The penis is made up of the shaft and the head. The shaft contains three cylinders and a tube. The head of the penis is called the glans. The glans has an opening at its tip for the tube, the urethra, through which urine and the ejaculate pass.
A sleeve of outer skin and an inner soft mucosal lining cover the head of the penis. This is called the prepuce or foreskin. In babies the foreskin protects the glans and the opening in it from which the urine exits the body (urethral meatus). These structures are protected from the irritating and damaging effects of faeces, urine and even nappies. The foreskin has very sensitive nerve endings in it. These enhance sexual pleasure. During sexual intercourse the foreskin protects from chafing and provides a moveable sheath that allows easy sliding of the penis in the vagina. It protects the glans from trauma throughout life. It is normal for there to be a build-up of a white waxy substance called smegma under the foreskin. Although it is not dirt and is not harmful, it is important to clean under the foreskin to prevent a build-up of smegma. A section of the penis is actually buried in the body and the corpus cavernosa are anchored to the pubic bone.
In children, the foreskin is attached to the glans until about the age of 5. This is normal and the foreskin should not be forcibly pulled back as this will cause pain.
The underside of the penis head or glans is called the frenulum and it is the most sensitive part of the penis. Inside the penis there are two long cylinders called the corpora cavernosa, which sit side by side. They contain spongy vascular tissue which controls the hardness (rigidity) and softness (flaccidity) of the penis. A tough outer membrane, the tunica albuginea, surrounds these cylinders. A third cylinder, the corpus spongiosum, surrounds the urethra. Smooth muscles are found in the corpus cavernosa. The smooth muscles control blood flow in and out of the penis by either tensing, which restricts blood flow into the penis, or relaxing, which increases blood flow into the penis resulting in an erection.
Adapted from: The SASHA Guide to Erections and Erection Problems. Smart D. © Ronin-Do (Pty) Ltd 2004 and Know your manhood. Lissoos I. KYB Pocket Books 1984
Used with permission from the publishers