Male Genitalia: Anatomy and Function

• The male genitalia are the male reproductive organs
• Located both inside and outside the pelvis
• Consists of:
  • Testes
  • Epididymis
  • Vas deferens
  • Seminal vesicles
  • Ejaculatory ducts
  • Prostate gland
  • Bulbourethral glands
  • Penis
  • Scrotum

Scrotum

• A sac of skin and superficial fascia
• Hangs inferiorly exterior to the abdominopelvic cavity at the root of the penis
• Contains the testes and epididymis
• The skin is heavily pigmented and has numerous sebaceous glands
• Dartos muscle:
  • A layer of smooth muscle in the superficial fascia
  • Responsible for wrinkling the scrotal skin
  • Elevates the testes
• Cremaster muscles:
  • Bands of skeletal muscle arise from the internal oblique muscles of the trunk
  • Elevate the testes

Testes

• Paired, oval-shaped male reproductive organs
• Produce sperm and male sex hormones (testosterone)
• Located in the scrotum
• Tunica vaginalis:
  • The outer two-layered tunic
  • Derived from the peritoneum
• Tunica albuginea:
  • The fibrous capsule of the testis
  • Septa extending inward from the tunica albuginea divide the testis into lobules
  • The lobules contain seminiferous tubules

Seminiferous Tubules

• Highly coiled tubes
• The site of sperm production (spermatogenesis)
• Seminiferous tubules converge to form the tubulus rectus
• Straight tubulus rectus conveys sperm into the rete testis

Rete Testis

• A tubular network on the posterior side of the testis
• Sperm leave the testis through efferent ductules which enter the epididymis

Epididymis

• An elongated structure cups the posterior aspect of the testis
• Sperm mature and are stored here
• Consists of the head, body, and tail
• The duct is about 6 m long and tightly coiled
• During ejaculation, the epididymis contracts, expelling sperm into the ductus deferens

Ductus Deferens (Vas Deferens)

• Part of the spermatic cord
• Carries sperm from the epididymis to the ejaculatory duct
• Passes through the inguinal canal into the pelvic cavity
• Terminates by joining with the duct of the seminal vesicle to form the ejaculatory duct
• The vas deferens can contract to help move sperm

Spermatic Cord

• A collection of structures that run to and from the testes
• Encloses:
  • Ductus deferens
  • Testicular blood vessels
  • Nerves
• Passes through the inguinal canal

Inguinal Canal

• An oblique passageway in the anterior abdominal wall
• It transmits the spermatic cord in males
• Transmits the round ligament of the uterus in females

Ejaculatory Duct

• Formed by the union of the ductus deferens and the duct of the seminal vesicle
• Passes through the prostate gland
• Empties into the urethra

Urethra

• Transports urine and semen (at different times)
• Extends from the urinary bladder to the external urethral orifice
• Has three regions:
  • Prostatic urethra: within the prostate gland
  • Membranous urethra: passes through the urogenital diaphragm
  • Spongy (penile) urethra: runs through the penis and opens at the external urethral orifice

Seminal Vesicles

• Located on the posterior bladder surface
• Secrete seminal fluid, which contributes to semen volume
• Seminal fluid contains:
  • Fructose (energy source for sperm)
  • Prostaglandins (stimulate uterine contractions)
  • Vesiculase (coagulating agent)

Prostate Gland

• A doughnut-shaped gland that encircles the prostatic urethra
• Secretes prostatic fluid, which contributes to semen volume
• Prostatic fluid contains:
  • Citrate (nutrient source)
  • Enzymes (PSA, fibrinolysin)
• Acts to activate sperm

Bulbourethral Glands (Cowper's Glands)

• Pea-sized glands inferior to the prostate gland
• Produce a thick, clear mucus prior to ejaculation
• The mucus:
  • Neutralizes traces of acidic urine in the urethra
  • Lubricates the urethra and tip of the penis

Penis

• The male organ of copulation
• Delivers sperm into the female reproductive tract
• Consists of:
  • Root: attached proximal part
  • Shaft (body): the mobile part
  • Glans penis: the distal expanded end

Prepuce (Foreskin)

• A cuff of skin covering the glans penis
• Often removed by circumcision

Erectile Tissue

• Spongy connective tissue containing vascular spaces
• The penis contains three cylindrical bodies of erectile tissue:
  • Corpus spongiosum: surrounds the spongy urethra
  • Corpora cavernosa: paired dorsal cylinders

Erection

• During sexual arousal, the erectile tissue fills with blood
• This causes the penis to enlarge and become rigid
• Erection is initiated by parasympathetic reflexes

Semen

• A milky white mixture of sperm and accessory gland secretions
• Contains nutrients (fructose, citrate), protects and activates sperm, and facilitates their movement
• Prostaglandins in semen stimulate the uterus
• The alkalinity of semen neutralizes the acidity of the male urethra and female vagina, enhancing sperm motility
• Semen contains seminalplasmin, an antibiotic chemical that destroys certain bacteria
• Only 2-5 ml of semen are ejaculated, containing 20-150 million sperm/ml

Male Perineum

• Diamond-shaped region between the pubic symphysis, coccyx, and ischial tuberosities
• It suspends the scrotum and contains the root of the penis and anus