Early Embryology

Question 1

What are oogoniums?

Answer 1

Diploid (2n) stem cells.

Question 2

What happens to oogoniums during pre-puberty?

Answer 2

They are converted into primordial follicles (which are arrested in prophase I)

Question 3

What stimulates primordial follicles to develop into primary follicles?

Answer 3

Localized androgens at puberty

Question 4

Describe a primary follicle.

Answer 4

Contains a primary oocyte, frozen in prophase I, surrounded by a single layer of granulosa cells.

Question 5

What hormone stimulates the conversion of a primary follicle to an early secondary follicle?

Answer 5

Follicle-stimulating hormone (FSH).

Question 6

What does FSH stimulate in the primary follicle?

Answer 6

Proliferation of granulosa cells and formation of the zona pellucida around the oocyte.

Question 7

How is oestrogen produced by LH and FSH?

Answer 7

LH stimulates theca cells to convert cholesterol into androgens, which are converted into oestrogen in granulosa cells by FSH stimulation.

Question 8

Describe an early secondary follicle.

Answer 8

Contains a primary oocyte with a zona pellucida, arrested in prophase I, surrounded by multiple layers of granulosa cells.

Question 9

What additional development occurs in the late secondary follicle?

Answer 9

Formation of pockets of follicular fluid containing hyaluronic acid.

Question 10

Describe the transformation from the late secondary follicle to the Graafian follicle.

Answer 10

FSH stimulates granulosa cells to produce more follicular fluid, merging pockets into a single cavity called the antrum.

Question 11

Describe a Graafian follicle.

Answer 11

Contains a secondary oocyte arrested in metaphase II, with an antrum filled with follicular fluid and surrounded by the corona radiata.

Question 12

What is the corona radiata?

Answer 12

Cells directly wrapping around the secondary oocyte

Question 13

What are the overall products of the follicular phase (days 1-14)?

Answer 13

1. Mitosis of granulosa cells
2. oestrogen production
3. follicular fluid
4. transformation of the primary oocyte into a secondary oocyte.

Question 14

What happens during the early follicular phase regarding hormone regulation?

Answer 14

Oestrogen provides negative feedback, inhibiting GnRH, FSH, and LH release, leading to a drop in oestrogen.

Question 15

What is the LH surge and when does it occur?

Answer 15

A surge in LH levels around days 13-14, triggered by rising oestrogen, leading to increased GnRH and LH release.

Question 16

What is the result of the LH surge on the Graafian follicle?

Answer 16

Increases follicular fluid production and activates proteases, leading to ovulation and release of the secondary oocyte.

Question 17

What does the secondary oocyte retain after ovulation?

Answer 17

Zona pellucida and corona radiata.

Question 18

What is the corpus hemorrhagicum?

Answer 18

The structure formed from the Graafian follicle filled with blood post-ovulation.

Question 19

What does the corpus luteum do?

Answer 19

Releases progesterone and inhibits further FSH release, supported by LH.

Question 20

What occurs during the luteal phase (days 15-28)?

Answer 20

The corpus luteum is formed, primarily involving LH, and progesterone is released to maintain the uterine lining.