Basic science dermatology

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The skin is split up into two main layer: Epidermis

Dermis

Epidermis

This can be considered for its different cell types, or its separate layers.

Cell types:

Keratinocytes: over 95% of cells. So-called because they are responsible for producing keratins.

Melanocytes: these are responsible for producing the pigment melanin and are present on the basal layer.

Langerhans cells: These are dendritic cells involved in immune response.

Merkel cells: Neuroendocrine cells associated with nerve endings in the epidermis.

Layers:

Basal Layer: one-cell thick layer which lays on top of the basement membrane. Here, basal cells (keratinocytes), are undergoing mitosis. Developing keratinocytes travel up into the stratum spinosum.

Spindle Layer/Stratum Spinosum: Consists of keratinocytes which are tightly joined together by intercellular desmosomes. These lead to the resultant "prickle-cell" description.

Granular Layer/Stratum granulosum: Consists of granules (made from keratohyalin - filaggrin and keratin), and Odland bodies (Keratinosomes) which are responsible for the secretion of lipid intercellularly,

Stratum Corneum (Horny): Flattened keratinocytes, which are dead. These are called corneocytes. These produce involucrin, which requires skin-specific transglutaminase.

Keratinocytes are therefore differentiating, before dying to from corneocytes in the stratum corneum. These cells are then shed individually (make up dust). However, if something goes wrong with this terminal differentiation process, then individual corneocytes may not be shed, and instead clumps of corneocytes may gather to form a visible SCALE.

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