Reproductive Endocrinology

Question 1

what is the function of the testes?

Answer 1

production of spermatozoa and is also an endocrine organ

Question 2

what are the two main parts of the testes?

Answer 2

• seminiferous tubules
• leydig cells/interstitial cells

Question 3

what do the seminiferous tubules contain?

Answer 3

steroli cells

Question 4

what are sertoli cells?

Answer 4

endocrine cells that produce inhibins and factors (eg androgen binding protein) that promote spermatogenesis

Question 5

what are leydig cells?

Answer 5

major endocrine cells of testes

Question 6

what do leydig cells produce?

Answer 6

sex steroid hormones (primarily testosterone, also DHT, estradiol, and others) and activins

Question 7

what are the two important protein/enzyme in leydig cells?

Answer 7

• steroidogenic acute regulatory protein (STAR)
• cytochrome P450 enzyme

Question 8

what does the STAR protein do?

Answer 8

regulates cholesterol transfer within the mitochondria

Question 9

what is cytochrome P450?

Answer 9

large family of enzymes that catalyze oxifation; key for steroid hormone biosynthesis

Question 10

what happens in the mitochondria with cytochrome P450?

Answer 10

side chain cleavage enzyme (P450SCC) converts cholesterol to pregnenolone

Question 11

in leydig/interstitial cells there is no synthesis of…

Answer 11

glucocorticoids or mineralocorticoids (eg lack cytochrome P450 enzyme 21-a-hydroxylase)

Question 12

in leydig/interstitial cells, pregnenolone is translocated to _____ for conversion ____.

Answer 12

smooth ER, testosteron

Question 13

the conversion to testosterone in leydig cells happens via 2 routes:

Answer 13

• progesterone or dehydroepiandrosterone/DHEA is an intermediate

Question 14

what are the three main steroid hormones in male reproductive biology?

Answer 14

• testosterone
• dihydrotestosterone
• estradiol

Question 15

testosterone

Answer 15

predominant androgen (=’hormone that primarily influenxes the growth and development of the male reproductive system’) produced by leydig/interstitial cells

Question 16

DHT (dihydrotestosterone)

Answer 16

potent androgen - the more active androgen form

Question 17

how is DHT produced in the body?

Answer 17

in many androgen target tissues, testosterone is converted by 5α-reductase into the more potent androgen DHT

Question 18

how do DHT and testosterone interact w androgen receptors?

Answer 18

bind to the same androgen receptor but DHT has higher affinity

Question 19

estradiol

Answer 19

predominant form of estrogen ( = “hormone that primarily influences the
growth and development of the female reproductive system”);
estradiol also plays a critical role in male sexual function

Question 20

testosterone and DHT functions include:

Answer 20

• differentation of internal and external male reproductive system during fetal development
• growth of male reproductive system organs during puberty
• stimulation of growth or skeletal muscles
• promotes libido, spermatogenesis in sertoli cells

Question 21

function of estradiol in males

Answer 21

• critical role in male sexual function
• role in promoting pubertal growth spurt

Question 22

what are the primary binding proteins for approx 60% of T in circulation

Answer 22

sex hormone binding globulin (SHBG), a glycoprotein synthesized in the liver, binds w high affinity to t, DHT and estrogens

Question 23

what is the androgen signal transduction pathway

Answer 23

Free T or free DHT enters the cell;
In many target ,ssues, testosterone is enzyma,cally
converted by 5α-reductase to the more potent DHT
* DHT & testosterone bind to the same intracellular
androgen receptor (DHT has higher binding affinity)
* Androgen receptor: cytosolic/nuclear receptor
(member of the steroid-thyroid hormone nuclear
receptor superfamily)
* When testosterone or DHT binds to cytosolic
androgen receptor, it dissociates from heat shock &
chaperone proteins, forms a homodimer with another
androgen-receptor complex and is translocated into
the nucleus
* Binds to androgen response elements in DNA and
interacts with protein coactivators to initiate
transcriptional activity (effects in hours to days)

Question 24

androgens may also exhibit..

Answer 24

rapid effects through nonclassical signaling