Human Anatomy - Kotsan I. Y. 2009

Urogenital System
Genitalia - External Male Genitalia
Penis

The External Male Genitalia (organa genitalia masculina externa) include the Penis and the Scrotum.

The penis serves to discharge urine from the Urinary Bladder and to ejaculate semen. It consists of a posterior fixed part—the ROOT of the penis (radix penis), which attaches to the anterior surface of the pubic bones—and an anterior mobile part—the body of the penis (corpus penis), which terminates in the glans penis (glans penis) (Fig. 178).

The glans penis has a cone-like shape that is slightly flattened from top to bottom. The posterior thickened margin of the glans is called the corona of the glans (corona glandis), which is separated from the body of the penis by a shallow groove known as the neck of the glans (collum glandis). At the apex of the glans lies the slit-like external urethral orifice.

The body of the penis has two surfaces: an anterior (superior) wider surface, called the dorsum of the penis (dorsum penis), and a posterior (inferior) narrower surface—the urethral surface (facies urethralis), to which the Urethra is applied from the inside. Externally, the body of the penis is covered by Skin that transitions superiorly into the skin of the pubic region and inferiorly into the skin of the scrotum. The skin of the penis is thin, delicate, and mobile; it is separated from the underlying fascia by loose Connective Tissue and thus shifts easily. Along the midline of the urethral surface, the skin forms the raphe of the penis (raphe penis), which continues posteriorly into the skin of the scrotum and Perineum. In the anterior part of the penis (in the region of the neck of the glans), the skin forms a well-defined circular fold—the prepuce or foreskin of the penis (preputium penis), which covers the glans and then transitions into the skin of the glans. Between the glans and the prepuce lies a space—the preputial cavity—which opens anteriorly through an orifice that exposes the glans penis when the prepuce is pulled back. The internal surface of the prepuce, as well as the glans, is covered by a thin, delicate, translucent skin that differs from the skin covering the body of the penis. Located within the skin of the inner surface of the prepuce and the corona of the glans are sebaceous preputial glands (gll. preputiales), which secrete smegma. A significant accumulation of smegma within the preputial sac due to poor personal hygiene can lead to inflammation of the prepuce and The Development of phimosis (narrowing of the preputial orifice). On the inferior aspect of the glans, the prepuce is connected to the glans by a longitudinal fold—the frenulum of the prepuce (frenulum preputii), which nearly reaches the external urethral orifice.

Fig. 178. Male penis (inferior and anterior views)

1 — glans penis; 2 — corona of the glans; 3 — prepuce of the penis; 4 — raphe of the penis; 5 — corpus spongiosum of the penis; 6 — deep transverse perineal Muscle; 7 — external anal sphincter; 8 — anus; 9 — root of the penis; 10 — bulb of the penis; 11 — ischiocavernosus muscle; 12 — corpora cavernosa of the penis; 13 — superficial and deep Fascia of the penis; 14 — body of the penis; 15 — General Integument (skin) of the penis; 16 — frenulum of the prepuce; 17 — external urethral orifice

The core of the penis is formed by three longitudinally arranged bodies: two corpora cavernosa and one corpus spongiosum.

The corpora cavernosa of the penis (corpora cavernosa penis) are two long, nearly cylindrical structures with tapered anterior and posterior ends. The glans penis caps their tapered anterior (inferior) ends like a mushroom cap. The posterior ends of both corpora cavernosa diverge, taper, and form the crura of the penis (crura penis), which attach to the inferior rami of the pubic bones. The corpora cavernosa are fused to each other along their medial surfaces and are enclosed by a common tunica albuginea of the corpora cavernosa (tunica albuginea corporum cavernosum), which forms the septum of the penis (septum penis) in the space between them. Corresponding to this septum, a groove for the dorsal vein of the penis is located on the upper surface, while a furrow lodging the corpus spongiosum of the penis runs along the lower surface.

The corpus spongiosum of the penis (corpus spongiosum penis) is considerably smaller in volume than the corpora cavernosa. It is covered by its own tunica albuginea of the corpus spongiosum (tunica albuginea corporis spongiosi) and is traversed throughout its entire length by the urethra. Unlike the corpora cavernosa, the corpus spongiosum is expanded at both of its ends, forming the bulb of the penis (bulbus penis) posteriorly and the glans penis anteriorly. On the posterior surface of the glans, There is a depression that accommodates the anterior ends of the corpora cavernosa.

The corpora cavernosa and corpus spongiosum of the penis consist of numerous connective tissue trabeculae that branch off from the tunica albuginea. The connective tissue of the trabeculae contains elastic and smooth muscle fibers. Interlacing with one another, the trabeculae form a system of thin-walled, interconnected compartments (cavernae). These compartments are vascular spaces lined with endothelium and filled with Blood. Erection occurs due to the accumulation of blood within these spaces, a process facilitated by the vascular supply of the penis. Blood is delivered to the corpora cavernosa primarily by the deep artery of the penis, which branches into vessels running along the trabeculae. In the flaccid state of the penis, these Arteries have a coiled course, which led to their designation as helical arteries (arteriae helicinae). During sexual arousal, the smooth Muscles of the trabeculae and helical arteries relax, directing blood into the spaces of the corpora cavernosa. The corpora cavernosa swell and become rigid (resulting in penile erection). During erection, as the spaces fill with blood, the venous walls are compressed, which prevents the outflow of blood from the vascular spaces.

All three bodies of the penis (the corpora cavernosa and corpus spongiosum) are enclosed by deep and superficial fascia (fascia penis profunda et fascia penis superficialis). On the dorsum of the penis closer to its root, the fascia is more prominent because the tendons of the bulbospongiosus and ischiocavernosus muscles of the urogenital Diaphragm blend into it at this site. Superficial to the superficial fascia lies the easily mobile skin. Only on the glans penis, where the subcutaneous Adipose tissue is absent and the skin directly adheres to the tunica albuginea, is the skin immobile. The penis is anchored by two ligaments: the fundiform ligament and the suspensory ligament of the penis. The deep fundiform ligament (lig. fundiforme) extends from the lower part of the Pubic Symphysis and blends into the tunica albuginea of the corpora cavernosa. Fibers of this ligament also penetrate into the scrotum, into its dartos tunic. The suspensory ligament of the penis (lig. suspensorium penis) originates from the superficial fascia of the abdomen in the region of the linea alba and blends into the superficial fascia of the penis.

Blood supply to the penis. The skin, fascia, and tunica albuginea of the penile bodies receive blood from the anterior scrotal arteries (Branches of the external pudendal arteries) and the dorsal artery of the penis. The corpora cavernosa and corpus spongiosum are supplied by the dorsal and deep Arteries of the penis (branches of the internal pudendal artery). Venous blood drains from the penis via the deep vein of the penis and the vein of the bulb of the penis into the venous plexus of the urinary bladder, as well as via the deep Veins OF THE penis into the internal pudendal vein.

Lymphatic vessels of the penis drain into the internal iliac and superficial inguinal Lymph Nodes.

The penis is innervated by branches of the pudendal nerve (sensory innervation), branches of the inferior hypogastric plexus (sympathetic innervation), and branches of the pelvic splanchnic nerves (parasympathetic innervation).