Reproduction 2 Flashcards
What is the major hypothalamic hormone in the HPG axis?
GnRH/LHRH- absolutely required and must be released in a pulsatile fashion
What is the major pituitary hormone in the HPG axis?
LH and FSH
What does LH do?
stimulates steroidogenesis in the ovaries and testes
What does FSH do?
stimulates gametogenesis in the ovaries and testes
What are some regulators of GnRH?
Kisspeptin, gonadal steroid hormones
GnIH, prolactin, neurotransmitters (GABA), cortisol (stress), growth factors (TGFα/β), neuropeptides (opiods, melatonin)
Almost all inhibit GnRH
What does Kisspeptin do?
Required to increase release of GnRH at time of puberty.
Presumed signal for pubertal onset
Mutations in KISS1 receptor cause hypogonadotropic hypogonadism
What do inhibins and activins do in the pituitary?
Inhibins inhibit FSH specifically
Activins are expressed in the pituitary and the gonads, stimulate FSH-beta, LH-beta, and GnRH receptor synthesis in the pituitary
Where is inhibin B especially expressed?
gonads
How is LH activated?
via fast GnRH pulses
How is FSH activated?
via slow GnRH pulses
What cells have a high number of FSH receptors?
Sertoli cells: form the blood-testes barrier
What are the six things that FSH stimulates in the testes?
Stimulates spermatogenesis - Increases sperm motility
Stimulates growth of seminiferous tubules – primary determinant of testes size
Stimulates androgen binding protein (ABP) – maintains high local T
Stimulates aromatase
Stimulates inhibin
Stimulates growth factors
What does aromatase do?
Converts estosterone to estradiol
What cells have a high number of LH receptors?
Leydig cells
What effects does LH have on Leydig cells?
Stimulates steroidogenesis from cholesterol
Androgens = 19 carbon steroids
Stimulates StAR protein – rate limiting
Stimulates Leydig cell growth
Where are testosterone precursors made?
extragonadal tissues: brain, adrenal, skin, adipose tissue
What is the primary source of circulating T?
Testes
in what form is testosterone found in the blood?
bound to SHBG
What is testosterone converted to intracellulary
DHT or estrogens
What common receptor does T and DHT bind?
Androgen receptor (AR) - a nuclear steroid receptor
DHT has higher affinity
How much of the daily production of testosterone is excreted as free testosterone?
What is the remaining, non-excreted testosterone converted to?
17-ketosteroids & DHT –> conjugated to water soluble forms and excreted.
What does masculinization of the brain require?
T to E conversion
What is DHT responsible for?
male pattern baldness
during fetal development, what does testosterone stimulate?
epididymis, vas deferens, seminal vesicles
during pubertal development, what does testosterone stimulate?
penis, seminal vesicles, musculature, voice, skeleton, spermatogenesis
during fetal development, what does DHT stimulate?
penis, penile urethra, scrotum, prostate
during pubertal development, what does DHT stimulate?
scrotum, prostate, male pattern hair distribution, beard, sebaceous glands