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Penis Anatomy & Histology
Here we will learn the anatomical details of the penis, which serves both reproductive and urinary functions.
Anatomical orientation is determined based upon the erect penis: the dorsal surface of faces the abdomen, and the ventral surface faces away from the abdomen.
The urethra transports both urine and semen to the external environment.
The prostate gland is inferior to the urinary bladder; that the portion of the urethra that travels through it is the prostatic urethra, which houses the openings for the ducts of the prostate gland and the openings of the ejaculatory duct.
The membranous urethra travels through the deep perineal pouch and perineal membrane.
The remainder of the urethra is called the spongy urethra; its distal opening is the external urethral orifice.
The bulbourethral glands (aka, Cowper’s glands) glands secrete lubricating mucus into the spongy urethra, cleansing and preparing it prior to the arrival of semen.
The urethral glands secrete mucus to clean and prepare the spongy urethra.
Deep fascia (aka Buck’s fascia) lies deep to the skin; it contains the erectile bodies, which are also wrapped in a fibrous connective tissue layer called tunica albuginea.
The spongy urethra travels in the ventral compartment; the corpus spongiosum surrounds it. The tunica albuginea of the corpus spongiosum is thinner than that of the corpus cavernosa, which prevents compression of the urethra.
The paired corpus cavernosa are dorsal; they are also wrapped in tunica albuginea and are incompletely separated by a septum.
The dorsal artery runs between the deep fascia and the tunica albuginea, and the deep arteries travel within the corpus cavernosa. The dorsal and deep arteries are branches of the internal pudendal artery.
The deep and superficial dorsal penis veins are separated by the deep fascia of the penis.
Be aware that the venous blood from the deep dorsal vein drains into the prostatic venous plexus, then the internal iliac veins, which connects with the vertebral venous plexus; this pathway explains why prostate cancer can metastasize to the vertebral venous plexus.
The deep arteries are inside the corpus cavernosa, but the deep veins are outside of them.
Though not shown, sensory innervation of the penis is supplied by a branch of the pudendal nerve called the dorsal nerve of the penis; autonomic innervation is supplied by the cavernous nerves, which arise from the pelvic plexus (aka the hypogastric plexus).
Erectile dysfunction is thus associated with impaired parasympathetics arising from spinal cord segments S2-S4.
A “fractured” penis occurs when the tunica albuginea tears, typically as a consequence of abrupt angling of an erect penis; swelling and bruising result.
Anatomical orientation
Coronal Section
Erectile bodies
Comprise vascular tissues that engorge with blood upon arousal.
The singular corpus spongiosum surrounds the urethra, and comprises the ventral erectile body.
The paired corpus cavernosa (singular = corpus cavernosum) comprise the dorsal erectile bodies.
The bulb of the corpus spongiosum anchors the penis to the perineal membrane; 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 motions during ejaculation.
The distal expansion of the corpus spongiosum is called the glans; the corona is the margin of the glans where it projects over the corpus cavernosum.
Te crura (singular = crus) of the corpus cavernosa extend laterally; they attach to the pubic arch of the pelvis and are wrapped in the ischiocavernosus muscles that force blood into the erectile tissues and maintains erection.
The root of the penis comprises both the crura of the corpus cavernosa and the bulb of the corpus spongiosum (and their associated muscles).
The shaft (aka, body) of the penis is the portion between the root and glans; it is the “free” portion of the penis.
Skin covers the shaft and glans of the penis, and label the prepuce (aka, foreskin), which is the double layer of skin that covers the glans; in the adult, it is retractable.
Male circumcision is the surgical removal of some or all of the prepuce, which leaves the glans exposed.
Cross Section