Browse the corpus

Our skin serves many functions - including protective, sensory, temperature regulation, and fluid homeostasis. The outermost layer, the epidermis, is primarily involved in protective functions both as a physical and an immunologic barrier. These functions can all be correlated histologically, and derangements of these functions have clinical ramifications. This article will cover the structure and function of the normal epidermis. It will also briefly describe tissue preparation, immunohistochemistry, light microscopy, and electron microscopy. Lastly, it will describe some pathologies and select clinical and histologic correlations.

Many inflammatory pathologic conditions are associated with disruptions in the local skin microbiota leading to pathology or changes in the skin itself, leading to altered relations with the local microbiota. Teenage acne vulgaris involves clogging pores secondary to sebaceous hyperplasia and lipid release into the follicular lumen, which is exacerbated by Cutibacterium acnes activation of keratinocytes.[18] Other skin conditions that are genetic or innate in nature represent aberrations in the normal structure and function of the skin. For example, psoriasis is a chronic papulosquamous genetic skin disorder characterized by hyperproliferation in the epidermis stimulated by immune dysfunction. Certain T-cell immune cytokines, most notably IL-17 and IL-23, are upregulated. This leads to keratinocyte proliferation, neutrophil chemotaxis, and angiogenesis.[19] Another prominent genetic condition that affects the epidermis is atopic dermatitis. This condition is driven by a mutation in Filaggrin, an element of the epidermis. This deficiency allows for increased colonization and penetration by the skin microbiome, which promotes inflammation and drives the characteristic pruritus.[20]