Penis Anatomy & Histology
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.
- Covered in tunica albuginea
- Comprise vascular tissues that engorge with blood upon arousal.
- 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,
- 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.
- 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.
- During an erection, parasympathetic stimulation dilates the helicine arteries and the venous sinuses become engorged, blocking venous drainage.
Embryology
External Genitalia