S4.1 The Menstrual Cycle

Question 1

Describe the ovarian cycle

Answer 1

Preparation of the gamete

Question 2

Describe the uterine cycle

Answer 2

Preparation of the endometrium

Question 3

Describe ovulation

Answer 3

Release of the gamete

Question 4

Describe gonadotropin secretion at the start of the cycle

Answer 4

Low steroid and inhibin levels, so little negative feedback so FSH increases leading to follicular development.

Question 5

Describe the secretion of gonadotrophins and gonadal steroids at the beginning of the menstrual cycle

Answer 5

FSH binds to granulosa cells and theca interna appears, allowing secretion of oestrogen and inhibin

Question 6

Describe the secretion of gonadotrophins and gonadal steroids at the mid-follicular phase

Answer 6

Oestrogen at high concentration so positive feedback on Hypo and AP

Question 7

Describe the secretion of gonadotrophins and gonadal steroids at pre-ovulation

Answer 7

Rapid increase in oestrogen and inhibin causes LH surge (FSH doesn’t rise as inhibited by inhibin). Progesterone production begins

Question 8

Describe what occurs during ovulation

Answer 8

Meiosis I completed, meiosis II starts, mature oocyte extruded through capsule of ovary

Question 9

Describe the secretion of gonadotrophins and gonadal steroids at the luteal phase

Answer 9

Follicle is luteinised by LH making the corpus luteum; secretes oestrogen, progesterone and inhibin.
LH suppressed by negative feedback due to the presence of progesterone - Waiting phase.

Question 10

Describe the secretion of gonadotrophins and gonadal steroids at the end of the cycle with no pregnancy

Answer 10

LH is suppressed so CL becomes corpus albicans and we get menses

Question 11

Describe the secretion of gonadotrophins and gonadal steroids at the end of the cycle with pregnancy

Answer 11

If fertilisation has happened the syncytiotrophoblast produces HCG which has a luteinising effect supporting CL. CL produces steroid hormones to support the pregnancy.

Question 12

What is the lifespan of the corpus luteum?

Answer 12

14 days

Question 14

What are the layers of the endometrium?

Answer 14

Functional layer is the one which sheds

Basal layer helps form the new functional layer

Question 15

Describe the endometrial changes in the uterine cycle

Answer 15

Endometrium responds to oestrogen by proliferating (glands go from straight to coiled)
Endometrium responds to oestrogen and progesterone by secreting (glands go from coiled to saw tooth)
NB myometrium doesn’t shed

Question 16

List the actions of oestrogen during the follicular phase in a non-pregnant woman

Answer 16

Thickening of endometrium
Thin alkaline cervical mucus - promotes fertilisation
Effects bone, skin and hair

Question 17

List the actions of progesterone during the luteal phase in a non-pregnant woman

Answer 17

Endometrium becomes secretory
Thick, acidic cervical mucus - limits infection as well as sperm entry
Increased body temperature

Question 18

What is the duration of the menstrual cycle?

Answer 18

21-35 days
Follicular phase varies but luteal phase is 14 days
Occurs monthly unless affected by pregnancy or low body weight

Question 19

When is pregnancy most likely to occur?

Answer 19

Within the 3 days pre-menstruation

Question 20

What is detected in the urine on a + pregnancy test?

Answer 20

HCG