07 - Actions of the gonadotropins

Question 1

(Actions of the Gonadotropins)

(FSH)

1-5 what five things?

Answer 1

1. granulosa cell differentiation (granulosa cells are a major component of ovarian follicles)
2. positively influences ovarian steroidogenesis by increasing levels of rate-limiting enzymes - especially aromatase (therefore increases estrogen production)
3. stimulates inhibin production (so directly involved in own inhibition)
4. acts with estrogen to increase FSH receptors
5. stimulates formaiton of receptors for LH and prolactin

Question 2

(Actions of the Gonadotropins)

(LH)

1-3. what three?

4-6. The LH surge also does what three things?

Answer 2

1. main controller for follicular steroidogenesis
2. maintains steroidogenic enzymes but also acts to increase substrate availability for steroidgenesis
3. adequate pulsatile secretion of LH is necessary to drive conversion of cholesterol (the steroidgenesis sustrate) to androgens (which can then be converted to estrogen)
4. sets in motion the ovulation cascade
5. induces granulosa cell luteinization
6. causes resumption of oocyte meiosis

Question 3

(Ovary)

First we will look at the mature follicle and its mechanism of steroidogenesis and include the mature corpus luteum that results from ovulation. This will enable us to complete our picture of the hypothalamo-pituitary-ovarian axis

Question 4

(Follicles)

1. The Graafian (mature) follicle consists of what?
2. the oocyte is contained in what?

Answer 4

1. an antrum wihich is the fluid filled area in the middle

surrounding this is a layer of granulosa cells

outside this is a basement membrane (membrane propria)

outside this again are the theca interna cells

2. in a ball of granulosa cells, the cumulus oophorus

this ball floats in a the follicular fluid of the antrum tethered by a stalk of granulosa cells to the granulosa layer of the follicle wall

Question 5

(Follicular Steroidogenesis)

1. The granulosa cells are the site of estrogen synthesis but they need the help of the what to complete the task?
2. While competent to produce everything down the steroidogenic cascade as far as progesterone, granulosa cells cannot do what?
3. On the other hand, theca cells can’t do what?
4. To get around this the follicles use what system in order to synthesize estrogens?

Answer 5

1. theca cells
2. convert progesterone to androgens
3. aromatize androgens to estrogens
4. two-cell two-gonadotropin model

Question 6

(Follicular Steroidogenesis)

(two-cell two-gonadotropin model)

1. LH stimulates synthesis of what?
2. The androgens (mainly androstenedione) then do what?
3. What happens in the granulosa to these androgens?

Answer 6

1. androgens in the theca interna
2. diffuse across basement membrane into the granulosa cells
3. they are aromatized to form estradiol under the influence of FSH

(progesterone produced by the granulosa may also move across the basement membrane into the theca cells to provide more substrate for androgen biosynthesis)

Question 7

(Inhibin)

1. Like FSH and LH, inhibin is a glycoprotein hormone composed of what?
2. It is produced in granulosa cells of the follicle under influence of what?
3. It specifically acts where to do what?

Answer 7

1. 2 dissimilar subunits alpha and beta
2. FSH and estrogen
3. the pituitary gland to decrease FSH secreiton

Question 8

(Corpus Luteum)

1. The LH surge induces luteinization of the granulosa cells of the follicle, so in most species they start to secrete some progesterone when?
2. After ovulation the granulosa and theca cells further differentiate to form what?
3. Progesterone secretion from this structure usually consists of a baseline intrinsic level upon which is superimposed an LH repsonsive component.

(look at graph… on 64)

Answer 8

1. prior to ovulation
2. the mature corpus luteum

Question 9

Answer 9