Prostate

Prostate

The prostate is a walnut-sized gland located at the base of the bladder, anterior to the seminal vesicles and rectum. Because of this position, it can be palpated during a PR (per-rectal) examination. The prostatic urethra passes through the gland.

The prostate is composed of fibromuscular stroma and branching tubuloalveolar glandular tissue. Both smooth and striated muscle are present in the prostatic stroma.

It can be divided into five lobes:

• Right and left lateral lobes
• Middle lobe
• Right and left posterior lobes

The glandular elements are arranged into three zones:

• Peripheral zone (highly glandular)
• Central zone (with submucosal glands)
• Periurethral (transitional) zone

Clinical correlations:

• Benign prostatic hyperplasia occurs most commonly in the periurethral zone, involving the lateral and middle lobes.
• Prostatic cancer involves the peripheral zone, involving the posterior lobes.

The prostate is surrounded by a true capsule and a false capsule.

The epithelium consists of secretory cells, neuroendocrine cells, and basal cells. Secretory cells produce alkaline prostatic fluid, which contains citric acid, prostatic acid phosphatase, prostaglandins, fibrinogen, and prostate-specific antigen (PSA). PSA liquefies semen after ejaculation, which helps sperm motility.

Calcified secretions called corpora amylacea can be seen in the lumen, and their number increases with age.

Neuroendocrine cells are dendritic regulatory cells. The following have been identified in neuroendocrine cells: neuron-specific enolase, chromogranin A, serotonin, PTH-related peptide (PTHrP), calcitonin, somatostatin, and bombesin. These cells contribute to growth and differentiation of the prostate and help regulate secretions.

Blood supply is from the inferior vesical artery, internal pudendal artery, and middle rectal artery. Lymphatic drainage is to the internal iliac nodes. Nerve supply is from the hypogastric plexus.

Prostatic veins drain into the prostatic venous plexus (Santorini’s plexus), located between the capsular layers, and then into the internal iliac veins. The prostatic venous plexus connects with Batson’s vertebral plexus, which increases the risk of prostatic carcinoma spreading to the vertebral column.

Bulbourethralglands

The bulbourethral glands (Cowper’s glands) lie lateral to the membranous urethra. They open into the penile urethra.

Cowper’s glands are composed of multiple lobules of tubuloalveolar glands lined by simple cuboidal epithelium. They secrete a thick, mucus-like lubricating fluid that forms the pre-ejaculate.

Penis

The penis consists of:

• A fixed root in the superficial perineal space
• A pendulous body in the scrotum

The root is made of three masses of erectile tissue:

• The bulb (midline)
• Two crura (lateral)

The bulb is attached to the perineal membrane, and the crura are fixed to the pubic arch. The bulbar urethra lies within the bulb.

The body of the penis is composed of three elongated masses of erectile tissue:

• Two corpora cavernosa (continuations of the crura)
• One corpus spongiosum (continuation of the bulb)

The corpus spongiosum expands distally to form the glans penis. The external urethral meatus is at the tip of the glans, and the penile urethra runs within the corpus spongiosum.

The skin covering the glans is the prepuce (foreskin). It is attached to the glans by a fold of skin called the frenulum. The prepuce (foreskin) is removed during circumcision.

The deep fascial covering of the body of the penis is Buck’s fascia, which is continuous with Scarpa’s fascia of the anterior abdominal wall. Each erectile mass also has its own fascial covering 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 supplies the corpus spongiosum (branch of the internal pudendal artery).
• The deep arteries of the penis supply the corpora cavernosa (also from the internal pudendal artery).
• The dorsal artery of the penis is another terminal branch of the internal pudendal artery; it runs along the dorsal surface and supplies the skin and glans.

Venous drainage occurs via superficial and deep dorsal veins:

• The superficial dorsal vein drains the skin and prepuce and drains into the superficial external pudendal vein.
• The deep dorsal vein drains the glans, corpora cavernosa, and corpus spongiosum and drains into the prostatic venous plexus. It also communicates with the internal pudendal veins.

Lymphatic drainage:

• Skin and prepuce  superficial inguinal nodes
• Glans penis  deep inguinal node (Cloquet’s gland) and external iliac nodes
• Deeper tissues (penile urethra and erectile tissues)  internal iliac nodes

Innervation:

• Somatic innervation to the skin of the body, prepuce, and glans is via the dorsal nerve of the penis (branch of the pudendal nerve).
• Parasympathetic supply is from the pelvic splanchnic nerves (S24) via cavernous nerves from the prostatic plexus; parasympathetic stimulation causes vasodilation and penile engorgement.
• Sympathetic supply is from T1 to L1 spinal segments via the inferior hypogastric plexus; sympathetic stimulation causes ejaculation by activating smooth muscle 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.

Innervation of the scrotal skin:

• Anterior scrotum: ilioinguinal nerve and genital branch of the genitofemoral nerve (L1)
• Posterior scrotum: posterior scrotal nerves and the perineal branch of the posterior cutaneous nerve of the thigh (S3)