Prostate

It is a walnut sized gland located at the base of the bladder, anterior to the seminal vesicles and rectum. Hence, it can be palpated during a PR or per-rectal examination. The prostatic urethra passes through it. It is composed of fibromuscular stromal and branching, tubuloalveolar glandular tissue. Both smooth and striated muscles are present in the prostatic stroma. It can be divided into five lobes - right and left lateral lobes, middle lobe and right and left posterior lobes. The glandular elements of the prostate are arranged in three zones - highly glandular peripheral zone, a central zone (with submucosal glands) and the periurethral or transitional zone. Benign prostatic hyperplasia occurs most commonly in the periurethral zone involving the lateral and middle lobes. Prostatic cancer involves the peripheral zones involving the posterior lobes. The prostate is surrounded by a true and false capsule.

The epithelium consists of secretory cells, neuroendocrine cells and basal cells. The secretory cells produce alkaline prostatic fluid which is composed of citric acid, prostatic acid phosphatase, prostaglandins, fibrinogen and prostate specific antigen or PSA. PSA liquefies semen after ejaculation, helping in motility of sperm. Calcified secretions called corpora amylacea can be identified in the lumen. Their number increases with age. The neuroendocrine cells are dendritic, regulatory cells. Neuron-specific enolase, chromogranin A, serotonin, PTH related peptide or PTHrP, calcitonin, somatostatin and bombesin have been identified in neuroendocrine cells. These cells play a role in the growth and differentiation of the prostate and regulation of secretions.

The prostate is supplied by the inferior vesical artery, internal pudendal and middle rectal artery. Lymphatic drainage is to the internal iliac nodes. Nerve supply is from the hypogastric plexus. The prostatic veins drain into the prostatic venous plexus, also called Santorini’s plexus, that is located between the capsular layers. It drains into the internal iliac veins. The prostatic plexus connects with the Batson’s vertebral plexus which increases the risk of prostatic carcinoma spreading into the vertebral column.

Bulbourethral glands

Also called Cowper’s glands, they lie lateral to the membranous urethra. It opens into the penile urethra. The Cowper’s glands are composed of multiple lobules of tubuloalveolar glands lined by simple cuboidal epithelium. It secretes a thick, mucus-like lubricating fluid that forms the pre-ejaculate.

Penis

The penis consists of a fixed root that lies in the superficial perineal space and a pendulous body that lies in the scrotum. The root is made of three masses of erectile tissue- the bulb in the middle and two laterally placed crura. The bulb is attached to the perineal membrane while the crura are fixed to the pubic arch. The bulbar urethra lies in the bulb of the penis. The body of the penis is composed of three elongated masses of erectile tissue - two corpora cavernosa that are continuations of the crura and a middle corpus spongiosum that continues from the bulb. The corpus spongiosum is expanded distally into the glans penis. The external urethral meatus lies at the tip of the glans penis while the penile urethra runs in the corpus spongiosum. The skin covering the glans is called prepuce or foreskin, it is attached to the glans by a fold of skin called the frenulum. It is the prepuce or foreskin that is removed during circumcision. The deep fascial covering of the body of the penis is called Buck’s fascia. It is continuous with Scarpa’s fascia of the anterior abdominal wall. Apart from that, there is a separate fascial covering for each of the erectile masses called the tunica albuginea. The penis is suspended from the pubic symphysis by the suspensory ligament.

The penis has a rich blood supply. The artery of the bulb of the penis supplies the corpus spongiosum. It is a branch of the internal pudendal artery. The deep arteries of the penis supply the two corpora cavernosa. They too arise from the internal pudendal artery. Another terminal branch of the internal pudendal artery is the dorsal artery of the penis that runs along the dorsal surface of the penis and supplies the skin and glans penis. Venous drainage is by superficial and deep dorsal veins. The superficial vein drains the skin and prepuce and drains into the superficial external pudendal vein. The deep vein drains the glans penis, corpora cavernosa and corpus spongiosum and drains into the prostatic venous plexus. It also communicates with the internal pudendal veins. Lymphatic drainage is noteworthy - the skin and prepuce drain into the superficial inguinal nodes; glans penis drains to the deep inguinal node (Cloquet’s gland) and external iliac nodes while the deeper tissues like the penile urethra and erectile tissues drain into the internal iliac nodes.

Somatic innervation to the skin of the body, prepuce and glans is by the dorsal nerve of the penis a branch of the pudendal nerve. Parasympathetic supply is from the pelvic splanchnic nerves (S2-4) through cavernous nerves coming from the prostatic plexus. Parasympathetic stimulation leads to vasodilation and penile engorgement. Sympathetic supply is derived from T1 to L1 spinal segment via the inferior hypogastric plexus. Sympathetic stimulation leads to ejaculation by smooth muscle activation in the ductal system of the male reproductive tract.

Nerve supply and lymphatic drainage of the scrotum

The scrotum drains to the superficial inguinal lymph nodes. Anterior part of the scrotal skin is supplied by the ilioinguinal nerve and genital branch of the genitofemoral nerve (L1) while posteriorly, the skin of the scrotum is supplied by the posterior scrotal nerves and perineal branch of the posterior cutaneous nerve of the thigh (S3).