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Penis Anatomy & Histology

Penis Anatomy & Histology

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Key Function:
Conduct urine and semen to the outside environment.
Key Anatomical Features:
Skin
  • Prepuce covers glans, is retractable in the adult.
Vessels
  • Superficial dorsal vein and artery
  • Deep dorsal vein
  • Deep arteries within corpus cavernosa
Connective tissues
  • Deep fascia surrounds erectile bodies and binds them together
  • Intercavernous fascia separate corpora cavernosa from corpus spongiosum.
Erectile bodies
  • Covered in tunica albuginea
  • Comprise vascular tissues that engorge with blood upon arousal.
Singular corpus spongiosum surrounds the urethra:
  • Glans is distal expansion; corona is rim of glans
  • Bulb is the widened proximal end
  • The bulb anchors the corpus spongiosum to the perineal membrane (not shown);
  • The bulb is wrapped in the bulbospongiosum muscle, which contracts to: force blood into the erectile tissues, eject residual urine from the urethra,
and produce pulsatile movements during ejaculation.
Paired corpus cavernosa (singular = cavernosum)
  • Lie dorsal to corpus spongiosum
  • Crus (singular = crura) of the corpus cavernosa extend laterally
  • Crus attach to the pubic arch of the pelvis (not visible here), and are wrapped by ischiocavernosus muscles; like the bulbospongiosum, these muscles force blood into the erectile tissues.
Root
  • Comprises bulb and crus of penis
Shaft
  • Free, pendulous portion of penis between root and glans
Urethra
  • Conducts semen to external environment
  • Terminates at external urethral orifice
  • Urethral glands secrete mucus to protect urethra from urine
Anatomical orientation
  • Dorsal surface faces the torso
  • Ventral surface faces away from the torso.
Semen/Seminal Fluid:
Semen (aka, seminal fluid)
  • Comprises sperm and seminal plasma.
Sperm
  • Gametes (aka, sex cells), produced by the testes
Seminal plasma
  • Nourishes and protects the sperm
  • Produced and secreted by the seminal vesicles, bulbourethral glands, and urethral glands.
Origins of semen:
Bulbourethral glands (aka, Cowper's glands)
  • Secrete lubricating mucus prior to arrival of the rest of the semen into spongy urethra
Ampulla of ductus deferens
  • Drains sperm
Seminal vesicles
  • Drain viscous, sugary seminal plasma fluid
Ejaculatory duct
  • Where sperm and seminal vesicle secretions mix; merger of ductus deferens and seminal vesicle
Prostate gland
  • Secretes alkaline, enzyme-rich fluid that protects sperm
Ejaculate
  • Semen after it has been ejected from the urethra.
Clinical correlation
  • Male circumcision is the surgical removal of the some or all of the prepuce, which leaves the glans exposed.
  • A "fractured" penis occurs when the tunica albuginea tears, typically as a consequence of abrupt angling of an erect penis; swelling and bruising result.
Penis Histology:
  • Comprises three cylindrical bodies of erectile tissue:
    • The dorsal bodies are the corpus cavernosa; they are wrapped in a thick fibrous layer of tunica albuginea.
In histological sample of the corpus cavernosum, can see a helicine artery and a nearby venous sinus.
    • Ventral body is the corpus spongiosum; the penile urethra lies within it; has urethral glands of Littre, which secrete pre-ejaculatory mucus into the prostatic urethra.
The erectile bodies comprise fibroelastic connective tissue interspersed with smooth muscle and neurovascular structures; indicate the deep arteries within the corpus cavernosa, and the dorsal artery and veins dorsally.
  • During an erection, parasympathetic stimulation dilates the helicine arteries and the venous sinuses become engorged, blocking venous drainage.
Embryology
External Genitalia

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