5: Menstrual Cycle

Question 1

Name 4 hormones
Where are they released from?
What is their target organ/s?

Answer 1

Follicle-stimulating hormone from pituitary gland acts on follicles
Luteinising hormone from pituitary gland, acts on ovaries
Oestrogen from ovaries, acts on uterus lining and pituitary gland
Progesterone from corpus luteum, acts on uterus lining and pituitary gland

Question 2

Give an example of positive feedback in the menstrual cycle

Answer 2

Oestrogen stimulates the release of LH
LH stimulates the ovary to release more oestrogen
Oestrogen further stimulates the release of LH, and so on
High oestrogen concentration triggers postive feedback to make ovulation happen

Question 3

Give examples of negative feedback in the menstrual cycle

Answer 3

• FSH stimulates the ovary to release oestrogen, oestrogen inhibits further release of FSH
  After FSH has stimulated follicle development, negative feedback keeps the FSH conc low so that no more follicles develop
• LG stimulates the corpus luteum to develop, which produces progesterone. Progesterone inhibits further release of LH
  Negative feedback makes sure that no more follicles develop hone the corpus lute is developing. it also makes sure the futures lining isn’t maintained if no embryo implants.

Question 4

What is the role of each of the 4 hormones?

Answer 4

FSH - stimulates a follicle to develop
LH - stimulates ovulation and corpus luteum development
Oestrogen - stimulates the uterus lining to thicken
Progesterone - maintains the thick uterus lining, ready fro implantation of an embryo

Question 5

Describe 6 stages of the menstrual cycle

Answer 5

1. FSH stimulates follicle development, follicle releases oestrogen.
2. Oestrogen thickens uterus lining, inhibits FSH
3. High oestrogen stimulates release of LH and FSH
4. Ovulation stimulated by LH, LH turns follicle into corpus luteum, this releases progesterone
5. Progesterone inhibits FSH and LH, uterus lining maintained, no embryo = corpus luteum breaks down, less progesterone
6. FSH and LH no longer inhibited, and lining is not maintained, uterus lining breaks down

Question 6

Explain how negative feedback ensures only one main follicle develops

Answer 6

FSH stimulates a follicle to develop. Developing follicle releases oestrogen and FSH stimulates follicles to release oestrogen. Oestrogen inhibits the release of FSH so no more follicles are stimulated to develop

Question 7

Explain how positive feedback is involved in ovulation

Answer 7

High oestrogen concentration stimulates the anterior pituitary to release LH. LH stimulates the ovary to release more oestrogen, which further stimulates the anterior pituitary in a positive feedback loop

Question 8

The contraceptive pill containers oestrogen and progesterone. Suggest how taking the pill can prevent pregnancy

Answer 8

Oestrogen and progesteron inhibit FSH. Because there’s no FSH, the follicle isn’t stimulated to develop, so there is no ovulation