Male Reproductive System Notes

Fundamental Sex Distinctions

  • Male gamete: sperm (motile).
  • Female gamete: egg (provides nutrients).
  • Male produces sperm; has Y chromosome.
  • Female produces eggs; lacks Y chromosome.
  • In mammals, females provide internal environment and prenatal nutrition.

Reproductive System Functions

  • Male: produces sperm, introduces them into female body (penis).
  • Female: produces eggs, receives sperm, provides for gamete union, harbors fetus, nourishes offspring (vagina).

Reproductive System Organs

  • Primary sex organs (gonads): produce gametes (testes in male, ovaries in female).
  • Secondary sex organs: other organs necessary for reproduction.
    • Male: ducts, glands, penis.
    • Female: uterine tubes, uterus, vagina.
  • External Genitalia: located in the perineum.
  • Internal Genitalia: located in the pelvic cavity.

Male Reproductive System

  • Organs: testes, scrotum, penis, epididymis, urethra, ductus deferens, prostate gland, seminal gland.
  • Function: produce sperm and hormones.

Scrotum

  • Pouch containing testes; maintains lower temperature for sperm production (35°C).

Testes

  • Produce sperm and sex hormones.
  • Tunica albuginea: white fibrous capsule.
  • Seminiferous tubules: sperm production.
  • Interstitial endocrine cells: produce testosterone.

Spermatic Ducts

  • Efferent ductules: transport sperm from rete testes to epididymis.
  • Epididymis: sperm maturation and storage.
  • Ductus deferens: tube from epididymis to seminal vesicle.
  • Ejaculatory duct: formed by ductus deferens and seminal vesicle; empties into urethra.
  • Urethra: prostatic, membranous, and spongy regions.

Accessory Glands

  • Seminal vesicles: contribute 60% of semen.
  • Prostate: contributes 30% of semen; contains prostate-specific antigen (PSA).
  • Bulbourethral glands: produce lubricating fluid that neutralizes acidity of residual urine in urethra.

Penis

  • Deposits semen in vagina.
  • Contains corpus spongiosum (encloses urethra) and corpora cavernosa (erectile tissues).

Spermatogenesis

  • Sperm production in seminiferous tubules involving meiosis.
  • Meiosis: reduces chromosome number by half, shuffles genes.

Meiosis

  • Two cell divisions (Meiosis I and Meiosis II).
  • Meiosis I: prophase 1 (crossing over), metaphase 1, anaphase 1, telophase 1.
  • Meiosis II: prophase II, metaphase II, anaphase II, telophase II. Results in 4 haploid daughter cells each with 23 single-stranded chromosomes.

Spermatogenesis Stages

  • Spermatogonia: divide by mitosis.
  • Type B spermatogonium: becomes primary spermatocyte.
  • Primary spermatocyte: undergoes meiosis I, produces secondary spermatocytes.
  • Secondary spermatocytes: undergo meiosis II, dividing into spermatids.
  • Spermatids: transform into spermatozoa (mature sperm) via spermiogenesis.

Spermatozoan

  • Head: contains haploid chromosomes and acrosome (enzymes for egg penetration).
  • Tail: middle piece (mitochondria), principal piece, endpiece.

Semen

  • Seminal fluid expelled during ejaculation composed primarily of seminal plasma.
  • Normal sperm count: 50-120 million/mL. Infertility: <20 million/mL.
  • Contains clotting enzymes, serine protease (PSA), fructose, citrate, prostaglandins.

Semen Composition and Motility

  • Stickiness comes from semenogelin.
  • Elevated pH (buffered by prostatic fluid) and energy source (fructose, citrate) are required for sperm motility.

Male Sexual Response

  • Four phases: excitement, plateau, orgasm, resolution.

Sexual Response Phases

  • Excitement: vasocongestion, myotonia, increased heart rate/blood pressure; erection due to parasympathetic stimulation and nitric oxide (NO).
  • Plateau: increased vasocongestion and myotonia.
  • Orgasm: emission (sperm propelled through ducts), expulsion (muscular contractions lead to ejaculation); sympathetic reflex constricts internal urethral sphincter.
  • Resolution: body variables return to normal; refractory period.

Neural Control of Sexual Response

  • Parasympathetic signals cause erection.
  • Sympathetic signals cause emission.
  • Somatic signals cause expulsion.