Follicular Phase Of The Menstrual Cycle

Question 1

The follicular phase is the term given to the

Answer 1

first approximately 14 days of the menstrual cycle.

Question 2

It is composed of both an

Answer 2

endocrine-independent and an endocrine-dependent development of ovarian follicles.

Question 3

Every day a group of approximately ______________oocytes begin to grow in the ovary (Eldar-Geva et al. 2000).

Answer 3

50

Question 4

Mechanisms involved in determining the selection of oocytes and oocyte stimulation within the primary follicles have been the focus of many studies in recent years and a picture, albeit incomplete, of factors involved and how they function is gradually emerging. Evidence from animal models has brought to light complex intra-ovarian control mechanisms that involve

Answer 4

members of the TGFB super family, in particular BMP15 and GDF9 subfamilies, kit ligand, leukemia inhibitory factor (LIF), and AMH in the recruitment process (Knight and Glister, 2006).

Question 5

Deletion or disruption of the BMP15 gene results in

Answer 5

impaired early folliculogenesis making it a good candidate in the search for signals that trigger the initial growth of primordial follicles.

Question 6

However, primordial follicle activation is likely dependent upon

Answer 6

the activities of several inhibitory and stimulatory molecules some of which are only now being identified.

Question 7

The selection of the follicles for activation appears to be

Answer 7

random and is not hormonally stimulated.

Question 8

These waves of follicles grow for over 10 months after which

Answer 8

most undergo atresia.

Question 9

A small group of 5-10 developing follicles per ovary are rescued from atresia once a month by the

Answer 9

increasing systemic concentrations of FSH that are present during the early follicular phase (cyclic recruitment).

Question 10

The continued development of this small group of antral follicles is therefore purely due to good fortune; that is, their development happens to

Answer 10

coincide with an appropriate hormonal milieu.

Question 11

An antral follicle count (AFC) using ultrasound early in the menstrual cycle can be used as a means of

Answer 11

assessing ovarian reserve and an indication of the likelihood of obtaining sufficient growing follicles in an IVF treatment cycle after ovarian stimulation.

Question 12

Estrogen and progesterone concentrations are low during the early stages of the follicular phase leading to a

Answer 12

subtle but continuous increase in FSH and LH (removal of steroid negative feedback).

Question 13

Increasing systemic concentrations of FSH stimulate

Answer 13

antrum formation in the rescued follicles and also stimulate GC division (hyperplasia) resulting in an exponential growth in GC numbers.

Question 14

FSH and LH also stimulate the steroid synthetic pathways of

Answer 14

the GC to produce estrogen.

Question 15

Since GC numbers increase exponentially the

Answer 15

estrogen concentration also increases in an exponential fashion until peak systemic concentrations (-200-300 pg/mL) occur just prior to ovulation.

Question 16

The rising concentrations of estradiol have three important influences on the early menstrual cycle:

Answer 16

1. Endometrial cell preparation
2. Dominant follicle selection
3. Induction of the LH surge

Question 17

Estradiol simulates the proliferation of endometrial cells and prepares the intracellular mechanisms of the endometrial cells for

Answer 17

the subsequent actions of progesterone later in the menstrual cycle.

Question 18

Of the 5 to 10 follicles per ovary that were initially recruited by FSH for development, only

Answer 18

one or two will develop into a preovulatory state.

Question 19

The elevated levels of estrogen prior to ovulation cause a

Answer 19

decrease in FSH levels in response to negative feedback.

Question 20

Ovarian inhibin may also participate in

Answer 20

suppressing FSH pituitary output and closing the FSH window.

Question 21

Decreased FSH levels may partially be responsible for

Answer 21

selection of the dominant preovulatory follicle by the production of a more androgenic microenvironment within follicles adjacent to the growing dominant follicle.

Question 22

Furthermore, the GC of the dominant growing follicle secrete a variety of peptides that

Answer 22

may inhibit development of the adjacent follicles via an autocrine/paracrine mechanism.

Question 23

AMH produced by the GC is also believed to play a role in

Answer 23

dominant follicle selection.

Question 24

The mechanism(s) of dominate follicle selection have been well studied and while a definitive mechanism(s) is/are not entirely clear a favored current theory proposes follicle dominance arises by

Answer 24

selective follicular sensitization leading to enhanced FSH responsiveness and ability to continue development in an environment with low FSH levels.

Question 25

High estradiol concentrations towards the end of the follicular phase induce

Answer 25

the LH surge that stimulates the ovulatory response and the resumption of meiosis by the oocyte.

Question 26

As part of the ovulatory response, the LH surge luteinizes

Answer 26

the GC to form the corpus luteum and converts the steroidogenic pathway from a predominately estrogen-producing system to a predominately progesterone-producing system.