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24 September 2014
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Fact files

Organs - Male genitals

System: Reproductive

Location: Below the bladder and between the legs

Physical description: Plum sized testes and expandable sausage-like penis

Function: To make and deliver sperm into a woman

Testes produce sperm and male sex hormones

Sperm and male sex hormones are made in two plum sized glands called the testes.

The testes lie in a sac called the scrotum that hangs outside the body, between the legs. This arrangement maintains sperm at a temperature slightly below body temperature, which is essential for the production of healthy sperm.

Each testis has a long highly coiled tube attached to it known as an epididymis. Immature sperm pass out of the testes into the epididymes. As sperm make their way through these tubes, they mature and learn to swim. Maturation takes between one and three weeks, after which they are either ejaculated out of the body or reabsorbed into the body.

Every day a man makes between 50 and 500 million sperm.

The penis and erections

The penis is very sensitive and is partly covered by a loose fold of skin called the foreskin. Most of the penis is composed of spongy erectile tissue. When a man is sexually aroused, this spongy tissue fills with blood, causing the penis to enlarge and become rigid. This is known as an erection. An erection enables the penis to serve its role as the penetrating organ that delivers sperm into a woman's vagina.

Sperm and urine both leave the body through a tube called the urethra that runs down the middle of the penis.

Semen and ejaculation

Semen is a milky white, sticky mixture of sperm and fluid secretions. It provides nutrients to energise sperm and acts as a transport medium to carry sperm through the penis, out of the body and into a woman's vagina.

During ejaculation, sperm are propelled from the epididymis along a duct called the vas deferens (the coat hanger-shaped duct shown in the 3D image above). This carries sperm upwards, out of the scrotum, towards the penis. En route, fluids from the seminal vesicles (the small red glands at the end of the vas deferens shown in the 3D image above) and the prostate gland dilute the sperm. These fluids provide the optimal environment for sperm to swim and survive in the acidic conditions of the female reproductive tract.

At the last stage of ejaculation, semen passes into the urethra and out of the penis.

During ejaculation, a man produces between two and five millilitres of semen that contains between 50 and 130 million sperm per millilitre.

The tiny bulbourethral glands (shown in orange on the 3D image above) secrete a thick, clear mucus that drains into the urethra. This is the first secretion to pass down the urethra when a man becomes sexually excited. It is thought to clean the urethra before ejaculation and act as a lubricant during sex.

Male genitals become active at puberty

The male genitals are present in the body at birth, but they're not sexually active until adolescence. At puberty the testes, penis and scrotum begin to grow. The genitals are mature when the testes produce functional sperm

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