Skin Histology
The
epidermis or cuticle (scarf-skin) is non-vascular, and consist of stratified epithelium. It is accurately molded on the papillary layer f the derma. It forms a defensive covering to the surface of the true
skin, and limits the evaporation of watery vapor from its free surface. It varies in thickness in different parts. In some situations, as in the palms of the hands and soles of the feet, it is thick, hard and horny in texture. This may be partly due to the fact that these parts are exposed to intermittent pressure, but that this is not the only cause is proved by the fact that the conditions exist to a very considerable extent at birth. The more superficial layer of cells, called the horny layer (stratum corneum), may be separated by maceration from deeper layers, which are called the rate mucosum or atratum Malpighii, and which consist of several layer of differently shaped cells. The free surface of the epidermis is marked by a network of linear furrows of variable size, marking out the surface into number of spaces of polygonal or lozenge-shaped form. Some of this furrow are large, as opposite the textures of the joints, and correspond to the folds in the
dermis produced by their movements.
In other situations, as upon the back of the hand, they are exceedingly fine, and intersect one another at various angles; upon the palmar surface of the hand and fingers and upon the sole of the foot these lines are very distinct and are disposal in curves.
They depend upon the large size and peculiar arrangement of the papillae upon which the epidermis is placed. The deep surface of the epidermis is accurately molded upon the papillary layer of the dermis, each papilla being invested by its epidemic sheath; so that when this layer is removed by maceration, it presents on its under surface a number of pits or depressions corresponding to the elevations in the papillae, as well as the ridges left in the intervals between them. Fine tubular prolongations are continued from this layer into the ducts of the sudoriferous and sebaceous glands.
Skin Disorder by Infections
Acne, or acne vulgaris, the most common skin diseases, is a
skin condition thought to be secondary to hormonal changes of adolescence. Folliculitis, on the other hand, is caused by infection of hair follicles by staphylococci. The condition is sometimes called barber’s its, because individuals with beard tend to have deeper hair follicles that are more likely to be affected by bacteria. Furuncles (boils) and carbuncles are deeper and more serious infection of hair follicles, resulting in abscess formation.
Streptococcal pyoderma, or impetigo, and erysipelas are contagious infections caused by the entry of certain strains of streptococcal bacteria into breaks in the skin. Streptococcal pyoderma is characterized by the formation of localized crusty lesions. Erysipelatous lesions are usually widely spreading zones of redness, swelling, and blistering in the skin. Erysipelas is accompanied by systemic effects, including chills and fever; certain forms can rapidly involve large areas of the skin and can cause prostration and death.
Ringworm of the scalp (tinea cruris, or “jock itch”) are fungal infections of the skin. The term ringworm arises from the circular form of the lesions. Dermatophytosis of the foot, or “athlete’s foot,” is also caused by a fungus. Fungal infections are often accompanied by itching, burning, stringing, and seepage of tissue fluids at the site of infection.
Scabies and pediculosis are common parasitic infections.
Scabies is caused by mites that burrow into the skin upper the
epidermis layer. The mites excretion of waste products into the skin causes intense itching, especially at night. Adults often acquire scabies by sleeping with or having sexual relations with an infected person. Pediculosis is a louse infestation of the scalp, trunk, or pubic area (“crabs”). Each of the three kinds is caused by a different species of louse.
The most common viral infections of skin are herpes complex (cold sore or fever sore) and herpes zoster (shingles). Warts are another form of viral infection. Several types of warts occurs on different parts of the body, each one caused by a particular type of virus.
Related:
Skin disorder by Chemicals
