Origins of Gametes - Female Gamete

Question 1

What part of the gonad do germ cells colonise?

And what do they become?

Answer 1

The gonadal cortex

They become oogonia

Question 2

Once the germ cells have colonised the gonads and produced oogonia, what do they do?

Answer 2

They proliferate rapidly by mitosis

Question 3

When do oogonia reach max number?

Answer 3

Mid gestation (7 million)

Question 4

What happens to most oogonia during gestation?

And what happens to the rest before birth?

Answer 4

Most die, normally about 2 million remain

The remaining 2 million all enter meiosis before birth

Question 5

Describe what initially happens to the oogonia which have started meiosis?

Answer 5

Meiosis stops at an early stage
These are now primary oocytes
They are surrounded by a singular layer of granulosa cells
forming primordial follicles

Question 6

What happens at puberty to the female gametes?

Answer 6

The follicles start to develop further

Only a small proportion develop at a time

Question 7

What happens to most developing gametes in a woman’s reproductive life?

Answer 7

Most die

Only about 400 or so survive and are released in a woman’s life out of 2 million

Question 8

What is the term for release of an ovum?

Answer 8

Ovulation

Question 9

How long is the period of fertility in a woman?

Answer 9

About 36 hours after the release of an ovum

Question 10

What is the human female reproductive cycle known as?

Answer 10

The menstrual cycle

Question 11

How long is the menstrual cycle?

Answer 11

Around 28 days

Question 12

What are the three main parts of the menstrual cycle?

And give a time period for each

Answer 12

Preparatory phase - days 0-12
Ovulation - around days 12-14
Waiting phase - days 14-28

Question 13

What is the preparatory phase known as in regards to the ovaries and uterus?

Answer 13

Ovaries - Follicular phase

Uterus - Proliferative phase

Question 14

What is the waiting phase known as in regards to the ovaries and uterus?

Answer 14

Ovaries - Luteal phase

Uterus - Secretory phase

Question 15

What happens at the beginning of the menstrual cycle?

Answer 15

A small number of gametes that have already started development begin to develop further

Question 16

At the beginning of the menstrual cycle primordial follicles develop into what?

Answer 16

Pre-antral follicles
The granulosa cells proliferate
A layer called the zona pellucida forms around the oocyte
Then lots of granulosa cell layers
And a final covering called a theca
This all happens independent of hormones

Question 17

What turns a pre-antral follicle into an antrum?

Answer 17

The formation of a small fluid filled cavity in the follicle.

Question 18

After an antrum forms what happens to the follicles?

Answer 18

Under the influence of FSH and LH one or two follicles grow to 20mm
Then the theca secretes oestrogen
This is a pre-ovulatory follicle

Question 19

After the mature follicle is formed, just before ovulation, what happens?

Answer 19

Meiosis restarts (continues)
This forms 2 daughter cells but only one is functional, it has all the cytoplasm, the other is just a packet of DNA that is discarded
This is the first division

Question 20

When does the second division of the oocyte occur?

Answer 20

After fertilisation

Question 21

What happens to the follicle after the oocyte has been released?

Answer 21

It forms a corpus luteum
Which grows under influence of LH
Secretes oestrogen and progesterone
And if it doesn’t receive a signal that the ovum has been fertilised, it kills itself.