General Overview of Reproductive Axis I & II

Question 1

Characteristics of reproductive axis

Answer 1

• Age-related component (pre-oubertal vs post etc)
• Boys and girls are different
• 2 pituitary hormones(FSH & LH)
• 3 gonadal hormones that feedback
• Gonads are not the only source in the body for the 3 hormones

Question 2

Structure of FSH, LH, TSH, bHcG

Answer 2

Same alpha unit, different Beta subunit

Question 3

There are three major categories of sex steroids:

Answer 3

progestins, androgens, and estrogens

Question 4

The major classes of steroid hormones are

Answer 4

glucocortocoids, mineralocorticoids, and sex steroids

Question 5

Principle sources of sex steroids include:

Answer 5

the gonads, the adrenal cortex, and the placenta.

Question 6

what Peripheral tissues play key roles in the conversion and metabolism of sex steroids?

Answer 6

the skin, liver and adipose tissues

Question 7

Number of carbons in steroid hormones:

Answer 7

• glucocortocoids such as cortisol (C-21),
• mineralocorticoids such as aldosterone (C-21),
• sex steroids which include
• progestins (C-21),
• androgens (C-19), and
• estrogens (C-18).

Question 8

of carbons in cholesterol?

Answer 8

27, progressively reduced to form steroid hormones

Question 9

Summarize conversion of cholesterol to steroid hormone

Answer 9

By a process which includes a reduction in the size of the hydrocarbon side-chain and hydroxylation of the 4-ring steroid nucleus, resulting in a structurethat is a 21-carbon compound known as pregnenolone. Pregnenolone is then converted into all other sex steroids
-Rate limiting step is catalyzed by side chain cleaving enzyme, 20, 22 desmolase, in mitochondrial membrane.

Question 10

Progestins

Answer 10

• 21 carbons
• Include: pregnenolone, 17-alpha-hydroxy-pregnenolone, progesterone, and 17-alpha- hydroxy-progesterone (17-OH-P)
• precursors for the production of aldosterone and cortisol by the adrenal gland

Question 11

Key functions of progesterone

Answer 11

growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation

Question 12

Androgens

Answer 12

-19 carbonsvia pregnenolone
-Include e testosterone, dehydroepiandrosterone (DHEA), dehydroepiandrosterone-sulfate (DHEA-S), dihydrotestosterone (DHT), and androstenedione.
-

Question 13

Major source of testosterone

Answer 13

95% gonads, rest is adrenal

Question 14

5-alpha-reductase

Answer 14

the enzyme which converts testosterone to dihydrotestosterone (DHT) in target cells such as those located in the prostate and skin (30-50 times more active that testosterone)

Question 15

Effect of testosterone

Answer 15

• androgenic: growth and development of the internal and external genitalia, the development and maintenance of secondary sex characteristics, spermatogenesis, and sexual fantasies and libido. and sebum
• anabolic: growth-promoting effects on somatic tissues such as bone and muscle

Question 16

Feedback regulation of hypothalamic – pituitary – testicular axis,

Answer 16

testosterone acts as a key feedback inhibitor at the levels of hypothalamus and pituitary

Question 17

Estrogens

Answer 17

• 18-carbon sex steroids
• Androgens are converted into the estrogens
• The estrogens synthesized in the human body include estrone (E1), estradiol (E2) and estriol (E3) (hydroxyl groups.
• estradiol is the most potent and estriol (from placenta only) is the least.
• Estrogens affect uterus, the ovaries, and the breasts.

Question 18

Aromatase

Answer 18

Aromatase is present in the gonads and in various peripheral tissues including adipose tissue, liver, ands the CNS. Converts androgens to estrogens.

Question 19

-Key functions of estradiol include

Answer 19

the growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation.

Question 20

Feedback regulation of the hypothalamic – pituitary – ovarian axis

Answer 20

, estradiol acts as a key feedback inhibitor at the levels of hypothalamus and pituitary.

Question 21

Plasma proteins that bind sex hormones

Answer 21

albumin, sex hormone binding globulin (SHBG), and corticosteroid binding globulin (CBG).

Question 22

2 key concepts of hypo-pit-gonad axis

Answer 22

• Feedback regulation

- 2 cell synthesis in gonads

Question 23

Reason for GnRH secretion pulsatility is

Answer 23

key to the physiologic stimulation of the anterior pituitary as constant administration of GnRH actually suppresses the pituitary response

Question 24

primary hormone regulators of gonadal function in both sexes.

Answer 24

FSH and LH from ant pit

Question 25

LH and FSH stimulate the production of

Answer 25

sex steroids and inhibin

Question 26

The sex steroids exert negative feedback control on the reproductive axis at both the

Answer 26

hypothalamic and pituitary levels.

Question 27

Inhibin exerts negative feedback control on the reproductive axis exclusively at the level of

Answer 27

the pituitary.

Question 28

When is +ve feedback exerted?

Answer 28

ovarian estradiol At midcycle in ovulatory women,

, leading to a surge in FSH and LH.

Question 29

gonadal sex steroid production and gametogenesis in testes

Answer 29

Leydig and Sertoli cells.

Question 30

gonadal sex steroid production and gametogenesis in ovaries

Answer 30

theca and the granulosa cells

Question 31

male Leydig and female theca cells common features. These include the

Answer 31

-Interstitial cells
presence of LH receptors,
-ability to make androgens,
-inability to make estrogens due to the absence of aromatase.

Question 32

male Sertoli and female granulosa cells common features

Answer 32

immediately adjacent to the developing gametes and

• presence of FSH receptors,
• ability to make inhibin,
• ability to convert androgens into estrogens due to the presence of aromatase.

Question 33

The Leydig cells

Answer 33

• occupy the interstitial layer surrounding the seminiferous tubules. ,
• Leydig cells produce ~95% of the testosterone (from cholesterol) in males In response to LH.
• resulting testosterone acts on the Sertoli cells to support spermatogenesis.

Question 34

LH stimulates the rate-limiting conversion of cholesterol into pregnenolone in two ways:

Answer 34

by increasing the amount of desmolase and by enhancing the affinity of desmolase for cholesterol.

Question 35

The Sertoli cells

Answer 35

• support or nurse cells of the developing spermatozoa.
• organized into a tubular epithelium known as the seminiferous tubule (tight gap junctions between adjacent Sertoli cells).
• Maturing spermatogonia are located between adjacent Sertoli Cells.
• primary source of inhibin in males

Question 36

FSH binding to Sertoli cells effects

Answer 36

increased production of androgen binding protein, enhanced conversion of testosterone from the Leydig cells into estradiol, and the production of inhibin.

Question 37

theca cells

Answer 37

• are located in the ovarian stroma surrounding the follicles
• theca cells produce progesterone and androgens.
• lack aromatase and therefore the capacity to produce estrogens.
• Androstenedione from the theca cells must therefore diffuse into nearby granulosa cells for estrogen to be produced.

Question 38

The ovarian granulosa cells

Answer 38

• are in direct contact with the oogonia
• Granulosa cells lack the enzyme which converts progesterone into androgens.
• Progesterone from the granulosa cells must therefore diffuse to the theca cells where it is converted into androstenedione.