Bioenergetic Profiling in the skin

Abstract

The skin is the largest organ of the human body, with an average surface area between 1.2and 2 m2. The skin thickness varies considerably over different parts of the body, andbetween men and women and the young and the old [1]. It is organized into threemain layers that consist of the outermost epidermis, the dermis, and the hypodermis(Fig. 12.1A). According to the ontogeny of the human skin, the epidermis is derivedfrom the ectoderm during embryogenesis. The initial single layer undergoes program-matic differentiation to reach a highly sophisticated stratified epithelium composedmainly of keratinocytes in different stages of differentiation [2,3]. By the time of birth,the fully formed epidermis can regenerate itself continually. Underlying the epidermisand separated by the basal membrane, we can find the dermis, which derives from themesoderm. The dermis is a connective tissue that provides mechanical structure due tothe presence of collagen and elastin fibers present in the extracellular matrix (ECM)around the fibroblasts. The dermis also contains the cutaneous appendages such as hairfollicles, sebaceous glands, sweat glands, sensory nerves, and lymphatic and blood vascu-lature. Finally, the hypodermis or subcutaneous tissue is composed mainly of adipose cellsuncharged of fat reservoir. All these components of the skin play critical functions such asphysical, chemical, and biologic barriers protecting against environmental and pathogenicinsults, thermoregulation, excretion, absorption, metabolic functions, and sensation.