Exam 4 (Lecture 55) - Follicular Phase

Question 1

Name the two subphases of the follicular phase and the concentration trends of the major hormones (P4, E2, LH and FSH) during these two subphases.

Answer 1

1) Proestrus:
- P4 plummets
- E2, LH, and FSH all start to rise

Question 2

Which of the four major hormones is most responsible for estrus, especially the physical manifestations of estrus?

Answer 2

Estrogen

Question 3

Name the sources (cells or structures) of the four major hormones.

Answer 3

E2: Follicle

P4: CL

LH: Anterior pituitary

FSH: Anterior pituitary

Question 4

Explain follicular waves, follicular cohorts, super ovulation, and cystic ovaries.

Answer 4

1) Follicular Waves:
- The part of follicular development whereby the maturation process occurs two to three times per cycle

2) Follicular Cohorts:
- A group of primordial follicles that are physically grouped (recruited) and mature into small follicles
- A portion of these follicles undergo atresia while another cohort mature into medium follicles

3) Superovulation:
- The process in which the ovary is pharmacologically “nudged” to ovulate more than one ovum
- Chemical analogs of LH and FSH are given to override the inhibitory effects of inhibin
- Used in embryo transfer to maximize the number of ova that can be fertilized

4) Cystic Ovaries:
- Pathologic situation in which the follicle fails to ovulate
- Animal goes into anestrus and isn’t cycling
- Often related to metabolic deficits in the lactating dairy cow
- Treatment involves a GnRH analog +/- manual rupture via palpation

Question 5

Discuss the changes in the ovary that accompany the follicular phase.

Answer 5

1) The ovaries are loaded with primordial follicles (tiny follicles)
2) A cohort of follicles are the physically recruited and mature into small follicles
3) A portion of these undergo atresia while another cohort mature into medium follicles
4) A very small number of medium follicles mature into large follicles, the rest undergo atresia
5) One of the large follicles exerts a dominant effect on all other large follicles
6) The dominant follicle becomes the follicle that is ovulated from the ovary

*As the follicle develops, a fluid-filled sac enlarges and encompasses the ovum.
- The sac is termed the antrum

• Once the antrum surrounds the ovum and occupies most of the follicle, the ovum is discharged from the ovary.

Question 6

Discuss the relationship between LH, FSH, theca cells, granulosa cells, and the enzymatic synthesis of estrogen.

Answer 6

1) Granulosa cells are inside the follicle near the ovum

2) Theca cells are outside the follicle (on the periphery)

• These two cell types work in concert to stimulate production and release of estrogens from the granulosa cells
• GnRH is released from the hypothalamus where it stimulates the release of FSH and LH from the anterior pituitary
• LH activates receptors on theca cells and granulosa cells while FSH activates receptors only on granulosa cells
• LH stimulates the synthesis of testosterone in the theca cells
• Testosterone diffuses toward the granulosa cell where it is converted to estrogen by an enzyme aromatase that is activated by FSH
• Estrogen then diffuses into the blood

Question 7

Discuss the basis for the differing amounts of LH and FSH present during the follicular phase, even though the release of both is equally stimulated by GnRH.

Answer 7

Inhibin prevents the further release of FSH and allows LH to be released (LH surge):

  - The dominant follicle releases large amounts of E2 plus inhibin (thus GnRH is released in large quantities)

  - This causes the LH to be released in large quantities (LH surge) while inhibin continues to hamper FSH

Question 8

Discuss, in general terms, the seven feedback mechanisms occurring during the follicular phase (slide 20).

Answer 8

1) P4 prevents GnRH release at the hypothalamus

2) GnRh promotes LH and FSH release at the anterior pituitary

3) LH and FSH promote E2 synthesis in the follicle

4) E2 promotes GnRH release from the hypothalamus

5) E2 promotes its own synthesis at the follicle (granulosa cell)

6) Inhibin prevents FSH release from the AP (makes sure it stays at a modest level)

7) E2 promotes the LH surge from the AP at ovulation