Control of menstrual cycle (BIOL5)

Question 1

The menstural cycle involves…

Answer 1

• A follicle developing in ovary
• Ovulation - egg released
• Uterus lining becoming thicker, so fertilised egg can implant
• Corpus luteum developing from remains of follicle

Question 2

The hormones controlling the menstrual cycle involve…

Answer 2

• FSH:
  
  • stimulate follicle to develop
• LH:
  
  • stimulates ovulation/corpus luteum to develop
• Oestrogen:
  
  • stimulates uterus lining to thicken
• Progesterone:
  
  • maintains thick uterus lining

Question 3

Where are the hormones controlling the menstural cycle secreted from?

Answer 3

FSH and LH secreted by anterior pituitary gland

Oestrogen and progesterone secreted by ovaries

Question 4

Negative feedback in controlling hormone levels (FSH)

Answer 4

• FSH stimulates ovary release of oestrogen
• Oestrogen inhibits release of FSH
• After FSH stimulated, negative feedback keeps FSH conc low

Question 5

Negative feedback in controlling hormone levels (LH)

Answer 5

• LH stimulates corpus luteum to develop, producing progesterone
• Progesterone inhibits release of LH
• Negative feedback ensures that no more follicles develop

Question 6

Positive feedback in controlling hormone level (Oestrogen)

Answer 6

• Oestrogen stimulates pituitary to release LH
• LH stimulates ovary to release oestrogen
• Oestrogen stimulates pituitary to release LH
• H. oestrogen conc triggers positive feedback

Question 7

1) High FSH concentration in blood…

Answer 7

• FSH stimulates follicle development
• Follicle releases oestrogen
• FSH stimulates ovaries to release oestrogen

Question 8

2) Rising concentration of oestrogen…

Answer 8

• Oestrogen stimulates uterus lining to thicken
• Oestrogen inhibits FSH being released from pituitary gland

Question 9

3) Oestrogen concentration peaks…

Answer 9

• H. oestrogen conc stimulates release LH/FSH

Question 10

4) LH surge (rapid inc)…

Answer 10

• Ovulation stimulated by LH - follicle ruptures and egg released
• LH stimulates ruptured follicile to turn into corpus luteum
• Corpus luteum releases progesterone

Question 11

5) Rising concentrations of progesterone

Answer 11

• Progesterone inhibits FSH and LH release from pituitary
• Uterus lining maintained by progesterone
• If no embryo implants, corpus luteum b/d and stop releasing progesterone

Question 12

6) Falling concentration of progesterone…

Answer 12

• FSH and LH concentrations inc. as they’re not inhibited by progresterone
• Uterus lining not maintained - b/d - menstruation occurs and cycle again!