Body of the penis
Diagram of penis. Body (labeled as shaft) at the top.
The constituent cavernous cylinders of the penis.
Details
Precursor	Genital tubercle
Part of	Penis
System	Genitourinary
Artery	Deep artery, dorsal artery
Vein	Dorsal veins
Nerve	Dorsal nerve, cavernous nerves
Lymph	Superficial inguinal lymph nodes, internal iliac lymph nodes
Identifiers
Latin	corpus penis
TA98	A09.4.01.003
TA2	3664
FMA	18249
Anatomical terminology [edit on Wikidata]

The body or shaft of the penis is the free portion of the human penis that is located outside of the pelvic cavity. It is the suspended middle portion of the organ, continuous proximally with the internal root and distally with the glans. Unlike the root, the body contains no muscle, consisting mostly of the corpora cavernosa, the corpus spongiosum and the spongy urethra, together with supporting skin, connective tissue, blood and lymphatic vessels and fascia.^[1] The corpora cavernosa are intimately bound to one another with a dorsally fenestrated septum, which becomes a complete one before the penile crura.^[2] The body of the penis is homologous to the female clitoral body.^[3][4][5]

Structure

The body of the penis is suspended from the pubic symphysis by the suspensory ligament, part of the deep fascia arising from the anterior surface of the symphysis.^[1] It has two surfaces; the dorsal and the ventral or urethral. The penile raphe runs on its ventral surface.

The body is surrounded by a bi-layered model of tunica albuginea in which a distal ligament buttresses the glans penis and plays an integral role in the penile fibroskeleton, and the structure is called "os analog", a term coined by Geng Long Hsu in the Encyclopedia of Reproduction.^[2] The human penis differs from those of most other mammals in having no baculum (or erectile bone), relying exclusively on engorgement with blood to reach its erect state; the loss of the baculum in the human lineage has been linked to changes in mating pattern.^[6]

A shallow groove, which marks their junction on the upper surface lodges the deep dorsal vein of the penis, which is flanked by a pair of cavernosal veins of the penis,^[2] while a deeper and wider groove between them on the surface below contains the corpus spongiosum. The body is ensheathed by fascia, which includes tunica albuginea, Buck's fascia, dermis, and skin.

Development

The penis derives from the genital tubercle, which develops into the phallus under the influence of androgens from the testis. Elongation draws the urethral folds forward to form the lateral walls of the urethral groove, whose epithelial lining becomes the urethral plate. The penile urethra is formed when the urethral folds enclose this plate, a process usually complete towards the end of the third month; the most distal part of the urethra forms at the end of the fourth month. Fusion of the two urethral folds gives rise to the spongy body, and two cavernous bodies arise above it to become the corpora cavernosa.^[1]

Function

Erection occurs through parasympathetic innervation, which allows engorgement of the corporal bodies; the bulbospongiosus and ischiocavernosus muscles at the root compress the veins and prevent blood draining from the corpora cavernosa. Following ejaculation, sympathetic stimulation constricts the coiled helicine arteries and the two muscles relax, allowing the cavernous spaces to drain and the penis to become flaccid.^[1] The strength and inflexibility of the tunica albuginea covering the corpora blocks venous return and is therefore responsible for maintaining rigidity during an erection.^[8]

Clinical significance

Erectile dysfunction, the inability to achieve or maintain an erection, is the most common disorder of the penis, and most commonly results from vascular disease.^[1]

Penile fracture is a rupture of the tunica albuginea caused by severe blunt trauma to the erect penis, which raises cavernosal pressure beyond what the tunica can withstand. Most cases occur during sexual intercourse. During erection the circular fibres of the tunica thin from around 2 mm to about 0.25 mm, and the weakest point lies on the ventral side of the shaft immediately adjacent to the urethra, where most ruptures occur; the urethra is involved in roughly 20% of cases. Buck's fascia normally confines the resulting haematoma and swelling to the penile shaft. Penile fracture is regarded as a urological surgical emergency, as delayed treatment can result in long-lasting sexual dysfunction.^[8]

In Peyronie's disease, fibrous plaques containing excessive collagen form within the tunica albuginea, causing focal inelasticity and curvature of the penis. The condition is usually benign but may be associated with painful erections or erectile dysfunction. Its underlying pathogenesis is not known, although evidence suggests that repeated microtrauma leads to fibrin deposition from microvascular injury.^[1]

Priapism is a prolonged, rigid erection occurring in the absence of appropriate stimulation, conventionally defined as one lasting four hours or longer and not relieved by ejaculation. The ischaemic form is a urological emergency: if left untreated, damage to the corporal tissue progresses to necrosis and then fibrosis, resulting in penile shortening and permanent erectile dysfunction.^[9]

See also

• Human penis
• Root of penis
• Glans penis
• Foreskin
• Media related to Human penis at Wikimedia Commons

Additional images

• 
  Dissection of the male human genitalia
• 
  Labeled image of the male human genitalia. The body of the penis is labeled as "Shaft".

References

This article incorporates text in the public domain from page 1249 of the 20th edition of Gray's Anatomy (1918)