ABSTRACT
Skin, the largest organ in the human body, is composed of two main layers, the dermis and the epidermis (Figure 26.1). The dermal layer consists primarily of extracellular matrix (ECM) proteins, with a sparse population of broblasts, providing structural support. In contrast, the epidermis is almost entirely cellular and imparts an immunological barrier function. In addition to these two main cell types, a variety of other cells reside within the skin, creating hair follicles, blood vessels, sweat, and sebaceous glands, and generating pigment and nervous function (Figure 26.1). The human integument regulates heat and hydration status; senses external stimuli such as heat, pressure, and touch; and provides a barrier against pathogens and damage from the external environment. As a result, signi cant skin damage or disease poses a major health risk.
