BIO 304 · Human Anatomy & Physiology
Male Reproductive System
Reproductive System · Module 16
A reference for the Male Reproductive video. The testes both produce sperm and produce testosterone. Sperm travel a long path through ducts and accessory glands before they are ready to leave the body.
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- Identify the male reproductive organs and trace the path of sperm from production to ejaculation.
- Describe spermatogenesis and the role of Sertoli and Leydig cells.
- Outline the hormonal control of testicular function via the HPG axis.
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Anatomy & Sperm Path
Testes & descent
- Testespaired gonads outside body in scrotum (~2°C cooler for spermatogenesis)
- Scrotumpouch; dartos & cremaster muscles adjust temperature
- Inguinal canalfetal descent path; vulnerable to hernia
- Tunica albugineafibrous capsule of testis; divides into lobules
- Seminiferous tubuleswhere sperm are made; coiled tubes inside lobules
Sperm path (the route)
- Seminiferous tubulesite of spermatogenesis
- Rete testismerging tubules
- Efferent ductulesinto epididymis
- Epididymisstorage & maturation (sperm gain motility here)
- Vas (ductus) deferenslong muscular tube up through inguinal canal
- Ejaculatory ductwhere vas meets seminal vesicle duct
- Urethraprostatic → membranous → spongy; final passage out
Accessory glands
- Seminal vesiclesadd fructose, prostaglandins, alkaline fluid; ~60% of semen volume
- Prostatemilky alkaline secretion with PSA, citrate; ~30% of semen
- Bulbourethral (Cowper) glandspre-ejaculate; neutralizes urethra; lubrication
Penis & function
- Corpora cavernosa (2)erectile tissue; fill with blood for erection
- Corpus spongiosumsurrounds urethra; remains less rigid
- Glanstip; head of penis
- Erectionparasympathetic; NO triggers vasodilation
- Ejaculationsympathetic; smooth muscle contraction of ducts and glands
Spermatogenesis & Hormones
Cells of the testis
- Spermatogoniagerm-cell stem cells at outer wall of tubule
- Primary spermatocytesmeiosis I begins
- Secondary spermatocytesafter meiosis I
- Spermatidsafter meiosis II; haploid
- Spermatozoaafter spermiogenesis; mature shape
- Sertoli cells"nurse cells"; blood-testis barrier; support sperm development; make inhibin
- Leydig (interstitial) cellsoutside tubules; make testosterone in response to LH
Sperm structure
- Headnucleus + acrosome (enzymes for penetration)
- Midpiecemitochondria spiral; ATP for motility
- Tailflagellum; whip-like motion
- Production rate~200 million per day; ~64 days to mature each
HPG axis (male)
- Hypothalamusreleases GnRH (pulsatile)
- Anterior pituitaryGnRH triggers LH and FSH
- LHacts on Leydig cells; drives testosterone
- FSHacts on Sertoli cells; supports spermatogenesis + inhibin
- Testosteronenegative feedback on GnRH and LH; also pubertal changes
- Inhibinfeedback inhibitor of FSH; from Sertoli
Testosterone effects
- Primary sex characteristicsgenital development
- Secondary characteristicsfacial/body hair, deep voice, muscle mass, bone density
- Libido and spermatogenesisdriven by sustained testosterone
- Anabolic effectsmuscle and bone; basis for sports doping
Semen
- Volume2-5 mL per ejaculate
- Sperm count40-300 million/mL normal
- Componentssperm + accessory gland secretions
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