*E1 Human Physiology - Hormonal control of reproductive cycle

Question 1

Interaction of hormones in the menstrual cycle

Answer 1

Day 1 - 5
- Uterine lining breaks down, menstruation starts
- Hypothalamus secretes GnRH to stimulate the pituitary gland to secrete FSH and LH
- (1) FSH stimulates the development of follicles inside the ovary
- (2) FSH stimulates the developing follicles to secrete oestrogen

Day 5 - 11
- (3) Oestrogen stimulates the thickening of uterine lining to prepare for the implantation of embryo
- (4) Increase in oestrogen level exerts negative feedback by inhibiting further pituitary secretion of FSH, to prevent the ovary to develop another mature follicle
- (5) Negative feedback is converted to positive feedback shortly before ovulation to trigger sudden surge of LH and FSH

Day 14 (Ovulation)
- (6) LSH reaches the peak. A high level of LH and FSH triggers ovulation

Day 14 - 28
- (7) High level of LH stimulates the ruptured follicle to develop into yellow body
- (8) High level of LH stimulates the yellow body to secrete progesterone and oestrogen
- (9) Progesterone and oestrogen maintains the thickness of uterine lining to prepare for the implantation of embryo
- (10) High levels of progesterone and oestrogen inhibit the pituitary gland to secrete FSH and LH to ensure no more follicles will keep on developing and release another mature ovum

No fertilization:
- The yellow body degenerates and stops secreting progesterone and oestrogen, a low level of progesterone and oestrogen cause the breakdown of the thickened uterine lining, menstruation occurs
- The low level of progesterone and oestrogen remove the negative feedback on pituitary gland, which will secrete FSH again

Successful fertilization:
- If there is successful fertilization and subsequent implantation of embryo, the embryo will secrete HCG, which prevents the degeneration of yellow body
- The yellow body will secrete and keep progesterone and oestrogen at high level. This helps maintain the thickness of uterine lining

Question 2

Contraceptive pills

Answer 2

Principle:
- High level of progesterone inhibits the secretion of FSH and LH from the pituitary gland
- The low level of FSH is not sufficient to stimulate follicle development
- The low level of LH is not sufficient to stimulate ovulation
- No fertilization takes place

• Synthetic progesterone and oestrogen can resist the destructive action of liver and they can be metabolized slowly in the body
• Taking a pill with hormones daily for 21 days + taking a pill without hormones for another 7 days to allow the fall of oestrogen and progesterone level so that menstruation can take place

Question 3

Vaginal ring

Answer 3

Advantage
- Effectiveness of rings is not affected if the female has problems in digestive system as the hormones are not absorbed through the digestive tract

Disadvantage
- May be infected easily

Question 4

In vitro fertilization

Answer 4

• Injection of hormone to woman to stimulate her ovaries to form a large number of mature ova for collection and used in IVF
• Semen of male is collected without the need of hormonal stimulation before since one ejaculation contains millions of sperms
• Semen and eggs are mixed in a suitable culture medium in petri dish
• Fertilized eggs are cultured for several days until they develop to embryos to ensure the embryo formed is developing normally and ready for implantation
• Six embryos were put into the uterus since some embryos might fail to implant into the uterine lining
• IVF is completed