Female reproductive physiology

Question 1

What is the ovarian cycle?

Answer 1

The process in which a follicle matures, the ovum is shed and the corpus luteum develops.

• Follicular phase (D1-D14)
• Luteal phase (D15-D28)

Question 2

What is the process of folliculogenesis?

Answer 2

1. Primordial follicle (single layer, squamous stromal cells)
2. Primary follicle (zona pellucida, cuboidal granulosa cells)
3. Pre-antral follicle (stratified epithelium)
4. Early antral follicle (small antrum forms, 1 dominant follicle develops past this point)
5. Antral follicle (single antrum forms)
6. Mature/Graffian/Tertiary/Pre-ovulatory follicle (oocyte completes first mitotic division)
7. Ovulation (driven by LH surge, ovum released into pertioneal cavity)
8. Corpus luteum (luteal and thecal cells)
9. Corpus albicans (fibrous tissue that is gradually reabsorbed into ovary)

Question 3

What are theca cells?

Answer 3

• Theca cells form in the connective tissue outside the granulosa cells in the pre-antral follicle
• They produce oestogen:
  
  • LH stimulates inner theca cells to produce androgens
  • FSH stimulates conversion of androgens to oestrogen via aromatase

Question 4

What is the corpus luteum?

Answer 4

• Consists of luteal and thecal cells
• Forms a fibrous clot in the ovary
• Secretes oestrogen and progesterone for ~3 months if fertilisation occurs
• Degenerates after ~10 days if fertilisation does not occur

Question 5

The dominant follicle

Answer 5

• After the early antral follicle stage, only one follicle will mature as the dominant follicle
• When the FSH levels drop, only one will survive
• This is dependent on the amount of oestrogen produced within the follicle

Question 6

Hormonal control of the ovarian cycle

Answer 6

• The overall hormonal response is controlled by GnRH pulses released by the hypothalamus

Question 7

Ovarian hormone levels throughout the cycle

Answer 7

• Oestrogen:
  
  • Peaks and D12 (middle of follicular phase)
  • Peaks at D21 (middle of luteal phase)
• Progesterone:
  
  • Peaks at D21

Question 8

Anterior pituitary hormones throughout the ovarian cycle

Answer 8

• LH surge occurs at D14 - this causes ovulation
• LH and FSH will rise towards the end of the cycle
• FSH will drop around D10 - determines the dominant follicle

Question 9

Functions of LH and FSH

Answer 9

• LH:
  
  • Induces androgen production from thecal cells
• FSH:
  
  • Pre-antral and early antral follicles continue development
  • Enlargement and multiplication of granulosa cells
  • Converts androgens (via aromatase) to oestrogen
    
    • NOTE: oestrogen negatively feeds back to the anterior pituitary to regulate production

Question 10

What does oestrogen do in the ovulatory period?

Answer 10

• In this stage, oestrogen will have a positive feedback effect on the hypothalamic-pituitary-axis
• This is responsible for the LH surge

Question 11

What happens as a result of the LH surge?

Answer 11

• It stimulates the primary oocyte to undergo first meiotic division (becomes secondary oocyte)
• Antrum size and blood flow will increase
• Enzymes and prostaglandins are secreted by granulosa cells - this breaks down follicular ovarian membrane
• Granulosa cells increase progesterone production + decrease oestrogen production
• Follicle ruptures and forms a corpus luteum

Question 12

What occurs in the luteal phase?

Answer 12

• Corpus luteum will increase levels of oestrogen and progesterone, which results in negative feedback to the anterior pituitary on FSH/LH secretion
  
  • Inhibin also limits FSH secretion
• Declining levels of FSH/LH prevents other follicles from maturing and other LH surges
• Corpus luteum degenerates in 2 weeks if no fertilisation occurs

Question 13

What is the composition of the endometrium?

Answer 13

• Stratum functionalis:
  
  • Columnar epithelium
  • Connective tissue stroma
  • Simple tubular glands
  • Spiral arteries
• Stratum basalis:
  
  • Unresponsive to ovarian hormones
  • Same vell types, more compact though

Question 14

What are the three phases of the menstrual cycle?

Answer 14

1. Menstrual cycle (D1-D5)
2. Proliferative/Pre-ovulatory cycle (D6-D14)
3. Secretory/Post-ovulatory cycle (D15-D28)

Question 15

What occurs in the menstrual phase?

Answer 15

Shedding of the endometrium occurs in this phase

Process:

1. Decrease in oestrogen/progesterone (endometrium deprived of hormonal support)
2. Increase in prostaglandin levels (spiral artery constriction, uterine contractions)
3. Ischaemic endometrial cells die
4. Spiral arterioles dilate to cause haemorrhaging
5. Stratum functionalis sloughs off

Question 16

What occurs in the proliferative/pre-ovulatory phase?

Answer 16

• The stratum functionalis is rebuilt - long, straight glands with absence of secretory products
• Proliferation of glandular epithelial cells, stroma and blood vessels + gland enlargement
• Increase in plasma oestrogen:
  
  • Promotes progesterone receptor expression on endometrial cells
  • Thins cervical mucous
• Ovulation marks end of this phase

Question 17

What occurs in the secretory/pre-ovulatory phase?

Answer 17

• This prepares the endometrium for implantation of a fertilised egg
• Driven by oestrogen and progesterone - the rapid increase in progesterone causes:
  
  • Thickening of cervical mucous
  • Inhibition of prostaglandin-induced contractions of the myometrium
• Glands and stroma enlarge
• If there is no fertilisation:
  
  • No progesterone -> artery spasms -> decreased O2 levels -> blood enters fragmented capillaries -> menses begins again

Question 18

What is the histology of the endometrium during the secretory phase?

Answer 18

• Saw-toothed and coiled glands with secrety products present
• Abundant blood vessels in the stroma
• Endometrium twice as thick