The male reproductive system is a fascinating arrangement of external and internal genital organs that are intimately connected to the male urinary tract through the penis externally and the urethra internally. The penis is the largest part of the external male genitalia and is made up of three main parts:
- the root
- the body
- the glans penis
The root of the penis consists of:
- the median urethral bulb
- the crura, one on either side
Each crus is covered by the Ischiocavernosus, while the bulb is surrounded by the bulbocavernosus. The root of the penis lies in the perineum, between the inferior fascia of the urogenital diaphragm and the fascia of Colles. In addition to being attached to the fasciæ and the pubic rami, it is bound to the front of the symphysis pubis by the fundiform and suspensory ligaments.
The body of the penis stems from the superficial perineal space where it is attached to the perineal membrane. It is made up of three masses of erectile tissue, which include the paired corpora cavernosa and the corpus spongiosum. These three sections of the shaft of the penis are cylindrical in shape and are individually covered by the fibrous tunica albuginea internally and Buck’s fascia externally. The latter is continuous above with the fascia of Scarpa, and below with the dartos tunic of the scrotum and the fascia of Colles. The skin of the penis connects to this fascia through the loose areolar connective tissue.
The corpora cavernosa curve laterally to form the crura of the penis, to which the ischiopubic ramus is attached to, just in front of the ischial tuberosity. The two muscles which associate with the erectile bodies are the bulbospongiosus muscles and the ischiocavernosus muscle. The bulbospongiosus muscle attaches proximally to the perineal body and also to the proximal surface of the bulb of the penis. Its distal attachment is to the corpus spongiosus and it helps to compress the bulb of the penis, force blood into an erect penis and compress the outflow veins. The ischiocavernosus muscle originates from the inferior internal surface of the ischiopubic ramus and the ischial tuberosity and inserts onto the crus of the penis. It aids erection by increasing blood flow and preventing outflow.
The glans penis is the most distal portion of the corpus spongiosum and expands laterally at the distal aspect of the body of the penis, before narrowing at the very tip. It forms a bulbous shape and part of the bulb of the penis. It is covered by a double layer of skin and connective tissue, which extends from the neck of the glans to just beyond the tip of the penis and is known as the foreskin or prepuce.
All the lymphatic vessels of the penis pass to the superficial inguinal lymph nodes by accompanying the external pudendal blood vessels. The lymphatic vessels of the glans penis enter the deep inguinal lymph nodes and the external iliac lymph nodes. Their efferent vessels pass to the lateral aortic lymph nodes. From these nodes, efferents issue to the lumbar lymph trunk. The lumbar lymph trunks enter the cisterna chyli. Cisterna chyli drains into thoracic duct that drains into junction of the left subclavian vein and left internal jugular vein.
The innervation of the penis is handled by three major nerves:
- The skin and the glans penis are supplied by the dorsal nerve of the penis, which stems from the pudendal nerve and travels the length of the penis, beneath the deep fascia.
- The skin of the proximal part of the body of the penis is supplied by the ilioinguinal nerve.
- Finally, the erectile function is controlled by the parasympathetic nervous system; the pelvic splanchnic nerves in particular.
Blood Supply and Venous Drainage
The arterial supply of the penis includes the dorsal arteries of the penis, which are a continuation of the internal pudendal arteries, as are the deep arteries of the penis and the artery of the bulb of the penis. The external pudendal artery supplies the skin of the penis.
The venous drainage of the penis is controlled by the deep dorsal vein of the penis, which drains to the prostatic venous plexus and then on to the internal iliac or internal pudendal veins. Also, the superficial dorsal vein of the penis drains into the superficial external pudendal vein, a tributary of the great saphenous vein.