3. Oogenesis and Follicular Development

Question 1

What makes up the fundamental female reproductive unit?

Answer 1

Single ovarian follicle, composed of one germ cell (oocyte), surrounded by endocrine cells

Question 2

What is menarche?

Answer 2

Beginning of menstrual cycles avg 11-13yrs

Question 3

What determines age at puberty?

Answer 3

–  genetics
–  nutrition
– geographic loca:on
– exposure to light
– body composi:on, fat deposition 
–  exercise

Question 4

What controls the menstrual cycle?

Answer 4

Gonadotropins and gonadal hormones

Question 5

What are the 3 phases of the ovarian cycle?

Answer 5

1. Follicular phase av 15days (ranges from 9-23 days)
2. Ovulatory phase: 1-3 days (and culminates with ovulation)
3. Luteal phase: 13 days (is less variable than follicular)

Question 6

What are the three phases of the endometrial cycle?

Answer 6

Menstruation
Proliferative
Secretory

Question 7

What are 4 function of the ovaries?

Answer 7

1. OOGENESIS ie production of gametes during the foetal period
2. MATURATION of oocyte
3. EXPULSION of the mature oocyte (ovulation)
4. SECRETION of female sex steroid HORMONES (oestrogen & progesterone) and peptide hormone inhibin.

Question 8

What is oogenesis?

Answer 8

The process when a developing egg (oocyte) differentiates into a mature egg (ovum)
Involves completion of meiosis which occurs at the time of fertilisation

Question 9

Progression from oogonia to primordial follicle?

Answer 9

Oogonia produced by mitotic division (max # about 7m)
At 8-10wks of gestation, prophase of 1st meiosis starts. Oogonia becomes primary oocyte.
Primary oocyte is surrounded by pre-granulose cells. Called primordial follicle

Question 10

What is mitosis?

Answer 10

Process of cell division that results in two genetically identical daughter cells developing from a single parent cell

Question 11

What is meiosis?

Answer 11

Division of a germ cell involving two fissions of the nucleus and giving rise to four gametes. Each possessing half the number of chromosomes of the original cell

Question 12

Describe the first phase of oogenesis that occurs during foetal life?

Answer 12

1. Oogonia develops in the embryonic yolk sac 3 weeks post conception.
2. Migrates to ovary
3. Colonise the cortex
4. Undergo mitosis
5. At 8-10 weeks meiosis begins
6. 1-2 million oocytes around the time of birth (reduces to 400,000 around puberty)
7. Remaining oocytes are arrested in meiotic prophase until last oocytes are ovulated

Question 13

Most common cytogenetic abnormalities associated with age…

Answer 13

Aneuploidy

Down syndrome

Question 14

Describe the 2nd phase of oogenesis at ovulation?

Answer 14

Meiosis resumes (stimulated by LH)

• The first division of meiosis is completed and the haploid nuclei now separates to form 2 cells
• The cytoplasm is unequally shared forming a large secondary oocyte and a polar body (with no further role)
• Meiosis arrests again at metaphase II and the secondary oocyte is ovulated
• 2nd divison of meiosis is only completed in those oocytes that are fertilised

Question 15

Spermatgenesis vs oogenesis

Answer 15

1. In females, mitotic proliferation of oogonia occurs prior to birth.
2. In males, spermatogonia proliferate only ader puberty.
3. In females, meiotic divisions of oocyte produces only one mature ovum.
4. In males, meiotic divisions of primary spermatocyte produces 4 mature spermatozoa.
5. In females, second meiotic division is completed only upon fertilisation.
6. In males, the products of meiosis (spermatids) undergo substantial differentiation in the maturing process.

Question 16

Oogenesis:
Continuous?
Temp?
Begins?
Stem cells?
Mobile gametes?

Answer 16

Discontinuous
Normal body temp
Meiosis begins before birth (initial stimulus is not steroidal)
Results in production of finite numbers of oocytes (ovary has no stem cells)
Results in production of immobile gametes

Question 17

Spermatogenesis:
Continuous?
Temp?
Begins?
Stem cells?
Mobile gametes?

