Skin

From ArticleWorld

The skin is the outer layer of tissue that surrounds the exterior of humans and all higher animals. I carries multiple functions, including being the primary barrier against pathogens, being the major organ of sensation and aiding in the synthesis of vitamins B and D.

Anatomy

The skin consists of two major layers, the epidermis and the dermis. Beneath these skin layers is the hypodermis which is technically not part of the skin. The epidermis is the outer skin layer and contains cells known as “stratified epithelium” that covers the basement membrane. This layer of cells has no circulation of its own but is fed via nourishment provided by the dermis.

The epidermis contains melanocytes which define the pigment of the skin, Keratinocytes which produce keratin, the protective portion of the skin and provides a moisture barrier and Langerhans cells. Beneath the epidermis are the blood capillaries that nourish the layers and are connected to a larger arteriole and venule.

The dermis is the part of the skin that contains the larger blood vessels, nerves, hair follicles, sebaceous glands, and some smooth muscle. When the smooth muscle contracts around the hair papillae, goose bumps appear. This cell layer contains the connective tissue that supports the skin. This includes collagen, elastin and reticular fibers.

Fibroblasts that make new tissue, adipocytes that store fat and macrophages are present in this layer as well. Macrophages destroy any pathogens that get through the outer layers of skin or in the case of an injury. Sebaceous glands form the oily substance of the skin and sweat glands make sweat.

Skin functions

The skin provides a barrier between our bodies and the outside environment. The melanocytes in the skin protect our bodies from the sun’s UV radiation. They provide both a barrier to pathogens and the cells, such as macrophages and Langerhans cells, which are important in our immunity. The skin has multiple nerve endings that are very sensitive to the sensations of touch, heat, cold, vibration and pain.

Sweat glands in the skin help regulate our body temperature. These glands also excrete small amounts of uric acid, similar to that found in urine. The skin is also a storage center for fat and water. UV light acts on the skin and is part of how we make vitamin D and vitamin B. In addition the skin absorbs small amounts of oxygen and is the site of absorption of several types of medicines which are delivered through the skin via a patch or semi-solid vehicle.