Skin for HST Part 1 PDF

Skin Human skin is the outer covering of the body, consisting of an outer layer, the epidermis, and an inner layer, the dermis (see illustration). The epidermis protects the body from injury and from invasion by parasites. It is the membrane or organ that covers the outer body of the human bein...

Skin Human skin is the outer covering of the body, consisting of an outer layer, the epidermis, and an inner layer, the dermis (see illustration). The epidermis protects the body from injury and from invasion by parasites. It is the membrane or organ that covers the outer body of the human being, and its main function is to protect the entire body through its physical properties, as it resists moisture and at the same time prevents the penetration of fluids into the various tissues of the human body. The skin also acts as an organ of excretion (by the secretion of sweat) and as a sense organ. It also helps to prevent the body from becoming dehydrated. The combination of erectile hairs, sweat glands, and blood capillaries in the skin form part of the temperature-regulating mechanism of the body. The skin has seven layers of dermal tissue and protects muscles, bones, ligaments, and internal organs. It may appear hairless. There are two general types of skin, hairy and hairless (hairless) skin. Because it interacts with the environment, the skin plays an important role in protecting the body from pathogens, and excessive water loss. Its other functions are insulation, temperature regulation, sensation, vitamin D production, and protection of the B vitamin folate. Severely damaged skin will attempt to heal by forming scar tissue. This often results in discoloration and loss of pigment. In humans, skin pigmentation varies across populations, and skin type can range from dry to oily. This skin type provides a rich and diverse habitat for bacteria, which contain approximately 1,000 species from 19 families, present on human skin. 1  Structure of the skin The skin has mesodermal cells , and pigmentation, such as melanin provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation in sunlight. It also contains DNA repair enzymes that help reverse UV damage, so that people who lack the genes for these enzymes have high rates of skin cancer. One form that is most often caused by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be fatal. Human skin pigmentation varies across populations in striking ways. This has led to people being classified based on skin color. The skin is the largest organ of the human body. For the average human, the surface area of skin is between 1.5–2.0 square meters. Skin thickness varies greatly throughout the body, and between men and women, young and old. An example is the skin on the forearm, which averages 1.3 mm in males and 1.26 mm in females. The average square inch (6.5 cm²) of skin contains 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and over 1,000 nerve endings. The average size of human skin cells is about 30 micrometres, but there are variables. Skin cells typically range from 25– 40 micrometres (µm) in size, depending on a variety of factors.The skin consists of three basic layers: the epidermis, dermis, and hypodermis. The skin ,epidermis, "epi" from the Greek meaning "above" or "above", is the outermost layer of the skin. It forms a waterproof, protective layer over the body's surface that also acts as a barrier to infection and is composed of stratified epithelial tissue with an underlying basal lamina.The epidermis contains no blood vessels, and the cells in the deeper layers are nourished almost exclusively by oxygen diffused from the surrounding air and to a much lesser extent by capillaries that extend to the outer layers of the dermis. The main cell types that make up the epidermis are Merkel cells , keratinocytes , with melanocytes and Langerhans cells also present. 2  The epidermis can be further divided into the following layers (beginning with the outer layer): corneum, lucidum (only in the palms of the hands and soles of the feet), granular, spinous, and basal. Cells are formed by mitosis in the basal layer. Daughter cells (see cell division) move to the upper layers and form and form cells as they die due to isolation from the blood supply. Cytoplasm is released and keratin protein is introduced. They eventually reach the cornea and are exfoliated (desquamated). This process is called "keratinization". This keratinized layer of skin is responsible for conserving water in the body and keeping out other harmful chemicals and pathogens, making the skin a natural barrier to infection. Skin elements The epidermis has no blood vessels and is nourished by diffusion from the dermis. The main types of cells that make up the epidermis are keratinocytes , melanocytes , Langerhans cells, and Merkel cells. The epidermis helps regulate body temperature. Skin layers for human The epidermis is divided into several layers as cells form through mitosis in the inner layers. They move up the layer changing shape and composition as they differentiate and fill with keratin. They eventually reach the top layer called the stratum corneum and peel or slough off. This process is called keratinization and occurs over a period of weeks. The outer layer of the epidermis consists of 25 to 30 layers of dead cells. The first layer of the skin is called the epidermis , followed by the dermis , which is 3 cm thick. The epidermis and dermis are separated by the stratum corneum and the lamina , and fatty pads extend under the dermis that act as an insulator. The outer skin cells, the epidermis , arise from the stratum corneum and the lamina. The shape of the keratinocytes is like sheets that grow from within the cells. The outer skin crust consists of cells without a nucleus. The thickness of the outer layer of human skin varies according to its location and the external stress it is exposed to. It is one thickness in the abdomen, while it is one hundred thicknesses in the soles of the feet. 3