing androgens (like testosterone), which are then converted to estrogen by neighboring granulosa cells. The theca externa, on the other hand, provides structural support to the follicle and plays a role in ovulation.

Question 18

What does the Graafian follicle become after ovulation?

And what does it do?

Answer 18

corpus luteum

Produces E and P

Question 19

What marks the change to (or characterizes) a secondary follicle?

Answer 19

2 layer of GCs and appearance of theca cell