Yfirhúðin

Yfirhúðin, also known as the epidermis, is the outermost layer of the skin in humans and many other animals. It serves as a protective barrier against the external environment, preventing water loss and the entry of pathogens. The epidermis is composed of several layers of cells, the most abundant of which are keratinocytes. These cells produce keratin, a tough protein that gives the epidermis its strength and resilience.

The epidermis is constantly shedding its outermost cells, a process called desquamation, and replacing them with new cells from the basal layer. This renewal process helps to maintain the integrity of the skin and remove any accumulated debris or microorganisms. The epidermis also contains melanocytes, cells that produce melanin, the pigment responsible for skin color and protection against ultraviolet radiation.

Different regions of the body have varying thicknesses of epidermis. For example, the epidermis on the soles of the feet and palms of the hands is significantly thicker than on the eyelids. This variation is related to the amount of friction and wear that these areas experience. The epidermis itself does not contain blood vessels; it receives nutrients and oxygen through diffusion from the dermis, the layer beneath it. This avascular nature contributes to its role as a barrier. The epidermis is essential for maintaining homeostasis and protecting the underlying tissues.