Overview
This lecture introduces the male reproductive system, focusing on gamete production, anatomy, hormonal control, and the pathway of sperm through the male reproductive tract.
Gametes and Gonads
- Gametes are reproductive (sex) cells: sperm (male), oocyte (female).
- Gonads produce gametes and sex hormones: testes (male), ovaries (female).
- Males produce sperm daily after puberty; females are born with all their oocytes.
Male Reproductive System Anatomy
- Testes produce sperm, stored in the epididymis.
- Duct system transports sperm: epididymis → vas deferens → ejaculatory duct → urethra.
- Accessory glands: seminal vesicles (produce most semen, fructose-rich and alkaline), prostate gland (prostatic fluid, PSA), bulbourethral gland (lubrication).
- External genitalia: penis (copulation organ) and scrotum (houses testes).
Sperm Production and Maturation
- Spermatogenesis is sperm production in seminiferous tubules.
- Spermatogonia (stem cells) divide under stimulation by testosterone from interstitial endocrine cells.
- Nurse (Sertoli) cells create blood-testis barrier, nourish, and protect developing sperm.
- Sperm structure: head (nucleus, acrosome), neck (mitochondria), tail (flagellum for movement).
- Sperm mature in epididymis but require capacitation (in female tract) to fertilize an oocyte.
Semen Composition and Ejaculation
- Semen: mixture from epididymis (5%), seminal glands (60%), prostate (20-30%), bulbourethral glands (5%).
- Ejaculation involves rhythmic muscle contractions (bulbospongiosus and ischiocavernosus).
- Average ejaculate: 2–5 mL, with 50–150 million sperm/mL.
Temperature Regulation and Testicular Descent
- Scrotum keeps testes ~4°F cooler than body for sperm production.
- Dartos muscle wrinkles scrotal skin (reduces heat loss).
- Cremaster muscle moves scrotum closer/further based on temperature.
- Testes descend into scrotum before birth via gubernaculum testis.
Sperm Pathway (Mnemonic: 7UP)
- Seminiferous tubules → Epididymis → Vas deferens → Ejaculatory duct → Urethra → Penis.
Penile Structure and Erection
- Penis has three erectile tissues: two corpora cavernosa, one corpus spongiosum (surrounds urethra).
- Erection: blood fills erectile tissues (parasympathetic control).
- Ejaculation: smooth muscle contractions (sympathetic control).
Key Terms & Definitions
- Gametes — reproductive sex cells (sperm, oocytes)
- Gonads — organs producing gametes and hormones (testes, ovaries)
- Spermatogenesis — process of sperm production
- Epididymis — duct where sperm mature and are stored
- Seminal vesicles — glands producing fructose-rich, alkaline seminal fluid
- Prostate gland — produces prostatic fluid, contributes PSA
- Bulbourethral gland — secretes lubricating mucus
- Sertoli (nurse) cells — support/nourish developing sperm and form blood-testis barrier
- Capacitation — final maturation of sperm in female tract
- Tunica albuginea — dense tissue surrounding testis
- PSA — prostate-specific antigen, marker for prostate health
Action Items / Next Steps
- Review the 7UP mnemonic for sperm pathway.
- Prepare questions for next lecture on the female reproductive system.