Physiology of Menstrual Cycle

Question 1

What does GnRH stimulate the release of? Describe the release of GnRH

Answer 1

Pulsatile relesae
Stimulates FSH first
from anterior poster

Question 2

Compare the roles of FSH vs LH

Answer 2

FSH - actually stimulates around 15-20 follicles

LH - main job is to stimulation OVULATION by acting on theca cells

Question 3

What does FSH do? What does it stimulate?

Answer 3

FSH stimulates PRIMORDIAL FOLLICLES to develop. The granulosa cells surrounding the follicles start to grow.

The granulosa cells release oestrogen.

Question 4

What secretes oestrogen?

Answer 4

Granulosa cells - following stimulation from FSH

Question 5

What is the role of oestrogen?

Answer 5

• Breast tissue development
• Blood vessels in uterus and endometrium grow
• Cervical mucus becomes thinner to allow sperm to go through
• negative feedback on GnRH, FSH and LH

Question 6

What happens just before day 14?

Answer 6

The follicle gets ready to release the ovum. A dip in oestrogen from the granulosa cells means that there is disinhibition, so there is a surge in LH, which releases the ovum.

Question 7

What happens to the remainder of the follicle when the ovum is released?

Answer 7

It becomes a corpus luteum which produces PROGESTERONE.

Question 8

Function of progesterone

Answer 8

Acts on tissues which have previously been stimulated by oestrogen.

For example,
it thickens and maintains the endometrium.

Thickens cervical mucus to prevent further pregnancy.

Rises body temp.

Question 9

What maintains the corpus luteum?

Answer 9

HCG from the baby - this ensures that the corpus luteum keeps producing progesterone and oestrogen

Question 10

What causes menstruation to begin again?

Answer 10

If HCG isn’t produced, then the corpus luteum degenerates. So the drop in progesterone and oestrogen causes lack of negative feedback on LH and FSH so the cycle of menstruation starts up again

Question 11

What is the difference between the corpus luteum and the follicles in the ovaries?

Answer 11

Corpus luteum can produce both prog and oestrogen, whereas the follicles only really produce oestrogen.

Question 12

Summarise the hormonal graph in the menstrual cycle

Answer 12

GnRH is released in a pulsatile manner from the hypothalamus.

This stimulates FSH release from the anterior pituiatry. Thus FSH is released during the follicular phase of the menstrual cycle. This prompts the developing follicles to release oestrogen fro the granulosa cells. These have a negative feedback on LH and FSH.

Before day 14, there is a drop in oestrogen, which results in a rise in the level of LH.

This LH surge causes OVULATION and a corpus luteum to be formed, creating the luteal phase.

This corpus luteum produces BOTH oestrogen and PROGESTERONE.

The progesterone maintains the lining of the endometrium.

If no HCG is released from a fertilised egg, then the corpus luteum breaks down, so the levels of oestrogen and progesterone drop. This means the endometrium isn’t maintained, so you get a period.

This drop also results in a lack of negative feedback on LH and FSH, so the cycle starts again.

Question 13

How do we check for ovulation?

Answer 13

Day 21 progesterone - released from the corpus luteum if an egg has been released.

If a woman has more than a 28 day cycle, check 7 days minus their cycle length.

Question 14

What does HCG stand for?

Answer 14

Human chorionic gonadotrophin

Question 15

What maintains the corpus luteum?

Answer 15

beta HCG

Question 16

What takes over the production of progesterone from the corpus lutuem?

Answer 16

Placenta around 5-10 weeks

Question 17

Summary of hormones and where they are produced

Answer 17

GnRH - hypothalamus
FSH/LH - anterior pituitary
Oestrogen - granulosa cells
Progesterone and oestrogen - corpus luteum
Beta HCG - embryo