Structure of the skin

The skin has two layers:

The epidermis is non-vascular and consists of stratified epithelium (Fig. 23.1). It is very thick, hard and horny on areas such as the palms of the hands and soles of the feet and is much thinner and softer over other parts, such as the trunk and the inner sides of the limbs. The epidermis has two layers or zones: the outer is the horny zone; the inner is the germinative zone (Fig. 23.2). The horny zone has three layers:

Fig. 23.1 Section of the skin.

Fig. 23.2 The epidermis.

The germinative zone, which is deeper, consists of two layers:

The surface scales are constantly being rubbed off by friction and are constantly renewed from below as the deep cells multiply and are driven up to the surface, developing into scales as they approach it. The epidermis has no blood supply and practically no nerve supply. It is nourished by lymph from the blood vessels in the underlying dermis. It is the epidermis that is raised in a blister, and the blister can, therefore, be snipped with scissors without causing any pain, to allow the lymph it contains to escape.

The corium is a tough elastic layer, which is very thick in the palms of the hands and soles of the feet and very thin in the eyelids. It consists of connective tissue with elastic fibres, blood vessels, lymphatic vessels and nerves. Numerous conical projections, called papillae, extend from the surface of the corium and protrude into the epidermis. They are most numerous where the skin is most sensitive and in these areas they are arranged in parallel ridges, different in each individual, which are useful as fingerprints.

The basal layer of cells in contact with the corium contains the pigments, which give the skin its colour. The pigment protects the body from the harmful effects of the sun’s rays as dark colours absorb radiation. The scales of the surface prevent the entrance of bacteria into the tissues since they cannot digest these dried-up cells and make their way through them. Once the epidermis is broken by a cut or prick, infection may enter the tissues and sepsis may follow.

The nerve endings in the skin are for the most part sensory, and are of different varieties to give the various different sensations of which the skin is capable, namely, the sensations of touch, heat, cold and pain. The nerves of touch end in round bodies known as the touch or tactile corpuscles, which are stimulated by pressure, and the nerves of heat, cold and pain in delicate, tree-like branches. A few of the branches of these nerve endings pass into the epidermis. Heat is experienced only if a hot object touches the skin over the termination of a special nerve ending affected by heat. In some parts the nerve endings are so close together that this is not appreciated but where the nerve endings are less numerous, as over the back of the hand, it is possible to find spots where heat can be felt (hot spots) and others where cold is felt (cold spots).

The arteries supplying the skin form a network in the subcutaneous tissue and branches supply the sweat glands and the hair follicles. Fine capillaries also pass into the papillae.