Physiology

Question 1

Does dopamine stimulate or inhibit prolactin?

Answer 1

Inhibit

Question 2

Draw the menstrual cycle graph (5)

Answer 2

See picture 11

Question 3

Name the 4 phases of the menstrual cycle

Answer 3

• Follicular: day 1→ ovulation. Average 14 days. Oogenesis + selection dominant follicle.
• ovulation
• luteal phase: average 4 days
• menstruation

Question 4

Name and describe the 3 phases of the uterine cycle

Answer 4

• Proliferative phase: estrogenic/post menstrual phase. Corresponds to follicular phase
• Secretary: corresponds to luteal phase. Progestational / premenstrual phase. increased progesterone → endometrial glands proliferate in corkscrew-like fashionwith dilated capillaries
• ischaemic: decline in oestrogen and progesterone → endometrial degradation

Question 5

Describe the follicular phase of the menstrual cycle (10)

Answer 5

Oogenesis

• Starts at 6-8 weeks gestation as foetus: mitotic division of germ cells → oogonia, reach max 6-7 million at 16 - 20 weeks gestation
• Oogonia undergo mitosis that arrest in prophase 1 → form about 1-2 million primary oocytes present at birth. Primary oocytes decrease to 300 000 - 400 ooo at puberty of which 500 will mature.
• puberty: meiosis of primary oocyte resume before each menstrual cycle and completed just before ovulation.
• second meiotic division when sperm penetrates → single mature ovum and 3 polar bodies.

Selection dominant follicle

• FSH cause follicular growth
• as they grow, estradiol = major component of follicular fluid
• granulosa cells af follicles secrete inhibin a → marker of follicular growth
• these 2 cause negative feedback to pituitary to suppress FSH
• survival of follicle depends on its ability to convert an androgen dominant environment into aestrogen. Dominant follicle has more FSH receptors + high intra follicular estradiol,.
• withdrawal FSH → pituitary initiate surge in lh. To respond to lh surge, granulosa cells must acquire lh receptors so FSH changes its focus of action to upregulate lh receptors

Question 6

Describe the ovulation phase of the menstrual cycle (6)

Answer 6

• Release ovum from dominant follicle of ovary within 36 hours from onset of LH surge (usually around 3:00, can be detected in urine later that evening) and estradiol peak , and 10-12 hours after lh peak..
• lh surge cause
  → resume meiosis and maturation of oocyte,
  → luteinisation of granulosa cells
  → progesterone production
  → increase prostaglandin production to disrupt follicular wall to enable ovulation
• progesterone terminate surge by negative feedback

Question 7

Describe the luteal phase of the menstrual cycle (5)

Answer 7

• After ovulation, leutinisation of granulosa cells and formation corpus luteum take place
• upregulation of lh receptors on granulosa cells during follicular phase is important in maintaining corpus luteum , so lifespan of corpus luteum (Approx 14 days) depends on lh secretion.
• large cells of corpus luteum = steroidogenesis: produce high amount progesterone, moderate amount estradiol + inhibin A.
• small cells = contain lh and HCG receptors which potentiaTe function of large cells.
• if no fertilisation and implantation within 14 days from ovulation, no production HCG → corpus luteum becomes atretic and stops producing progesterone, regresses. Endometrial lining sheds. Rise in Gonadotrophins due to no inhibition → cycle starts again

Question 8

Earliest detection bhcg?

Answer 8

6-12 days after ovulation

Question 9

At what rate does bhcg increase after implantation of a viable intrauterine pregnancy?

Answer 9

Doubles every 29 - 53 hours in first 30 days after implantation