The penis is structured around a series of long tubular tissue structures known as erectile tissue. This spongy tissue is able to hold a large volume of blood to produce an erection necessary for sexual intercourse. The glans penis (or just glans for brevity) is actually an extension of this spongy material, covered with mucous membrane much like the lining of the mouth and the vagina.
This tissue is protectively covered by a tube of skin which, in it's natural state, extends from the body to cover the glans. This external covering is actually in two parts. At the preputial sphincter, also known as the frenar band, the external skin, which is basically the same type of skin which covers the rest of the body, connects to a different type of skin which is slightly mucousal in nature and which is rich in stretch receptor nerves. This skin 'rolls' under the outer skin and ends just behind the corona of the glans at the sulcus. This skin is very thin, sensitive and has elastic qualities. It is long enough to cover most of the penis when it is retracted (pulled back) and because of it's thin structure and elasticity, is capable of 'telescoping', or folding, over itself as it is moved back and forth, especially during sexual activity. The folding action is made possible by the texture of the inner foreskin which has a series of ridges or natural folding points in concentric circles, which hug the shaft and glans. This series of folds is called the ridged band and has the same characteristics of action as the inner and outer eyelids.
The nature of the inner foreskin is also such that it secretes sebum, natural oilsand emollients which serve to keep the glans moist and soft. After circumcision, the glans is no longer kept moist and soft and the skin becomes keratinized (dry and hard). This causes a decrease in the sensitivity of the nerves in the glans, since the transmission of pressure is more resistive. It is also now understood, that the frenar band, which is completely lost to circumcision, helps to keep the foreskin over the glans during nocturnal erections, to prevent the glans from becoming dry while exposed.