Capiton: High-power micrograph of epidermis.This micrograph displays epidermis from a dark-skinned patient. Note the prominent basilar keratinocyte pigmentation. The increased skin pigmentation results from a greater accumulation of melanin packages in the keratinocytes of the stratum spinosum, not an increased number of melanocytes in the stratum basale. (Courtesy D. Cassarino, MD, Ph.D.)
The integument is the anatomical name for skin. As the body’s largest organ, it covers the entire body and is continuous with the mucous membranes of the oral and anal cavities. The integument consists of 2 main components: The epidermis, an ectoderm-derived layer of stratified squamous keratinized epithelium, and the dermis, an underlying mesoderm-derived layer of connective tissue. Closely associated with the skin are accessory structures known as skin appendages, which develop as epidermal downgrowths into the dermis. These include sweat glands, sebaceous glands, hair, and nails. Beneath the integument, the subcutaneous layer (superficial fascia,hypodermis) consists of loose connective tissue characterized primarily by adipose cells. Substantial collagen bundles anchor the dermis to the hypodermis in a way that permits most areas of the skin to move freely over the deeper tissue layers.
Skin is classified as thick or thin according to the caliber of the most superficial stratum of the epidermis (stratum corneum) as well as the presence or absence of certain epidermal derivatives such as glands and hair.
- Thick skin. Thick skin covers areas that are subject to the most abrasion. It is present on the plantar surface of the feet and toes and on the palmar surface of the hands and fingers.
- Epidermal ridges. Thick skin demonstrates distinct patterns of epidermal ridges that form whorled, friction ridges. These epidermal ridges mimic the underlying dermal papillae to form prominent grooves and raised crests in the surface of the epidermis. These friction ridges are unique to individuals and generate exclusive finger and toe prints (dermatoglyphic patterns).
- Thin skin. Present on all other areas of the body. Thin skin is characterized by a relatively thin surface layer of keratin, a lack of friction ridges, and, often, the presence of hair follicles. Thin skin is not adapted for much “wear and tear.”