Reproductive Endocrinology

Question 1

How many carbons in different steroid derivatives?

Answer 1

Cholesterol - 27
Glucocorticoids, Mineralocorticoids, Progestins - 21
Testosterone - 19
Estrogen - 18

Question 2

20,22 Desmolase

Answer 2

Catalyzes cleavage of the cholesterol side chain, which is the rate limiting step of steroid synthesis; results in production of pregnenolone

Located in the mitochondrial membrane

Question 3

Where is testosterone produced?

Answer 3

In men - 95% in testes, 5% in adrenal gland

In women - 50% in ovaries, 50% in adrenal gland

Question 4

Dihydrotestosterone (DHT)

Answer 4

Produced from testosterone by 5-alpha reductase in the prostate and skin

Cannot be converted to estrogens

Question 5

Androstenedione

Answer 5

Precursor for ovarian estradiol production by granulosa cells, and for extraglandular estrogen formation in the liver and adipose tissue

Question 6

Estrone (E1)

Answer 6

Produced via peripheral conversion of androstenedione by aromatase in adipose

Question 7

Estradiol (E2)

Answer 7

Most potent / major circulating form of estrogen; produced by granulosa cells of the ovary in females and by Sertoli cells of the testes in males

Question 8

Estriol (E3)

Answer 8

Least potent; produced by the placenta during pregnancy

Question 9

Which hormonal mediators share the same alpha subunit?

Answer 9

FSH
LH
hCg
TSH

Question 10

Leydig Cells

Answer 10

Produce 95% of male testosterone in response to LH from pituitary; LH stimulates rate-limiting conversion of cholesterol to pregnenolone by up-regulating desmolase activity

Testosterone acts on Sertoli cells to support spermatogenesis and exerts negative feedback on the hypothalamus and pituitary

Unable to produce estrogens (absence of aromatase)

Question 11

Sertoli cells

Answer 11

Organized into seminiferous tubules in which maturation of spermatogonia occurs

Activation by FSH causes increased production of androgen binding protein, enhanced conversion of testosterone from Leydig cells into estradiol, and production of Inhibin

Question 12

Theca Cells

Answer 12

Activated by LH to convert cholesterol to pregnenolone; pregnenolone is converted to progesterone and then to androstenedione

Lack aromatase; androstenedione must diffuse from theca cell into granulosa cell for conversion to estrogen

Question 13

Granulosa cells

Answer 13

Exist in direct contact with oogonia; gametes + surrounding granulosa cell = ‘primordial follicles’

Granulosa cells lack the enzyme needed to convert progesterone into androgens; progesterone from granulosa cells must diffuse into theca cells for conversion to androstenedione

Androstenedione from theca cells diffuses to granulosa cells for conversion to Testosterone and Estrone (E1)