Dermatology Overview

The Skin

The skin is the largest organ in the body. Averaging about 1 to 2 mm in thickness with the thickest skin on the palms and soles and the thinnest on the eyelids and scrotum. The skin is the envelope that wraps our body, keeps all the pieces together and serves numerous functions. It may be light or dark, smooth or wrinkled, but it helps define how we appear to others. This body covering, the skin is composed of the epidermis, dermis and the hypodermis.

The Epidermis

The epidermis (0.075 to 0.15 mm thick) is composed mostly of compact, avascular stratified squamous epithelial cells. There are actually five layers to the epidermis (from the innermost to the exterior); the stratum germinativum, stratum spinosum, stratum granulosum, stratum corneum and the stratum lucidum. The lowest layer, the basal cell layer (stratum germinativum) is where new cells (keratinocytes) divide and move upward. The keratinocytes change from living cells to dead, thick-walled, flat, non-nucleated cells containing keratin as they move towards the skin surface.

Dermis

The dermis (about 1 to 4 mm thick), or basement membrane separates the epidermis from the lower fatty layers and actually physically supports the epidermis. The dermis is composed mainly of collagen and elastin embedded in a mucopolysaccharide substance, containing fibroblasts and mast cells. The dermis also contains a network of nerves, lymphatic and blood vessels, supplying hair follicles, sebaceous glands and sweat glands. It is this layer where the cutaneous sensations occur, for example, itching from the upper region, stinging from the middle region and pain in the region closest to the subcutaneous fat.

Hypodermis

The subcutaneous tissue, called the hypodermis is composed of loose connective tissue and adipose tissue. This layer aids in thermal control, holds nutrients and provides cushioning and/or padding. Burns extending into this area require close monitoring of the patient, depending upon the extent of involvement.

PURPOSE OF THE SKIN

The skin, the largest organ in the body, is the protective barrier between the body and the environment. The skin works to protect the body from chemicals and pathogenic organisms; its functions are dependent upon, and in association with, age, immunologic status, underlying disease states, use of oral/topical medications and the preservation of an intact stratum corneum.

In addition to protection. the skin also serves for temperature control, pigment development, water regulation/moisture loss and even vitamin synthesis.

The skin can be challenged by wounds, burns, chafing. drying. internal physiological disorders. chemicals and bacteria. resulting in alterations and may involve the different skin layers.