Lecture 4 - Ovarian Function

Question 1

At what stage of development do the primordial germ cells migrate and where do they migrate to?

Answer 1

They migrate in weeks 3-7 and they migrate to the genital ridges. This is by chemotaxis

Question 2

What must be absent for the female gonads to form?

Answer 2

SRY gene

Question 3

How do the primordial follicles form? what cells do they contain?

Answer 3

The sex cord cells cluster around the primordial germ cells but do not penetrate deeply. This forms the primordial follicles that contain the granulosa cells.

Question 4

Why does normal oocyte development not occur in turners syndrome?

Answer 4

Both X chromosomes must be present for normal oocyte development. Normal overy development also requires normal germ cells.

Question 5

What are the 5 stages of development of the oocyte?

Answer 5

Primordial germ cells
Oogonium
Primary oocyte
Secondary oocyte
Mature oocyte

Question 6

Which stages of oocyte development do meiosis occur?

Answer 6

Primary oocyte undergoes meiosis to secondary oocyte

Secondary oocyte undergoes meiosis to form mature oocyte.

Question 7

When do the two steps of meiosis occur in females and what is this controlled by?

Answer 7

Meiosis one occurs when the female is in utero which means she is born without any primordial germ cells.
Meiosis two occurs at fertilisation so there can be a very long period between meiosis 1 and 2.

Question 8

In males the first and second meiosis give rise to 4 sperm cells, what happens for females?

Answer 8

The two meiosis divisions result in only one oocyte being produced and two polar bodies.

Question 9

How can polar bodies help determine if fertilisation has occured?

Answer 9

There will be a polar body present from the second meiotic division if fertilisation has occured.

Question 10

What are the equivalent of sertoli and leydig cells for females?

Answer 10

Sertoli cells are granulosa cells

Leydig cells are theca cells

Question 11

How long does it take from the inital development of a primordial follicle to ovulation?

Answer 11

375 days approx.

Question 12

What is the structure of the primordial follicle and what occurs in this stage?

Answer 12

It is the oocyte surrounded by a single layer of flattened granulosa cells.
Oocyte begins to grow

Question 13

How often do primordial follicles form?

Answer 13

They form every few days after puberty and are independent of the menstrual cycle.

Question 14

What is the structure of the primary follicle?

Answer 14

Granulosa cells become more cuboidal and theca cells and zona pellucida bein to become visible.

Question 15

What is the structure of the secondary follicle?

Answer 15

Granulosa proliferate, theca cells divide into two layers, interna and externa

Question 16

What is the structure of the mature follicle?

Answer 16

Granulosa cells secrete follicular fluid and the oocyte is surrounded by a corona radiata.

Question 17

How are follicles often divided into two catagories?

Answer 17

Pre-antral and post-antral

Question 18

What is the role of oestrogens?

Answer 18

They cause follicle maturation and prepare the endometrium for pregnancy.
Thin the cerical mucus
Help development of secondary sexual characteristics

Question 19

What is the role of progesterone?

Answer 19

It is produced by the corpus luteum post ovulation. It maintains the lining of the uterus thoughout pregnancy.

Question 20

What is the two cell hypothesis for the production of oestrogen?

Answer 20

That testosterone is produced by the theca cells which moves to the granulosa cells where it is converted to oestrogen by aromatase.

Question 21

What effects do FSH and LH have on the theca and granulosa cells?

Answer 21

FSH causes increased aromatase activity in granulosa cells

LH causes increased cholestrol uptake by theca cells

Question 22

What are the three phases of the medstrual cycle?

Answer 22

Follicular phase
Ovulation
Luteal phase

Question 23

What happens in the follicular phase?

Answer 23

GnRH cause secretion of FSH from the pituitary. This causes development of granulosa and theca cells into follicles. This causes production of oestrogen that causes an LH spike from the pituitary just before ovulation.

Question 24

What happens in the ovulation phase?

Answer 24

The oocyte enters meiosis 2 and arrests at the metaphase.

Ovulation

Question 25

What happens in the luteal phase?

Answer 25

Corpus luteum forms
Granulosa cells produce oestrogen and progesterone
Negative feedback from progesterone causes FSH and LH to fall.

Question 26

How does luteolysis occur?

Answer 26

after around 12 days if there is no hCG from an embryo then the corpus luteum begins to degrade.