The male reproductive system consists of the testes (singular: testis), various accessory glands and a series of ducts which deliver the semen to the penis.

The paired testes are located in the scrotum and are responsible for spermatogenesis and production of testosterone. Each testis is divided into lobules containing the seminiferous tubules. It is within these tubules that the spermatozoa, immature sperm cells, are formed. Located between the seminiferous tubules are Leydig cells (interstitial cells) which produce testosterone. Sperm cells migrate from the seminiferous tubules through the rete testis to the epididymis on the superior aspect of the testes. Sperm cells mature within the epididymis and are stored there until ejaculation. Each mature sperm cell has a long tailpiece, a midsection, a neck and a head which contains the nuclear material. The head is covered with a cap-like structure called an acrosome.

At ejaculation, the sperm cells are forced into the paired vas deferens (ductus deferens) which run upward over the anterior aspect of the urinary bladder and then descend behind the bladder. Behind the bladder, each vas deferens widens into an ampulla and receives the secretions of the seminal vesicles. The paired vas deferens form the ejaculatory ducts which pass into the prostate gland and join the urethra. The urethra also receives the secretions of the prostate gland and the bulbourethral glands.

The urethra runs along the length of the penis to the glans, the head of the penis. The glans is covered by a fold of skin called the prepuce. In preparation for sexual intercourse, cavernous vascular tissue within the penis becomes engorged with blood, causing the penis to lengthen and become erect. There are three such bodies of vascular tissue running the length of the penis. These are the paired corpora cavernosa, which run along the dorsal surface of the penis, and the single corpus spongiosum which surrounds the urethra. The flow of blood into the cavernous tissue is normally restricted due to constriction of the deep arteries. During erotic arousal, an increase in parasympathetic stimulation causes relaxation of the arterial smooth muscle and so permits greater blood flow into the penis. As the arteries of the penis are derived from the internal iliac arteries and are strongly regulated by parasympathetic innervation, both vascular and neurological disorders may inhibit blood flow to the penis and so prevent erection.

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