What is the epidermis?

The epidermis is avascular which means it contains no blood vessels or lymphatic. Consequently, nourishment is provided through the vessels of the underlying dermis, making the epidermis entirely dependent on the underlying dermis for nutrient delivery and waste disposal via diffusion through the dermo-epidermal junction. There are further layers within the epidermis which include; the stratum germinativum, stratum spinosum, stratum granulosum, and stratum corneum. The cells found residing within these layers have distinct roles and functions for maintaining tissue health. For example, ‘melanocytes’ found in and not limited to the basal layer of the epidermis are primarily responsible at producing a pigment, ‘melanin,’ which absorbs radiant energy from the sun and protects the skin from the harmful effects of ultraviolet radiation. Another key function of cells found within the epidermis is, ‘Langerhans cells.’ These originate from the bone marrow and are found in the basal, spinous, and granular layers of the epidermis. They serve as antigen-presenting cells, and one of their primary functions is ingesting foreign antigens, processing them into small peptide fragments and binding them with major histocompatibility complexes, subsequently presenting them to lymphocytes for activation of the immune system. To put it simply, they are key in the support and function of the immune system and fight off any toxins or foreign substances that may be present in the skin.