Anatomy of the Skin

The Integumentary System

• The skin and its accessory structures make up the integumentary system, which provides overall protection to the body.
• The skin is composed of multiple layers of cells and tissues held together by connective tissue.

Structure of the Skin

• The skin consists of two main layers: epidermis and dermis, and a closely associated layer: hypodermics.
• The epidermis is the most superficial layer, attached to the deeper dermis.
• Accessory structures, such as hair, glands, and nails, are found associated with the skin.

Layers of the Epidermis

Stratum Corneum

• The stratum corneum is the most superficial layer of the epidermis, exposed to the outside environment.
• This layer is composed of 15-30 layers of dead, keratinized cells that help prevent microbial penetration and dehydration of underlying tissues.
• Cells in this layer are shed periodically and replaced by cells from the stratum granulosum.

Stratum Lucidum

• The stratum lucidum is a smooth, translucent layer found only in thick skin of palms, soles, and digits.
• This layer is composed of dead, flattened keratinocytes packed with eleidin, a clear protein rich in lipids.
• Eleidin provides a barrier to water and gives the layer its transparent appearance.

Stratum Granulosum

• The stratum granulosum has a grainy appearance due to changes in keratinocytes as they are pushed from the stratum spinosum.
• Cells in this layer become flatter, their cell membranes thicken, and they generate large amounts of keratin and keratohyalin.
• These proteins make up the bulk of the keratinocyte mass in the stratum granulosum and give the layer its grainy appearance.

Stratum Spinosum

• The stratum spinosum is where keratin synthesis begins, and keratinocytes release a water-repelling glycolipid that helps prevent water loss from the body.