The skin is the covering layer of the body. It has a protection function as is seen from the type of epithelium that its epidermis layer has. It has a stratified sqaumous keratinized epithelium, which is composed of several layers of cells.
The skin of humans is composed of two layers. These are the epidermis and the dermis layers. The epidermis is the outer layer of the skin and it contains several types of cells that have different functions.
The dermis layer is the inner layer of the skin and it contains blood vessels and nerves and lymphatic cells. The epidermis does not contain blood vessels but contains nerve endings for touch and heat receptors.
The first type of cells that I discuss here is the keratinocytes. They are available in the epidermis and produce the protein keratin. This protein functions by protecting the skin from several hazardous material such as chemicals and microbes.
In certain fungal infections of the skin, the fungi produce an enzyme that is called keratinase. This enzyme has a harmful effect on the skin cells causing digestion of the keratin layer in the skin.
The other cell type that is located in the epidermis is the melanocytes. They are responsible for the production of the pigment melanin. Melanin contributes to the brown color of the skin.
People with dark skin color have high concentration of the pigment melanin in their skin. Other pigments that are available in the skin and which impart color to it are bilirubun and carotene.
Bilirubin is produced in red blood cells from the metabolism of the molecule hemoglobin. It can form also under pathological conditions such as in hemolysis or red bood cells and in the case of gallbladder blockage by a cholesterol stone.
The epidermis contains also cells of immunologic origin. They are called langerhans cells. These cells originate in the red bone marrow and after their synthesis they migrate to the skin and become functional there.
They fight microbes invasion of the skin surface but are UV light sensitive. THey fight also any antigen that can be present in the skin.
Cells of the nervous system are also located in the epidermis. They are called Merkel cells. They have a function that is related to the sensation of touch. They have free nerve endings in the skin which can detect or sense touching of the skin.
A skin disorder that invloves keratinocytes which is called psoriasis is characterized by fast division of keratinocytes and their fast migration from their basal layer to the epidermis. They form a thick layer of keratin in the skin surface.
The skin of humans has several important functions. They include the synthesis of vitamin D. Vitamin D is essential for the absorption of calcium in the intestine as well as for its metabolism in the body. Therefore its availability in the diet in the form of tablets is important.
Two organs in the body synthesize vatamin D from precursor molecules. These are the kidneys and the skin. The skin utilizes UV radiation from the sun to sythesize vitamin D.
Therefore, adequate exposure of the skin to sun light is important in people deficient with vitamin D. Women after menopause often suffer from osteoporosis due to lack of the hormone estrogen which also helps in the metabolism of calcium as vitamin D.
The skin also has a function related to regulating body temperature through the process of sweating. The evaporation of sweat from the skin surface helps in lowering the body temperature.
Another function to the skin and which is considered as a non specific resistence is as a barrier against pathogens and microbes. This is so due to the multilayered cells in the epidermis and which are called stratified squamous epithelium.
Skin cancer can arise due to either exposure to carcinogenic compounds such as benzene and acridine or due to exposure to ionizing radiation from the sun such as UV light.
Skin cancer can be of several types. These are basal cell carcinoma and squamous cell carcinoma and melanoma. Basal cell carcinoma has its origin in the basal layer of the epidermis. It does not have a tendency to metastasize.
Squamous cell carcinoma originate in the squamous cells of the epidermis. Its tendency to metastasize is variable. Melanoma has its origin in the skin cells of melanocytes.