Reproductive Endocrinology Flashcards
what is the function of the testes?
production of spermatozoa and is also an endocrine organ
what are the two main parts of the testes?
- seminiferous tubules
- leydig cells/interstitial cells
what do the seminiferous tubules contain?
steroli cells
what are sertoli cells?
endocrine cells that produce inhibins and factors (eg androgen binding protein) that promote spermatogenesis
what are leydig cells?
major endocrine cells of testes
what do leydig cells produce?
sex steroid hormones (primarily testosterone, also DHT, estradiol, and others) and activins
what are the two important protein/enzyme in leydig cells?
- steroidogenic acute regulatory protein (STAR)
- cytochrome P450 enzyme
what does the STAR protein do?
regulates cholesterol transfer within the mitochondria
what is cytochrome P450?
large family of enzymes that catalyze oxifation; key for steroid hormone biosynthesis
what happens in the mitochondria with cytochrome P450?
side chain cleavage enzyme (P450SCC) converts cholesterol to pregnenolone
in leydig/interstitial cells there is no synthesis of…
glucocorticoids or mineralocorticoids (eg lack cytochrome P450 enzyme 21-a-hydroxylase)
in leydig/interstitial cells, pregnenolone is translocated to _____ for conversion ____.
smooth ER, testosteron
the conversion to testosterone in leydig cells happens via 2 routes:
- progesterone or dehydroepiandrosterone/DHEA is an intermediate
what are the three main steroid hormones in male reproductive biology?
- testosterone
- dihydrotestosterone
- estradiol
testosterone
predominant androgen (=’hormone that primarily influenxes the growth and development of the male reproductive system’) produced by leydig/interstitial cells
DHT (dihydrotestosterone)
potent androgen - the more active androgen form
how is DHT produced in the body?
in many androgen target tissues, testosterone is converted by 5α-reductase into the more potent androgen DHT
how do DHT and testosterone interact w androgen receptors?
bind to the same androgen receptor but DHT has higher affinity
estradiol
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
testosterone and DHT functions include:
- 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
function of estradiol in males
- critical role in male sexual function
- role in promoting pubertal growth spurt
what are the primary binding proteins for approx 60% of T in circulation
sex hormone binding globulin (SHBG), a glycoprotein synthesized in the liver, binds w high affinity to t, DHT and estrogens
what is the androgen signal transduction pathway
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)
androgens may also exhibit..
rapid effects through nonclassical signaling
