Penis

Penis

The male copulatory organ and the conduit for urine and semen, built from three cylinders of erectile tissue — two corpora cavernosa and the corpus spongiosum around the urethra — that become rigid when engorged with blood.

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Overview

The penis has a root fixed in the superficial perineal pouch — two crura (attached to the ischiopubic rami and covered by ischiocavernosus) and the bulb (attached to the perineal membrane and covered by bulbospongiosus) — and a free body ending in the glans. In the body, the paired corpora cavernosa lie dorsally and the corpus spongiosum, containing the spongy urethra, lies ventrally; the corpus spongiosum expands distally into the glans, whose rim is the corona. Each erectile body is wrapped in tunica albuginea (thick around the cavernosa, thin around the spongiosum), and all three are bound by the deep fascia of the penis (Buck fascia), then loose superficial (dartos) fascia and thin, mobile skin that forms the prepuce (foreskin) over the glans, attached by the frenulum. The suspensory and fundiform ligaments anchor the body to the pubic symphysis.

Erection is a neurovascular event: parasympathetic nitric oxide raises cGMP in cavernous smooth muscle, the helicine arteries and trabeculae relax, blood fills the sinusoids and the expanding corpora compress the outflow venules against the tunica albuginea (veno-occlusion). The thin tunica of the corpus spongiosum keeps it compressible, so the urethra stays open for ejaculation. Detumescence follows sympathetic vasoconstriction and breakdown of cGMP by phosphodiesterase-5.

Location: Attached to the pubic arch and perineal membrane (root) and hanging anterior to the scrotum (body).

Parts & subdivisions

Corpora cavernosa
Paired dorsal erectile bodies; principal source of rigidity.
Corpus spongiosum
Ventral erectile body containing the spongy urethra; forms the bulb and glans.
Glans and prepuce
Distal expansion of the corpus spongiosum, bearing the external urethral orifice; covered by the foreskin.
Root
Crura (with ischiocavernosus) and bulb (with bulbospongiosus) in the superficial perineal pouch.
Spongy urethra
≈15 cm; widens in the bulb and in the navicular fossa of the glans.

Anatomy

Innervation: Dorsal nerve of the penis (pudendal, S2–S4) — sensory to the glans and skin (penile block). Cavernous nerves (parasympathetic from the pelvic splanchnic nerves S2–S4, and sympathetic T12–L2) via the prostatic plexus. Ilioinguinal nerve to the skin of the root.
Arterial supply: Branches of the internal pudendal artery: deep (cavernosal) arteries in the corpora cavernosa giving helicine arteries (the main supply for erection); dorsal arteries (glans, skin and fascia, running in Buck fascia); arteries of the bulb (corpus spongiosum and bulbourethral glands). Superficial external pudendal arteries supply the skin.
Venous drainage: Cavernous spaces → deep dorsal vein (beneath Buck fascia; passes below the pubic symphysis into the prostatic venous plexus); skin → superficial dorsal vein → external pudendal → great saphenous vein.
Lymphatic drainage: Skin and prepuce → superficial inguinal nodes; glans → deep inguinal and external iliac nodes; erectile tissue and spongy urethra → internal iliac nodes.
Development: Genital tubercle (glans and body) and urethral folds (spongy urethra), under DHT; homologous to the clitoris (and the corpus spongiosum to the vestibular bulbs).

Function

Copulation and deposition of semen in the vagina.
Conduit for urine and semen (spongy urethra).

Physiology: Erection: parasympathetic (point). Emission: sympathetic (squeeze). Ejaculation: somatic pudendal reflex contracting bulbospongiosus and pelvic floor (shoot).

Clinical significance

Erectile dysfunction

Most often vascular (atherosclerosis — an early marker of cardiovascular disease), plus diabetes, neurological disease, pelvic surgery, hypogonadism, drugs (β-blockers, thiazides, SSRIs) and psychological causes. PDE5 inhibitors (sildenafil, tadalafil) are first-line and are contraindicated with nitrates (severe hypotension).

Priapism

Erection lasting >4 h unrelated to stimulation. Ischaemic (low-flow) priapism — sickle cell disease, intracavernosal drugs, antipsychotics, trazodone — is a painful emergency (aspiration, phenylephrine). Non-ischaemic (high-flow) follows arterial injury.

Hypospadias, phimosis and penile cancer

Hypospadias: ventral urethral meatus from incomplete fusion of the urethral folds (≈1 in 250 boys; avoid circumcision before repair). Phimosis/paraphimosis: non-retractile foreskin / retracted foreskin trapped behind the glans (emergency). Penile squamous-cell carcinoma: associated with HPV, phimosis, poor hygiene and lichen sclerosus; spreads to inguinal nodes.

Peyronie disease and penile fracture

Fibrous plaques of the tunica albuginea cause curvature and painful erection. Rupture of the tunica albuginea during forceful intercourse ("penile fracture") causes a crack, detumescence and haematoma — surgical repair.

Compiled from standard anatomy and physiology references — see the Reproductive System sources. For education only; not medical advice.