The Menstrual Cycle

Question 1

What are the 2 different stages of the menstrual cycle?

Answer 1

• The ovarian cycle
• The uterine cycle

Question 2

What is endometriosis and how can it be treated?

Answer 2

A condition where endometrial tissue can appear ectopically causing pain

Treatment: continous GnRH desensitises GnRH receptors to switch of HPG axis and alleviate symptoms

Question 3

Describe what happens in the follicular phase of the ovarian cycle

Answer 3

• FSH levels start to rise as there is little inhibition
• FSH causes number of granulosa cells to increase, theca interna & externa develop and follicles start producing oestrogen
• Low level oestrogen →negative feedback on HPG
• As follicle develops oestrogen levels rise → positive feedback causes LH to rise
• inhibin rises to prevent FSH stimulating more than 1 dominant follicle

Question 4

A rise in which hormone causes ovulation

Answer 4

LH- known as LH surge

Question 5

What causes the LH surge?

Answer 5

In preparation for ovulation, high oestrodial levels enhance the sensitivity of the anterior pituitary to GnRH → more LH released

Question 6

What happens to hormone levels after ovulation?

Answer 6

• Follicle is leutenised → secretes oestrogen and large amounts of progesterone
• Inhibin is produced by corpus luteum
• LH suppressed from negative feedback effect of oestrogen & progesterone
• Effect = axis turned off and a waiting phase established

Question 7

What is the lifespan of the corpus leuteum if not fertilised?

Answer 7

14 days

Question 8

If fertilisation does not occur, what happens to the corpus luteum and what effect does this have on hormone levels?

Answer 8

Corpus luteum degrades

Causes a drop in inhibin, oestrogen & progesterone

Allows the cycle to start again

Question 9

What are the 2 phases of the uterine cycle?

Answer 9

1. Proliferative phase
2. Secretory phase

Question 10

Which layer of the endometrium is shed during menstruation?

Answer 10

The Functional layer

The basal layer remains

Question 11

How does the endometrium change throughout the menstrual cycle?

Answer 11

Early proliferative: glands are sparse and straight

Late proliferative: Glands become coiled and functional layer doubles in size

Early secretory: once ovulation occurs, endometrium at maximal thickness. Coiled glands are very pronounced

Late secretory: Saw tooth like appearance as hormones from corpus luteum fall

Question 12

What happens to the HPG axis if fertilisation occurs?

Answer 12

• Embryonic tissue (syncytiotrophoblast) secretes hCG (human chorionic gonadotrophin)
• hCG has the same function as LH and maintains the corpus luteum
• Oestrogen and progesterone continued to be produced

Question 13

What are the functions of oestrogen in the luteal phase in promoting fertilsation?

Answer 13

• Proliferates endometrium
• Proliferates myometrium
• Fallopian tube motility
• Produced thin, alkaline cervical mucus

Question 14

What are the functions of progesterone in the luteal phase to maintain a viable pregnancy?

Answer 14

• Thicken endometrium into secretory form
• Reduced motility of myometrium
• Thick, acidic cervical mucus prevents further entry of sperm

Question 15

What is the normal duration of the menstrual cyle?

Answer 15

Between 21-35 days