Penis

The penis is the most distal part of the male urogenital system.

Gross anatomy

The gross anatomy of the penis can be broken into five sections: 

Skin

• loosely connected to the tunica albuginea

• distally folded to form the prepuce (foreskin) at the corona of the penis
• the internal layer of the prepuce is continuous with the neck and continues over the glans to the external urethral orifice
• the frenulum is a median fold of the skin at the urethral aspect of the glans running between the orifice and the deep surface of the prepuce

Root

• consists of three cylindrical structures of erectile tissue:
  • penile cura (paired) attach to the pubic arch. These join towards the symphyseal border and continue as the corpus cavernosum.
  • the bulb of the penis is (unpaired) found between the cura and is attached to the perineal membrane. It narrows to continue as the corpus spongiosum. The urethra pierces its deep aspect to traverse the bulb as the bulbar urethra and continue to the corpus spongiosum.

Body

• consists of three erectile structures, which are continuations of the structures described above -  right and left corpus cavernosum and median corpus spongiosum.
• during an erection, this part is capable of enlargement whenthese cylinders become engorged with blood.
• two suspensory ligaments support the body - fundiform and triangular ligaments.

Corpus cavernosum

• paired structure, and is encased in the tunica albuginea but are separated by a median fibrous septum

• the urethral aspect has a wide groove where the corpus spongiosum lies
• a dorsal groove houses the deep dorsal vein
• ends distally at the proximal part of the glans penis

Corpus spongiosum

• lies in the groove of the corpus cavernosum

• contains the penile part of the urethra (continuation of the bulbar part of the urethra), being approximately 15cm in length
• cylindrical in shape and expands distally to become the glans penis. The glans curves dorsally over the distal corpus cavernosum. The corona glandis projects from the base of the glans and contain multiple preputial glands (as well as on the penile neck) which secrete sebaceous smegma.

Blood supply

Arterial

• perineal artery

  • branch of the internal pudendal artery
  • (together with the posterior scrotal and inferior rectal arteries) supplies the tissues between the anus and penile bulb
• artery of the bulb of the penis
  • supplies the corpus spongiogum and the bulbourethral gland
• cavernosal artery (deep artery of the penis)
  • terminal branch of the internal pudendal artery
  • divide within the trabeculae of the corpus cavernosum to either end in capillary networks or branch into helicine arteries (most seen in the posterior region of the corpus cavernosum).
  • erection is caused by a rapid flow from the helicine arteries into the corpus cavernosum. This distension further contributes to the erection as the venous outflow is obstructed.
• dorsal artery of the penis
  • terminal branch of the internal pudendal artery
  • supplies the corpus spongiosum
  • supplies penile skin by some branches coursing through the dartos layer
  • supplies the tunica albuginea of the corpus cavernosum via a circumflex branch that courses around the shaft of the penis

Venous

• deep dorsal vein (unpaired) drains the corpus cavernosum and corpus spongiosum
• superficial dorsal vein (unpaired) drains the prepuce and penile skin

Nerve supply

Pudendal nerve and pelvic plexuses (S2-4)

Lymphatic drainage

• penile skin: accompanies the external pudendal vessels to the superficial inguinal nodes
• glans: to deep inguinal and external iliac nodes
• erectile tissue and penile urethra: to internal iliac lymph nodes

Development

Arises from the genital tubercle (from the cranial end of the cloacal membrane), which lengthens to form the phallus (male and female). This then further lengthens to form the penis in males.

Variant anatomy

• hypospadias
• phleboliths in the corpus cavernosum

Related pathology

• Fracture of penis
• Urethral strictures
• Squamous cell carcinoma of the penis (staging)