The Female Reproductive System

Question 1

How are primordial follicles formed in the first stage of folliculogenesis and what are they responsible for?

Answer 1

Primordial germ cells from primordial pool migrate to developing ovary around 5-6 into pregnancy and differentiate into oogonia which then multiply by mitosis. Once numbers have increased by mitosis, Primordial follicles form and the oocytes enter meiosis I.

At 16-24 weeks meiosis I is paused in prophase I ( ooctyes arrested meaning no more DNA replication) . Primordial follicles only resume growth after puberty, from then on they enter the menstrual cycle each month-> responsible for a woman’s menstrual cycle

Question 2

When are the primordial follicles formed?

Answer 2

During three fatal stage. Their development is paused as oocytes are arrested at weeks 16-24.

Question 3

Describe the structure of primordial follicles

Answer 3

A primordial follicle is a round structure that contains an immature egg cell/oocyte, surrounded by a single layer of flattened cells called granulosa cells (differentiated oocytes). These secrete an acellular basal lamina

Question 4

What happens after the primordial follicle has been formed?

Answer 4

The primary follicle is formed :

The oocyte enlarges. The surrounding Granulosa cells multiply by mitosis and the oocyte secretes zona pellucida ( glycoprotein layer). A second layer of theca cells differentiates around the basal lamina to form a primary follicle.

Question 5

What marks the transition from the primary follicle to the secondary follicle?

Answer 5

.The formation of multiple granulosa layers
and the beginning of small antrum (small fluid-filled spaces)

.Theca externa and interna surround the granulosa layers

Question 6

What is the role of theca interna and theca externa

Answer 6

Theca interna and theca externa surround the granulosa cells and are involved in hormone production

Question 7

What happens in the secondary follicle (Antral) stage ?

Answer 7

Granulosa cells further divide by mitosis, follicle becomes larger and antrum become larger. Cumulus cells are now present and surround the oocyte cells.

Question 8

What triggers the development of a dominant follicle?

Answer 8

Selections occurs in response to FSH and LH around 14 days into the menstrual cycle.
Therefore development of the secondary follicle is known as the FSH/LH dependant phase.

Question 9

What part of folliculogenesis is the FSH-independent stage and how long is it ?

Answer 9

The formation of the primary follicle from the primordial follicle is known as the FSH independent phase. This is approximately 65 days.

Question 10

The Menstrual cycle: ovaries

What is the follicular phase and when does it occur during the menstrual cycle?

Answer 10

Follicular phase: growth of follicles up to ovulation stimulated by FSH from pituitary; dominated by oestrogen produced by growing follicles

This happens in the first 14 days of the menstrual cycle

Question 11

Menstrual cycle: ovaries

What is the luteal phase and when does it occur

Answer 11

Luteal phase: formation of corpus luteum from the empty follicle; dominated by progesterone production from corpus luteum (temporary ovary after release of egg from ovary). This happens after ovulation and lasts for approximately 14 days- when corpus luteum is not fertilised, progesterone levels drop causing uterus lining to shed. (May lead to PM symptoms)

Prepares the uterus for pregnancy by thickening the uterus lining

Question 12

Menstrual cycle: uterus

1. What happens in the proliferative phase?

Answer 12

Proliferative phase:

Growth of endometrium under the influence of oestrogen. This happens in the first 14 days of the menstrual cycle.

Question 13

Menstrual cycle: uterus

What happens in the secretory phase ?

Answer 13

Maturation of endometrium under the influence of progesterone

Empty follicle becomes corpus luteum and secretes mainly progesterone- causes cervical mucus to become more vicious and impenetrable and causes endometrium to grow thicker

Question 14

What is a low antral follicle count a sign of?

Answer 14

Menopause

Question 15

In the ovarian follicular phase, what is follicle recruitment?

Answer 15

At the small antral stage, a dozen or so follicles become responsive to FSH and are recruited into the current cycle.

Question 16

The ovarian follicular phase, what is dominant follicle selection?

Answer 16

From the group that are recruited only one will become the dominant follicle and be selected for ovulation.

Question 17

What effect does increasing oestrogen have on FSH in the first 14 days of the menstrual cycle?

Answer 17

Causes FSH levels to decrease meaning that all follicles die (via apoptosis) apart from the selected dominant follicle, which also produces oestrogen to kill other follicles

Question 18

What happens to the endometrium in the proliferative phase?

Answer 18

Endometrium lining regrows and thickens.

Cervical mucus becomes increasingly watery under the influence of rising oestrogen levels throughout the proliferative phase

Question 19

What effect does oestrogen have on LH

Answer 19

Increased oestrogen = increased LH

Question 20

What effect does increased progesterone levels have on GnRH (FSH and LH )

Answer 20

As progesterone increases FSH and LH decreases

Question 21

How long is the corpus luteum lifespan and what happens after is regresses ?

Answer 21

14 days and will regress if pregnancy does not occur- causes fall in progesterone levels which in turn causes the endometrium to be lost.