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Male Reproductive Physiology
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Male Reproductive Physiology

Hypothalamic-pituitary-gonadal axis
  • Regulates male reproduction hormones (like female reproductive hormones).
  • Testosterone and other key hormones influence sperm cell production (spermatogenesis) and development of male physical characteristics
GnRH
Stimulates the anterior pituitary gland to release into the bloodstream:
  • Luteinizing hormone (LH, aka, interstitial cell-stimulating hormone)
  • Follicle-stimulating hormone (FSH)
These hormones are called gonadotropins because they act on the gonads
LH
  • Binds interstitial cells and triggers release of testosterone.
Testosterone
  • Paracrine effects include stimulation of sustentacular cells, which promotes spermatogenesis within the seminiferous tubules.
  • Endocrine effects are such that testosterone also leaves the testes via the bloodstream and acts in the maintenance of primary and secondary sexual characteristics.
As examples, it increases: Penis, scrotum, and testes size. Musculoskeletal density and mass. Hair growth and sebaceous gland activity. And enlarges the larynx (aka, "voicebox"), which deepens the voice.
FSH
  • Stimulates sustentacular cells to trigger release of spermatogenic secretions; thus, in conjunction with testosterone, FSH directly promotes sperm cell formation.
  • Inducing sustenacular cell release of androgen-binding protein, a hormone that binds to testosterone (and other androgens) and keeps local concentrations high.
Negative Feedback Processes:
Testosterone
  • Inhibitory effects on hypothalamic secretion of GnRH and anterior pituitary release of LH; thus, testosterone inhibits its own production.
  • In response to high concentrations of FSH and testosterone, the sustenacular cells release another hormone, inhibin.
Inhibin
  • Inhibits release of FSH from the anterior lobe of the pituitary gland; in the absence of FSH, the sustentacular cells cannot support spermatogenesis.

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