More information about the male genital tract

The testes and epididymis, together called the testicles, lie outside the body, contained in the scrotum. The testes has three main types of cell: germ cells which produce sperm, cells called Sertoli cells which nourish the sperm and regulate the effects of hormones produced by the pituitary (see more information on the brain in the head section), and Leydig cells which make the male hormone testosterone. After puberty the germ cells begin to divide and, by a process called spermatogenesis, produce mature spermatozoa, usually simply called sperm - which takes about 70 to 80 days, and occurs throughout the testis in structures called seminiferous tubules. These tubules drain into the epididymis, which is a highly coiled tube about 6 to 7 metres long when fully developed, lying behind the testis. This is connected to the vas deferens, a muscular tube which is the pathway to the prostate, where it opens together with the duct from the seminal vesicle as the ejaculatory duct. During orgasm the muscular walls of the vas deferens contract vigorously, expelling sperm into the prostatic urethra and thence to the penis. During ejaculation between two and six millilitres of ejaculate will be produced, with each millilitre containing between 20 and 200 million sperms. Sperm production continues throughout the whole of reproductive life, so men may remain fertile until old age.

The prostate consists of glands, fibrous tissue and muscle cells. It lies at the neck of the bladder, in front of the anterior wall of the rectum (through which it can be felt by the finger of an examining physician - an essential part of assessment of prostatic size and potential Cancer). The tube that conveys urine from the bladder to the penis - the urethra - passes through it, and receives the openings of a number of prostatic ducts together with the ejaculatory ducts. During ejaculation the prostate secretes a small amount of alkaline fluid which is thought to aid the progression of sperm. In youth and young adulthood it is relatively small: after the age of 40 it enlarges.

The seminal vesicles lie behind the prostate, one either side, and produce most of the fluid that makes up the ejaculate (which is why men who have had a vasectomy, where the vas deferens is divided and the ejaculate contains no sperm, notice little difference in the volume of semen they produce).

The penis consists of three spongy structures: two called corpora cavernosa lying side by side, and one underneath called the corpus spongiosum which contains the urethra, and which forms the glans (the head) of the penis. During sexual arousal, under the influence of nerves from the autonomic nervous system (see more information on nerves in the limbs section) these spongy structures become filled with blood at high pressure, producing an erection. The glans is covered by a hood of skin called the prepuce, or foreskin, which is removed at circumcision (usually performed for religious reasons).

At puberty the first change is an increase in the volume of the testicle, which starts at about 10 (when the testicular volume is around 4 cc) and continues till the age of 16, when the adult volume of roughly 15 - 20 cc has been attained. Sparse pubic and axillary (armpit) hair first appears at around 10 and achieves adult distribution by 16 - 17, when most boys will be starting to shave. The penis thickens and lengthens from the age of 11 to about 17 and erections (always present even in infancy) become more vigorous and frequent. The pubertal growth spurt starts later than girls, at around 11, but lasts longer - so males usually end up taller. These ages are, of course, variable between individuals, because each of us is an individual.