Menstrual cycle

Question 1

What is the super top master hormone in the menstrual cycle?

Answer 1

GnRH, released in a pulsatile manner from the hypothalamus into the portal vessels, binding onto receptors on gonadotrope cells in the anterior pituitary gland.

Question 2

What does GnRH do?

Answer 2

Drives LH and FSH secretion in a pulsatile manner
Changing the pulsality of GnRH changes LH and FSH secretion from anterior pituitary

Slow pulsing = FSH release

Fast pulsing = LH release

Question 3

What is the menstrual cycle?

Answer 3

A cycle of changes in females involving the hypothalamus, pituitary, ovaries and uterus that prepares a secondary oocyte for fertilisation

Question 4

What drives the menstrual cycle?

Answer 4

GnRH, FSH, LH, oestrogen, progesterone

Question 5

How long is the menstrual cycle?

Answer 5

28-32 days, begins on day 1 of menstruation

Two stages of 14 days with ovulation in the middle

Question 6

How do GnRH, LH and FSH interact?

Answer 6

GnRH neurons in hypothalamus generate pulsatile GnRH release.

FSH & LH act vie endogenous opioids in the hypothalamus to modulate the frequency and amplitude of these pulses

Amplitude and frequency of GnRH pulsality dictates pattern of LH and FSH

Question 7

What does LH primarily do?

Answer 7

androsterone production in theca cells

Question 8

FSH’s main effect?

Answer 8

oestrogen production in granulosa cell and follicle growth

Question 9

1st half of menstrual cycle

Answer 9

Day 1-14
Menstruation to ovulation
Ovaries in follicular phase
Endometrium in menstrual and proliferative phases

Question 10

What is the follicular phase?

Answer 10

Development of the preantal follicle into the antal follicle into the Graafian follicle to prepare for ovulation

Question 11

Hormone changes in the follicular phase?

Answer 11

During menstruation:
LH and FSH rise as oestrogen and progesterone decrease

FSH stimulates antral follicles to mature

Granulosa and theca cells make oestrogen, which rises exponentially over the first 12 days.

Oestrogen stimulate LH receptor growth in granulosa cells -> LH surge

LH surge -> one follicle (dominant follicle) released, others regress

Question 12

What does the dominant follicle contain?

Answer 12

Primary oocyte - female gamete
Zona pellucida - glycoprotein layer surrounding oocyte (egg shell)
Granulosa cells- cuboidal cells surrounding oocyte, secrete oestrogens
Antrum - fluid filled cavity within granulosa cells
Basement membrane/lamina
Theca interna - androgen-secreting stromal cells
Theca externa - non-secretory stromal cells

Question 13

Endometrial changes in the menstrual phase of 1st half of cycle?

Answer 13

Days 1-4
Loss of functional layer of endometrium which is ischaemic and necrotic
Sloughed tissue passes through vagina with blood from degenerating spiral arteries

Question 14

Endometrial changes in proliferative phase of 1st half of cycle?

Answer 14

Rising oestrogen levels cause:

• proliferation of cells in the basal layer of the endometrium to form a new functional layer. Glands are formed but not yet active
• Secretion of a watery cervical mucous to facilitate sperm transport across the cervix.

Question 15

What is ovulation?

Answer 15

Expulsion of the oocyte (with the zona pellucida and some granulosa cells) from the Graafian corpuscle into the peritoneal cavity. It is then wafted by cilia of the fimbriae into the fallopian tubes.

Question 16

What hormonal changes cause ovulation?

Answer 16

The dominant antral follicle secreting loads of oestrogen so that negative feedback turns positive and there is a DRAMATIC LH SURGE (kweeen) (also FSH to a lesser extent).

LH surge causes follicle to complete first meiotic division and rupture.

Question 17

2nd half of menstrual cycle

Answer 17

Day 14-28
Ovulation to menstruation
Length determined by lifespan of corpus luteum

Question 18

Luteal stage of menstrual cycle?

Answer 18

Follicle becomes a corupus luteum

LH surge continues acting on the granulosa and theca cells in the empty follicle after ovulation, and cells change and become yellow to become lutein cells.

Ruptured follicle rump is called corpus luteum.

Over next 10 days, corpus luteum secretes high levels of PROGESTERONE and oestrogen, inhibiting LH and FSH release.

Then low LH causes corpus luteum to spontaneously involute and lose secretory ability, becoming the corpus albicans

Question 19

What are the effects of the hormones secreted by the corpus luteum?

Answer 19

The corpus luteum secretes progesterone and oestrogen

These inhibit LH and FSH release from the pituitary gland

Falling LH can’t maintain the corpus luteum so undergoes involution

involution makes progesterone and oestrogen levels decrease dramatically, so loss of negative feedback to pituitary gland

FSH and LH secretion increases, causing ovarian follicle growth, thus starting the next cycle.

Question 20

Endometrial changes during second phase of menstrual cycle?

Answer 20

Secretory phase
After ovulation, progesterone from corpus luteum stimulates differentiation in the endometrium

Nutrients are stored in the cells
Glands become tortuous in preparation for secretion

Endometrial glands start to secrete glycogen-rich secretion

In absence of progesterone following involution of corpus luteum, spiral arteries begin to coil and constrict, becoming ischaemic and necrotic. Blood leaks from capillaries and functional endometrium is shed -> menstruation, start of next cycle.

Question 21

What happens if fertilisation occurs?

Answer 21

hCG released from implanting conceptus which binds to LH receptors on luteal cells so that the corpus luteum doesn’t involute.

Question 22

Cervical changes during menstrual cycle?

Answer 22

Watery cervical mucous during ovulation to aid sperm swimming through cervix
Cervical os dilates around ovulation and menstruation

Oestrogen thins cervical mucous
Progesterone thickens cervical mucous