Answer 17

Continuous
Lower than body temp
Meiosis begins at puberty (Indirectly dependent on progesterone)
Results in production of infinite numbers of sperm (testis has a stem cell population)
Results in production of motile gametes

Question 18

Eggs exist in ovaries in structures known as….

Answer 18

follicles

Question 19

Follicle development

Answer 19

1. Primordial follicle = single layer of granulosa cells around oocyte.
2. Oocyte size increases, multiple layers of granulosa cells + separation of oocyte from granulosa cells by zona pellucida.
3. BUT cytoplamic processes cross the zona pelucida and form gap junctions with oocyte and nutrients and chemical messengers are passed to oocyte.
4. Follicle grows by mitosis of granulosa cells and some differentiate to become theca
5. Antrum begins to form from amongst granulosa cells from fluid they secrete

Question 20

Features of small follicles (primordial)

Answer 20

Most numerous
Non-growing (stock pile)
Oocyte nucleus is in meiotic prophase
Single layer of follicular cells (granulosa cells)

Question 21

What hormone is secreted by primordial follicles?

Use?

Answer 21

Secrete anti-Mullerian hormone (AMH).

Level reflects the ovarian follicular reserve and therefore can be measured to assess ovarian ageing

Question 22

At puberty she has ≈ _____ oocytes
• she may experience ___ cycles
• she loses approx. ___ per cycle

Answer 22

At puberty she has ≈ 300,000 oocytes
She may experience 450 cycles
She loses approx. 650 per cycle

Question 23

What are the stages of medium follicle development?

Answer 23

Throughout life, cohorts of small follicles recruited to begin a period of slow growth
Follicular cells divide, forming 3 layers around the oocyte
Growth in independent of hormones
Takes 85 days (3 cycles) to reach three layers of follicular cells

Question 24

Other names for large follicles?

Answer 24

Secondary
Antral
Graafian
Preovulatory

Question 25

Stages of development of large follicles?

Answer 25

FSH stimulates rapid development of medium follicles over 14 days, leads either to ovulation or to atresia.

1. Zona pellucida develops and encloses the oocyte, masking its antigens
2. Rapid mitotic division in follicular cells forms many layers
3. Antrum develops and fills with fluid

LH activates the theca interna to synthesise androstenedione (the precursor for estadriol 17-beta synthesis by granulosa cells.)

Question 26

Initial growth is _________ of hormones and takes ___ days

Final growth is _________ on FSH and takes ______ days

Answer 26

Initial growth is independent of hormones and takes 85 days

Final growth is dependent on FSH and takes 10 – 14 days

Question 27

What are the chemical components of ovulation?

Answer 27

LH surge
FSH (some LH)
Prostaglandins E and F
"Stigma"
Process facilitation by intrafollicular pressure and contraction of smooth muscle in theca

Question 28

Influence of LH surge on ovulation

Answer 28

Induces prostaglandin endoperoxide synthase in granulosa cells (sets up
pseudoinflammatory response)

Question 29

Influence of FSH (and some LH) on ovulation?

Answer 29

Stimulates release of plasminogen activator from granulosa cells (converts
plasminogen to plasmin)

Question 30

Influence of prostaglandins E and F on ovulation?

Answer 30

Release lysosomal enzymes that digest follicular wall – not completely
understood

Question 31

Influence of “stigma” on ovulation?

Answer 31

Forms on surface of follicle, balloons out, forms vesicle and ruptures.
Oocyte is expelled

Question 32

Process of corpus lute formation?

Answer 32

• Mature follicle discharges its antral fluid and egg.
-Collapses around antrum and undergoes rapid
transformation.

• Granulosa cells enlarge, and form gland-like structure ie CORPUS LUTEUM

• Corpus luteum secretes:
-Oestrogen, progesterone, inhibin

• If no egg fertilisation, CL developments reaches maximum within approx 10 days
-Rapidly degenerates by apoptosis