Menstrual Cycle

Question 1

Describe a normal menstrual cycle: Length, duration etc.

Answer 1

Normal length: 24-35 days

Bleeding

Question 2

Describe the pattern of GnRH secretion. How is it different in follicular phase vs. luteal phase?

Answer 2

GnRH has a short half life and is secreted in a pulsatile fashion.

Follicular phase: secreted more frequently (60-90min) with lower amplitude
Luteal phase: secreted less often (3-5hr) with higher amplitude– favors FSH secretion

Question 3

What are the main functions of FSH? (4)

Answer 3

1. Stimulate granulosa cell proliferation (needed for growth past antral stage)
2. Stimulates aromatase activity in granulosa cells: increases estrogen
3. Up-regulates LH/FSH receptors
4. Recruits follicles for next cycle

Question 4

Describe the regulation of gonadotropins during the follicular phase: How is FSH regulated? What is responsible for the LH surge?

Answer 4

Estrogen at lower levels provides negative feedback on pituitary/hypothalamus: Decreased FSH towards end of follicular stage

Above threshold level, estrogen provides positive feedback: increased GnRH pulses leads to increased LH

Question 5

What is responsible for recruitment of follicles to begin menstrual cycle?

Answer 5

Rise in FSH at end of one cycle and beginning of next

Question 6

What are the results of the LH surge? (3)

Answer 6

1. Release of oocyte from follicle (ovulation) 36hr after beginning of surge
2. Luteinization of granulosa cell: Increased progesterone production
3. Extrusion of 1st polar body and resumption of meiosis

Question 7

What are effects of estrogen and progesterone during luteal phase? (1)

Answer 7

Suppress gonadotropin release

Question 8

What is effect of estrogen on uterus? (3) When is its effect most prominent?

Answer 8

Estrogen acts on uterus during follicular phase:

1. Promotes reconstruction/growth
2. Increases glands
3. Mitoses become more prominent

Question 9

What is effect of progesterone on uterus? (3) When are its effects most prominent?

Answer 9

Progesterone acts on uterus during luteal phase (made by luteinized cells)

1. Limits growth, mitosis, DNA synthesis
2. Increases tortuosity of glands and intensifies coiling of spiral vessels
3. Secretion of glycoproteins and peptides into cavity

Question 10

Luteal phase: What are events if fertilization does not occur?

Consider corpus luteum, progesterone, estrogen and FSH.

Answer 10

Degeneration of corpus luteum leads to drop in estrogen and progesterone
Withdrawal of progesterone causes endometrial sloughing
Withdrawal of estrogen removes negative feedback on FSH

Question 11

Luteal phase: What are events if fertilization does occur?

Consider corpus luteum, estrogen and progesterone.

Answer 11

Embryo makes hCG, which maintains corpus luteum. Corpus luteum continues to make progesterone and estrogen so no menstruation. No period

Question 12

Describe the structures of activins and inhibins

Answer 12

Activin: 2ß subunits
Inhibin: A and ß subunit (can be A or B)

Question 13

Which cell type produces inhibin? What are the functions of inhibit? (3)

Answer 13

Inhibin is produced by granulosa cells.

Inhbiin blocks FSH synthesis/secretion
Increases LH receptors on theca cells
Competes for activin receptors and inactivates activin

Question 14

Where is activin produced? What is its function?

Answer 14

Activin is produced in gonads.
Function: augment FSH actions.
Enhances GnRH activity by increasing GnRH receptors, and augmenting FSH secretion.

In follicle, activin promotes granulosa proliferation, increases FSH receptors and increases stimulation of aromatase