Anatomy and Physiology of the Skin

Abstract

Human skin consists of a stratified, cellular epidermis and underlying dermis. Beneath the dermis is a layer of subcutaneous fat separated from the rest of the body by a vestigial layer of striated muscle. The outermost layer is the stratum corneum, where cells have lost the nuclei.

Other cells in the epidermis are melanocytes, Langerhans cells, and Merkel cells. Melanocytes are dendritic cells that distribute packages of melanin pigment to the surrounding keratinocytes to give skin its color.

The skin adnexa are composed of eccrine and apocrine glands, ducts, and pilosebaceous cells. They have various roles, but can all act as a replacement epidermis, in that reepithelialization occurs after damage to the surface epidermis.

Human hair growth is cyclic, but each follicle operates as an individual entity. Hair has protective as well as sociobehavioral importance.

Nails act to help grasp small objects and protect the fingertips against trauma and serve a sensory function.

The main components of the dermis are collagen, elastic fibers, and extracellular matrix. Collagen is the skin’s principal stress-resistant substance. Elastic fibers do little to resist deformation and skin tearing but do play a role in maintaining elasticity.

Subcutaneous tissue lies beneath the dermis, with lipocytes lobules separated by fibrous septa composed of collagen and large blood vessels; it serves as buoyancy, energy repository, and an endocrine organ.

Skin’s many functions include thermoregulation, immune response, and UV protection.