Control of the Menstrual Cycle

Question 1

What does the menstrual cycle involve?

Answer 1

• A follicle developing in the ovary
• Ovulation
• The uterus lining becoming thicker so a fertilised egg can develop
• A structure called a corpus luteum developing from the remains of the follicle.

Question 2

What happens if fertilisation does not occur?

Answer 2

The uterus lining breaks down and leaves the body through the vagina. This is known as menstruation , which marks the end of one cycle and the start of another.

Question 3

Name the four hormones involved with the menstrual cycle and explain what they do.

Answer 3

• Follicle Stimulating Hormone (FSH) - stimulates the follicle to develop
• Luteinising Hormone (LH) - stimulates ovulation and stimulates corpus luteum to develop
• Oestrogen - stimulates uterus lining to thicken
• Progesterone - maintains the thick uterus lining, ready for implantation of an embryo

Question 4

Where are the hormones secreted from?

Answer 4

FSH and LH are secreted from Pituitary Gland in the brain.

Oestrogen and Progesterone are secreted from ovaries

Question 5

What happens during stage 1 of the menstrual cycle?

Answer 5

High concentration of FSH in the blood stimulates follicle development.
FSH stimulates ovaries to release oestrogen so concentration of oestrogen in the blood rises which stimulates uterus lining to thicken.
Oestrogen inhibits FSH being released from the anterior pituitary gland.

Question 6

What happens during stage 2 of the menstrual cycle?

Answer 6

Oestrogen concentration rises to a high level which no longer inhibits release of FSH.
High level of oestrogen stimulates release of LH and FSH.
LH stimulates ovaries to release more oestrogen.
As more oestrogen is released, pituitary gland is stimulates to release more LH.
There is a surge in LH concentration which stimulates ovulation - the follicle ruptures and the egg is released.
LH also stimulates ruptured follicle to turn into a corpus luteum.

Question 7

What happens during stage 3 of the menstrual cycle?

Answer 7

The corpus luteum releases progesterone, so concentration rises.
Progesterone inhibits release of FSH and LH so these concentrations fall.
The uterus lining is maintained by progesterone.

Question 8

What happens is no embryo implants?

Answer 8

The corpus luteum breaks down and stops releasing progesterone. When progesterone stops being released, FSH and LH concentrations increase as they are no longer being inhibited.
The uterus lining isn’t maintained so it breaks down - menstruation occurs and the cycle repeats.

Question 9

What feedback mechanisms occur and how do they work.

Answer 9

Stage 1 - negative feedback - maintains a low FSH concentration so no more follicles develop
Stage 2 - positive feedback - high oestrogen concentration continually triggers release of LH
Stage 3 - negative feedback - ensures no more follicles develop while the corpus luteum is developing.