Yfirborðshúð

Yfirborðshúð, often translated as epidermis, refers to the outermost layer of skin in animals. It is a protective barrier that shields the underlying tissues from environmental damage, pathogens, and dehydration. The epidermis is constantly being renewed, with old cells shedding and new cells forming from the basal layer. This layer is avascular, meaning it lacks blood vessels, and receives nutrients and oxygen through diffusion from the dermis below.

The epidermis is composed of several distinct layers, each with specialized cells. The stratum basale, the deepest layer, contains actively dividing keratinocytes, the primary cells of the epidermis. As these cells mature and migrate upwards, they produce keratin, a tough protein that forms the protective outer layer. Other important cell types found in the epidermis include melanocytes, which produce melanin pigment responsible for skin color and UV protection, and Langerhans cells, which play a role in the immune response.

The thickness of the epidermis varies across the body, being thinnest on the eyelids and thickest on the palms of the hands and soles of the feet. This variation reflects the different levels of protection and wear these areas experience. The health and integrity of the epidermis are crucial for overall skin function and protection against a wide range of external threats. Damage to the epidermis can lead to increased susceptibility to infection and impaired barrier function.