Anatomy and Physiology of the Skin

The skin is the outermost and largest organ making up almost a fifth of the weight of the human body. Important functions of the skin are protection, thermoregulation and reception, and mediation of mechanical, nociceptive and potentially chemical stimuli. The skin consists of an outer five-layered epidermis and an inner two-layered dermis. The peculiarity of the different sub-layers highly depends on the respective body site. The epidermis is a constantly self-renewing tissue with cells migrating from the deep basal cell layer towards the superficial corneal layer. The epidermis and dermis are connected via the highly organized epidermal–dermal junction that can be considered an independent anatomical unit. The dermis contains the vast majority of the collagens of the skin, which makes it the key layer for the biomechanical characteristics of the skin. The collagens are affected by intrinsic and extrinsic ageing processes with morphological and biomechanical implications on the tissue. Most of the body is covered by hairy skin. Hairless skin exists on the palms of the hand and the plantae of the foot. Underneath the skin lies a thick layer of fat that connects the skin to deeper collagen-rich structures such as fasciae, aponeuroses or the periosteum.