Main Model
Cavernous body of penis
Penis
The penis is the male copulatory organ and, by conveying the urethra, provides the common outlet for urine and semen. The penis consists of a root, body, and glans. It is composed of three cylindrical cavernous bodies of erectile tissue: the paired corpora cavernosa dorsally and the single corpus spongiosum ventrally. In the anatomical position, the penis is erect; when the penis is flaccid, its dorsum is directed anteriorly. Each cavernous body has an outer fibrous covering or capsule, the tunica albuginea. Superficial to the outer covering is the deep fascia of the penis (Buck fascia), the continuation of the deep perineal fascia that forms a strong membranous covering for the corpora cavernosa and corpus spongiosum, binding them together. The corpus spongiosum contains the spongy urethra. The corpora cavernosa are fused with each other in the median plane, except posteriorly where they separate to form the crura of the penis. Internally, the cavernous tissue of the corpora is separated (usually incompletely) by the septum penis.
The root of the penis, the attached part, consists of the crura, bulb, and ischiocavernosus and bulbospongiosus muscles. The root is located in the superficial perineal pouch, between the perineal membrane superiorly and the deep perineal fascia inferiorly. The crura and bulb of the penis consist of erectile tissue. Each crus is attached to the inferior part of the internal surface of the corresponding ischial ramus, anterior to the ischial tuberosity. The enlarged posterior part of the bulb of the penis is penetrated superiorly by the urethra, continuing from its intermediate part.
The body of the penis is the free pendulous part that is suspended from the pubic symphysis. Except for a few fibers of the bulbospongiosus near the root of the penis and the ischiocavernosus that embrace the crura, the body of the penis has no muscles.
The penis consists of thin skin, connective tissue, blood and lymphatic vessels, fascia, the corpora cavernosa, and corpus spongiosum containing the spongy urethra. Distally, the corpus spongiosum expands to form the conical glans penis, or head of the penis. The margin of the glans projects beyond the ends of the corpora cavernosa to form the corona of the glans. The corona overhangs an obliquely grooved constriction, the neck of the glans, which separates the glans from the body of the penis. The slit-like opening of the spongy urethra, the external urethral orifice (meatus), is near the tip of the glans penis.
The skin of the penis is thin, darkly pigmented relative to adjacent skin, and connected to the tunica albuginea by loose connective tissue. At the neck of the glans, the skin and fascia of the penis are prolonged as a double layer of skin, the prepuce (foreskin), which in uncircumcised males covers the glans penis to a variable extent. The frenulum of the prepuce is a median fold that passes from the deep layer of the prepuce to the urethral surface of the glans.
The suspensory ligament of the penis is a condensation of deep fascia that arises from the anterior surface of the pubic symphysis. The ligament passes inferiorly and splits to form a sling that is attached to the deep fascia of the penis at the junction of its root and body. The fibers of the suspensory ligament are short and taut, anchoring the erectile bodies of the penis to the pubic symphysis.
The fundiform ligament of the penis is an irregular mass or condensation of collagen and elastic fibers of the subcutaneous tissue that descends in the midline from the linea alba anterior to the pubic symphysis. The ligament splits to surround the penis and then unites and blends inferiorly with the dartos fascia forming the scrotal septum. The fibers of the fundiform ligament are relatively long and loose and lie superficial (anterior) to the suspensory ligament.
Arterial Supply of Penis
The penis is supplied mainly by branches of the internal pudendal arteries.
• Dorsal arteries of the penis run on each side of the deep dorsal vein in the dorsal groove between the corpora cavernosa, supplying the fibrous tissue around the corpora cavernosa, the corpus spongiosum and spongy urethra, and the penile skin.
• Deep arteries of the penis pierce the crura proximally and run distally near the center of the corpora cavernosa, supplying the erectile tissue in these structures.
• Arteries of the bulb of the penis supply the posterior (bulbous) part of the corpus spongiosum and the urethra within it as well as the bulbo-urethral gland.
In addition, superficial and deep branches of the external pudendal arteries supply the penile skin, anastomosing with branches of the internal pudendal arteries.
The deep arteries of the penis are the main vessels supplying the cavernous spaces in the erectile tissue of the corpora cavernosa and are, therefore, involved in the erection of the penis. They give off numerous branches that open directly into the cavernous spaces. When the penis is flaccid, these arteries are coiled, restricting blood flow; they are called helicine arteries of the penis (Greek helix, a coil).
Venous Drainage of Penis
Blood from the cavernous spaces is drained by a venous plexus that joins the deep dorsal vein of the penis in the deep fascia. This vein passes between the laminae of the suspensory ligament of the penis, inferior to the inferior pubic ligament and anterior to the perineal membrane, to enter the pelvis, where it drains into the prostatic venous plexus. Blood from the skin and subcutaneous tissue of the penis drains into the superficial dorsal vein(s), which drain(s) into the superficial external pudendal vein. Some blood also passes to the internal pudendal vein.
Innervation of Penis
The nerves derive from the S2-S4 spinal cord segments and spinal ganglia, passing through the pelvic splanchnic and pudendal nerves, respectively. Sensory and sympathetic innervation is provided primarily by the dorsal nerve of the penis, a terminal branch of the pudendal nerve, which arises in the pudendal canal and passes anteriorly into the deep perineal pouch. It then runs to the dorsum of the penis, where it runs lateral to the dorsal artery. It supplies both the skin and glans penis. The penis is richly supplied with a variety of sensory nerve endings, especially the glans penis. Branches of the ilio-inguinal nerve supply the skin at the root of the penis. Cavernous nerves, conveying parasympathetic fibers independently from the prostatic nerve plexus, innervate the helicine arteries of the erectile tissue.