In this week’s newsletter, we will remind ourselves about the different layers of the skin. This is a topic that many of us were taught as part of our training, but which may no longer be quite at our fingertips (so to speak). Still, it is an important subject that underlies everything we do in our everyday work and is well worth another look.
The skin is connective tissue that consists of cells, fibers, and an extracellular matrix. The epidermis is the thin outer layer of skin. The dermis is the thicker, inner layer of skin. Beneath the dermis lies a layer of loose connective tissue, called subcutaneous tissue, or the hypodermis. Deeper tissues; including muscle, tendon, ligament, joint capsule, and bone, lie beneath the subcutaneous tissue layer. The dermal-epidermal junction, or basement membrane zone, separates the epidermis from the dermis.
The epidermis is the tough, leathery, outer surface of the skin, ranging in thickness from .06 to 6mm, with the thickest portions located in the palms of the hands and the soles of the feet. The epidermis is arranged in 5 layers that represent different stages of cellular differentiation. As new cells are formed, older cells elongate and their membranes thicken as they are pushed upward into the next epidermal layer.
The deepest layer, the stratum basale or basal layer, is attached to the dermis below by a thin, acellular basement membrane. The basement membrane acts as scaffolding for the epidermis, and as a selective filter for substances moving between the epidermis and the dermis. The epidermis is avascular, receiving its blood supply through the diffusion of nutrients from the dermis across the semipermeable basement membrane.
The stratum spinosum is the next layer. It consists of several rows of more mature keratinocytes, which appear spiny under a microscope.
Just above the stratum spinosum is the stratum granulosum. This layer contains 3 to 5 flattened cell rows with increasing concentrations of keratin. As keratinocytes are pushed farther up and away from their dermal blood supply, they slowly die.
The stratum lucidum is a thin, clear layer of dead skin cells in the epidermis, and is named for its translucent appearance under a microscope. The stratum lucidum is found beneath the stratum corneum in areas where skin is thicker, such as the palms of the hands, and the soles of the feet.
The outermost layer of the epidermis is called the stratum corneum, or horny layer. This later consists entirely of dead keratinocytes. The stratum corneum can be 20 to 30 cells thick. The keratin in these cells helps keep the skin hydrated by preventing water evaporation. These cells can also absorb water, further aiding in hydration. This explains why you experience wrinkling of your skin when your fingers are immersed in water for long periods.
A good understanding of the anatomy and physiology of the skin is essential in order to manage wounds effectively. To learn more about the structure of the skin and about all areas of wound management, you may wish to consider becoming certified in wound care.
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