Microanatomy of the skin

Introduction

The skin is one of the largest organs in the body, having a surface area of 1.8 m ² and making up about 16% of body weight. It has many functions, the most important of which is as a barrier to protect the body from noxious external factors and to keep the internal systems intact.

Skin is composed of three layers: the epidermis, the dermis and the subcutis ( Fig. 1.1 ), and supports a complex population of microflora on the surface (skin microbiome) (p. 10).

Epidermis

The epidermis is a stratified squamous epithelium that is about 0.1 mm thick, although the thickness is greater (0.8–1.4 mm) on the palms and soles. Its prime function is to act as a protective barrier. The main cells of the epidermis are keratinocytes , which produce the protein keratin. Keratinocytes are squamous cells functionally similar to all other structural epithelial cells as found in the airways and gastrointestinal tract. Keratinocytes differentiate upwards through the epidermis and their maturation states (p. 6) are divided into four stages (layers) ( Fig. 1.2 ).