Female reproduction and folliculogenesis

Question 1

What is the general anatomy of the female reproductive tract?

Answer 1

1. Vagina
2. Cervix
3. Uterus
4. Oviduct
5. Ovary

Question 2

What are the three functions of the ovary?

Answer 2

Folliculogenesis
Oogenesis
Hormone production

Question 3

What are the ovarian hormones?

Answer 3

Androgen (androstendione) - theca cells
Oestrogen - granulosa cells
Progesterone - Luteal cells

Question 4

What is the hormone dependant cycle?

Answer 4

Follicular phase before oocyte release at ovulation

Luteal phase after ovulation

Question 5

What is the hypothalamic - pituitary - gonadal axis?

Answer 5

→Hypothalamus←
                       ↓ GnRH
  -     →  Anterior pituitary ←      +
                       ↓ LH/FSH
             ←   Ovary   →

Question 6

What is oestrogen’s role?

Answer 6

17b-oestradiol
Oestrone
- induce secondary sexual characteristics
- prepare uterus for sperm transport
- stimulate growth and activity of mammary gland and endometrium
- regulate secretion of gonadotrophins (FSH,LH)

Question 7

What is progesterone’s role?

Answer 7

17a - hydroxy - progesterone
20a - hydroxy - progesterone
- prepare uterus to receive embryo
- maintain uterus during pregnancy
- stimulate growth of mammary glands but suppress secretion of milk
- regulate secretion of gonadotrophins (LH/FSH)

Question 8

What is the structure of the ovarian follicle?

Answer 8

From the theca (connective tissue)in:

• theca
• granulosa cells
• follicular cavity
• zona pellucida
• oocyte

Question 9

What is the ovarian follicle?

Answer 9

Functional unit of the ovary
Contains hormone producing cells theca and granulosa
Female mammals are born with a fixed number of primordial follicles

Question 10

What is folliculogenesis?

Answer 10

Follicle growth

- occurs in follicular phase

Question 11

What is the primordial follicle?

Answer 11

1 primary oocyte and 1 layer of pre-granulosa cells

Question 12

What is the primary follicle?

Answer 12

Increased oocyte size

• Oocyte
• 1 layer of cuboidal granulosa cells - these become oestrogen producing cells in response to FSH
• Zona Pellucida separates oocyte from granulosa cells
• Granulosa cells have FSh receptors but are gonadotrophin - independent at this stage

Question 13

What is the secondary follicle?

Answer 13

Multiple layers of granulosa cells
Oocyte fully grown
Theca cells form and differentiate into:
- theca interna
- theca externa
Theca cells produce androgens in response to LH
Vascularisation starts to occur
Gonadotrophins LH + FSH can now access the follicle via the blood

Question 14

What are the tertiary follicles?

Answer 14

Granulosa cells secrete fluid - antrum forms
Pituitary LH induces theca cells to become steriodogenic = produce androgen androstenedione - acts as a substrate for oestrogen synthesis by granulosa cells
Pituitary FSH induces granulosa cell proliferation - futher stimulating oestrogen production

Question 15

What is the graafian follicle?

Answer 15

Single follicle is selected to form a dominant follicle - due to competition for FSH

• dominant mature follicle is the graafian follicle
• remaining follicles degenerate - follicle atresia (narrowing)

Question 16

What is the structure of the graafian follicle? (from theca interna inwards)

Answer 16

• theca interna
• basement membrane
• membrane granulosa with oocyte
• antrum

Question 17

How are the graafian follicles involved in hormonal control?

Answer 17

Oestrogen levels are high which stimulates LH and FSH production by the pituitary gland and expression of LH on theca cells
Increased levels of androgen are converted to oestrogen by increased numbers of granulosa cells which results in even higher oestrogen levels and further stimulation of LH and FSH
- positive feedback loop

Question 18

How are the graafian follicles involved in ovulation?

Answer 18

Extremely high levels of oestrogen induce LH surge which induces secretion of proteolytic enzymes which weaken follicle wall
- lysosomal enzymes
- collagenase
LH surge increased blood flow to ovary which increases follicular wall pressure
- increased fluid accumulation in follicle antrum
Follicle wall ruptures = stigma and the oocyte is released from oocyte

Question 19

What is ovulation?

Answer 19

Fimbriae of oviduct search for follicle ready to rupture an ovary
Fluid filled follicle on ovary and fimbriae ready to collect oocyte

Question 20

How do horse ovaries ovulate?

Answer 20

Ovulation happens at the ovulation fossa on the inner curvature of the ovary. Because ovulation happens internally, corpora lutea are not palpable in the mare. Instead, a misshapen ovary is usually indicative of a growing follicle.

Question 21

Describe the structure of the oocyte? from outside in

Answer 21

Zona pellucida 
Cumulus cells 
- both outside 
Perivitelline space 
Polar body 
- on surface 
Oocyte cytoplasm
- inside

Question 22

What is the corpus luteum?

Answer 22

After ovulation the ovary enters the luteal phase of its cycle
- rapid invasion of blood vessels to form corpus hemorrhagium
- Pituitary LH causes luentisation of remaining granulosa and theca cells
New luteal cells produce progesterone

Question 23

What is luteal regression in sheep?

Answer 23

Corpus luteum remains for either:
- duration of luteal phase of ovarian cycle
- early pregnancy
If no pregnancy, corpus luteum must regress at the end of the luteal phase
Prostaglandin F2𝛂 secreted by uterus 10-15 days after CL formation
CL breaks down
Ovary begins new follicular phase

Question 24

What is the oestrus cycle?

Answer 24

• external marker standing behaviour (oestrus)

- animals who only exhibit receptivity to mating at ovulation

Question 25

What is the menstrual cycle?

Answer 25

• external marker is menstruation

- humans who exhibit mating behaviour throughout the ovarian cycle

Question 26

What do the oestrus and menstrual cycles consist of?

Answer 26

Luteal phase

Follicular phase

Question 27

What can the oestrus cycle be characterised by?

Answer 27

Hormones secreted by the ovary
- follicular phase = oestrogen dominant
- luteal phase = progesterone dominant
Receptivity to mating
Reflected in vaginal cytology
- pro-oestrus = period immediately before mating behaviour is observed - oestrogen dominant
- oestrus = receptive to mating - oestrogen dominant
- metoestrus = transitional period
- dioestrus = pseudo-pregnancy - progesterone dominant
- anoestrus = ovarian cycle rests in seasonal breeders

Question 28

What is the relationship between the secretion of ovarian hormones?

Answer 28

If one is released the other one is suppressed