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

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.

Male Reproductive Physiology

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