Lecture 3: Female reproductive tract 1

Question 1

What is oogenesis?

Answer 1

• The process where an oogonia –> mature oocyte
• developed within a follicle

Question 2

Explain the embryonic development of oocytes

Answer 2

• Primordial germ cells in yolk sac migrate from yolk sac to the genital ridges (undifferentiated at this point)
• At genital ridges couple 100 oogonia –> 7 million oocytes at 6 months (mitosis) –> about 1 million at birth
• Meosis halts at prophase 1 until ovulation, cells at this point called primary oocytes

Question 3

Give an overveiw of the ovarian cycle?

Answer 3

• FSH and LH surges cause waves of about 30-50 follicles –> secondary follicles. Takes about 2-3 months
• 15 - 20 secondary follicles are stimulated to undergo rapid growth. Takes about 2 weeks. These are “follicular waves”. Some lost by atresia
• In humans 1-2 teriary follicles become dominant which are ovulated

Question 4

What are the Phases of the Ovarian Cycle?

Answer 4

Follicular Phase:development of the follicle in response to follicle stimulation hormone (FSH). As luteinizing hormone (LH) and FSH levels increase they stimulate ovulation, or the release of a mature oocyte into the fallopian tubes.

Luteal Phase: the corpus luteum forms on the ovary and secretes many hormones, most significantly progesterone, which makes the endometrium of the uterus ready for implantation of an embryo.

Question 5

How to identify primordial follicle?

Answer 5

• Flattened granulosa cells

Question 6

Main difference between primordial follicle and primary follicle?

Answer 6

• Cuboidal granulosa cells
• still contain primary oocyte
• formed post puberty

Question 7

Secondary Follicle

Answer 7

• Defined by an oocyte covered by multiple layers of cuboidal granulosa cells.
• These cells present FSH receptors, which causes proliferation and production of hormones.

These produce oestrogen (talk to pit. and hypo.), inhibin (talks to pituitary) and AMH (talks to a number of proceses)

• Theca Cells (like leydig cells): start to see a layer forming in the stroma, which have LH receptors to produce androgens

Question 8

What is oestrogen formed from?

Answer 8

Progesterones (from cholesterol) are the first step in the steroid hormone pathway.

Progesterone ⇒ androgen ⇒ oestogens

So oesstrogens (female hormone) comes after the male androgen hormone.

Question 9

Zona Pellucida

Answer 9

The thick transparent membrane surrounding a mammalian ovum before implantation.
Made up of 3 proteins (ZP-1, ZP-2, ZP-3).

ZP-1: present in primordal follicles.

ZP-2 and ZP-3 added to activated Follicles.

Important for filtering normal sperm and blocking polyspermy

Question 10

Tertiary Follicle

Answer 10

• Large antrum, filled with follicular fluid
• Well developed granulosa cells in the wall
• oocyte surrounded by zona pellucida, theca int/ext
• Cumulous oophorus: oocyte + granulosa cells directly around it, with a plane of weakness

At ovulation the stalk will break. so that the oocyte is free and ready for implantation out of the ovaries. The tertiary follicles push right up against the serosa of the ovary until they burst free.

Question 11

When is there endocrine control of follicular development?

Answer 11

First half (primordial-secondary): Gonadotrophin-independent growth of follicles, not controlled by FSH. We don’t clearly understand this bit! One we do know is AMH (anti-mullerian hormone)

Second Half (Antral- preovulatory):

Question 13

What happens to the follicle after the egg is released?

Answer 13

It becomes the corpus luteum (‘yellow body’) and secretes progestetone.

Corpus Luteum: cells left behind rapidly proliferate and progress, and becomes very very thick walled. Eventually becomes, less yellow, and regress into corpus albicans .

Contain lutenised granulosa and lutenised theca cells that produce Progesterone

Question 14

Function of oestrogen in the ovarian cycle

Answer 14

Upto 14 days: Decreases the levels of GnRH, FSH and LH and causes them to decrease!

Around 12 days: when oestrogen becomes too high, it switches and becomes positive feedback that stimulates the production of luteinsing hormone (which then acts on the follicles and stimulates ovulation ~12-24 hrs later)

Question 15

Inhibins function during follicular development?

Answer 15

Also produced by the granulosa cells, but negatively regulate only FSH (not LH).

Question 18

What is AMH?

Answer 18

Antimullerian hormone.

Produced in the first half of follicular development to suppress follicular recruitment and development.

The level of AMH is an indicator of ovarian development, and can be used for older-women as an indicator for fertility (not a particularly good indicator)