Menstrual Cycle

Question 1

What are the two phases of the ovarian cycle?

Answer 1

Follicular

• first 14 days
• from growth of follicles in ovaries to release of oocyte

Luteal

• second 14 days
• from release of follicle to formation and degeneration of corpus luteum

Question 2

What are the two phases of the uterine cycle?

Answer 2

Proliferative phase

• first 14 days
• thickness of endometrium rapidly increaes
• influenced by FSH and oestrogen

Secretory phase

• endometrial lining becomes highly vascular and oedematus
• influenced by progesterone

Question 3

What is the difference between the ovarian and the uterine cycles?

Answer 3

• both 28 day cycles divided into two 14 day components (with the release of an ovarian follicle separating the two phases)
• ovarian cycle: follicular and luteal phases; key events are the maturation and release of a follicle, then the formation and degeneration of a corpus luteum
• driven by FSH and oestrogen
• uterine cycle: proliferative and secretory phases; key events are the thickening of the endometrial lining; then the vascularization and oedematization of the endometrial lining
• driven by progesterone

Question 4

What happens in the ovarian cycle?

Answer 4

1. Follicular phase (first 14 days)
   - FSH stimulates selection and maturation of a dominant follicle (from 12-20 primary follicles)
   - dominant follicle grows an oocyte
   - dominant follicle produces oestrogen (from granulosa cells), which triggers a surge of LH
   - LH causes a growth spurt for follicle and triggers ovulation
2. Ovulation (mid-point)
   - oocyte is ejected from dominant follicle
   - fimbrae of fallopian tubes pick up oocyte
3. Luteal (last 14 days)
   - dominant follicle transforms into corpus luteum
   - corpus luteum secretes progesterone to prepare endometrium for implantation of fertilized oocyte (thickens & vascularizes)
   - corpus luteum degenerates

Question 5

What happens in the uterine cycle?

Answer 5

1. Proliferative phase:
   - oestrogen produced by dominant follicle triggers stem cells in basal layer to generate a new functional layer of uterine endothelium
2. Secretory phase:
   - corpus luteum releases progesterone, which converts functional layer into secretory mucosa
   - when corpus luteum degenerates, progesterone levels decline, spiral arteries spasm and ischaemic endometrial cells undergo necrosis and slough off

Question 6

What causes the sloughing off of the endometrial layer of the uterus if a pregnancy does not occur in a menstrual cycle?

Answer 6

• if pregnancy does not occur, corpus luteum degenerates and progesterone levels decline
• spiral arteries supplying endometrium of uterus spasm and cause ischaemia of endometrium
• functional layer of endometrium sloughs off
• in the proliferative phase of the next menstrual cycle, the stem cells in the basal layer of the endometrium will regenerate a new functional layer

Question 7

What is the luteal phase?

Answer 7

• the second half of the ovarian cycle
• the corpus luteum degenerates and progesterone levels decline
• causes spiral arteries to spasm, causing ischaemia of the endometrium
• functional layer of endometrium sheds in menstrual bleeding

Question 8

What is the follicular phase?

Answer 8

• the first half of the ovarian cycle
• FSH stimulates selection and maturation of a dominant follicle
• granulosa cells of dominant follicle release oestrogen
• oestrogen triggers LH release
• LH triggers growth spurt of dominant follicle and triggers ovulation

Question 9

Which hormone triggers ovulation?

Answer 9

• oestrogen is released by granulosa cells of dominant follicle, and triggers LH release
• LH triggers ovulation, and converts ruptured follicle into corpus luteum

Question 10

What are the actions of FSH in the menstrual cycle?

Answer 10

• released by anterior pituitary gland in response to GnRH from the hypothalamus
• triggers follicular phase of ovarian cycle
  (selection and maturation of dominant follicle)

Question 11

What are the actions of oestrogen in the menstrual cycle?

Answer 11

• oestrogen is produced by the granulosa cells of the dominant follicle in the follicular phase of the ovarian cycle
• oestrogen triggers the release of LH from the anterior pituitary gland
• LH causes a growth spurt for the dominant follicle and triggers ovulation, then converts ruptured follicle into corpus luteum

Question 12

What are the actions of LH in the menstrual cycle?

Answer 12

• LH is produced by the anterior pituitary gland in response to GnRH from the hypothalamus
• triggers ovulation and converts ruptured follicle into corpus luteum

Question 13

What is the corpus luteum?

Answer 13

• develops from the ruptured dominant follicle after ovulation (triggered by LH)
• develops from the somatic cells in the follicle
• remains in ovary while oocyte travels through uterine tubes
• corpus luteum produces progesterone and oestrogen; which trigger proliferative phase of uterine cycle
• if pregnancy does not occur, corpus luteum degenerates into a corpus albicans (mass of fibrous scar tissue)

Question 14

what are the 4 main hormones involved in the menstrual cycle?

Answer 14

FSH:

• released by anterior pituitary gland in response to GnRH from hypothalamus
• follicle stimulating hormone
• triggers follicular phase of ovarian cycle (selection and maturation of dominant follicle in ovary)

LH:

• luteinzing hormone
• released from anterior pituitary in response to GnRH from hypothalamus
• triggers oestrogen production from granulosa cells in ovary
• triggers ovulation and converts ruptured follicle into corpus luteum

Oestrogen:

• released in response to LH (which is released by anterior pituitary in response to GnRH from hypothalmus)
• produced by granulosa cells in dominant follicle of ovary
• triggers regrowth of functional endometrium in proliferative stage of uterine cycle

Progesterone:

• released by corpus luteum
• triggers proliferative phase of uterine cycle