epidermis
The epidermis is the outermost layer of the skin and is composed of epithelial cells
The epidermis is the outermost layer of the skin and is composed of epithelial cells. It is responsible for protecting the underlying tissues, regulating water loss, and acting as a barrier against pathogens and harmful UV radiation from the sun.
The epidermis is made up of five layers, namely the stratum corneum, stratum lucidum (only present in thick skin), stratum granulosum, stratum spinosum, and stratum basale.
1. Stratum corneum: This is the outermost layer of the epidermis and consists of dead skin cells known as corneocytes. These cells are filled with keratin, a tough protein that provides structural strength to the skin. The stratum corneum acts as a protective shield against mechanical and environmental damage.
2. Stratum lucidum: This layer is only present in areas of thick skin, such as the palms and soles of the feet. It consists of translucent cells that lack a nucleus and are packed with keratin filaments.
3. Stratum granulosum: In this layer, the keratinocytes begin to produce an important protein called keratohyalin, which helps to form the keratin fibers. Additionally, lipid-filled granules accumulate in the cells of this layer, contributing to the water repellency of the skin.
4. Stratum spinosum: This layer contains several layers of cells that appear spiny due to the desmosomes holding them together. These desmosomes provide mechanical strength and help resist friction and shearing forces on the skin’s surface.
5. Stratum basale: Also known as the basal layer, this is the deepest layer of the epidermis where new cells are constantly produced. It contains stem cells that continuously divide and differentiate into keratinocytes. These keratinocytes gradually migrate toward the surface, replacing the older cells that are sloughed off.
The epidermis itself does not contain blood vessels, but it is nourished by diffusion of oxygen and nutrients from blood vessels in the underlying dermis. It also contains specialized cells called melanocytes, which produce the pigment melanin responsible for skin color and protection against UV radiation.
Overall, the epidermis plays a vital role in protecting and maintaining the health of the skin.
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