The Basic Structure of Skin Consists - Term Paper Example

?The Skin Introduction The simplest definition of skin is that it is “the outermost tissue of the body and the largest organ in terms of both weight and surface area”, states Igarashi (2007, p.1). To be more specific, skin comprises about 8% of the total body weight, weighs around 8 pounds, and is found to be nearly16, 000 square centimeters or 2 square meters in area for an adult body. Skin is formed of an intricate system of layers of cells, nerves and glands which will be described in detail in the coming sections. Skin is a covering on our bodies that not only protects our internal organs but also makes us look presentable to the world. It acts like a protective, waterproof fleshy shield that protects body from extremes of climates, temperatures, and harmful radiations. Structure/Anatomy The basic structure of skin consists of three layers (see figure 1): 1. Epidermis This is the outermost layer of the skin and is composed of cells called keratinocytes. These cells are composed of a tough protein, keratin, which is also found in hair and nails. They form layers that grow in the outward direction in a course of five weeks to take the place of exterior dead cells when they flake off. The Langerhans cells present in the epidermis provide immunity to the body against infections. 2. Dermis Dermis is the layer that lies beneath the epidermis and provides strength and elasticity to the skin (National Geographic Society, 2011). It contains fibers of collagen and elastin, and blood vessels which serve to regulate the flow of blood to the skin in extreme weathers. This layer also contains hair follicles and glands along with a complicated arrangement of nerve fibers and receptors that tend to respond to touch and temperature, conveying the feeling of pain and uneasiness to the receptors in brain and acting accordingly. 3. Hypodermis Hypodermis or subcutis is the final layer of the skin that consists of a network of collagen and fat cells that help conserve the body heat and act as shock absorbers to the internal organs. This layer also acts as a fuel reserve due to its fat cells, in cases of low food supply. This layer is rich in adipose tissue excluding some parts of the body like scrotum and eyelids (Elden, 1971, p.51). Histology Epidermis It consists of keratinocytes, dendertic cells and Merkel’s cells. Keratinocytes are the largest in number and produce keratin. Dendertic cells are the melanocytes (which form melanin) and the Langerhans cells. Merkel’s cells are the receptors for touch stimulus. Keratinocytes Keratinocytes are assembled in five layers: 1. Stratum basale (basal cell layer). These are the mother cells of epidermis because they continue to divide. They form a layer composed of columnar cells consisting of basal nuclei. This layer of cells is present on the basement membrane. The cells are linked with each other and also with the overlying cells through desmosomes which are the inter-cellular bridges or linkages between cells. 2. Stratum spinosum (prickle cell layer). This layer is composed of multiple layers of nucleated polygonal cells that are linked to each other through desmosomes. 3. Stratum granulosum (granular cell layer). This layer consists of multiple layers of nucleated cells which are spindled in shape. These cells hold thick basophilic keratohyalin granules which further contain lipids. With the help of desmosomes, these lipids form a waterproof barrier in the skin which helps to stop fluid loss from the body. 4. Stratum licidum (clear layer). This layer consists of eleidin granules which are dead and non-nucleated. This layer is well observed in thick epidermis. It acts as an intermediary layer between the stratum granulosum and startum corneum. 5. Stratum corneum (horny layer). This layer is composed of cells which are non-nucleated and are called squames. They are present in linear sequence in the layer and contain keratin that comes from the eleidin granules of the stratum licidum. Dermis It is subdivided into papillary layer and reticular layer. Papillary layer is composed of loose connective tissue with fine collagan fibers (type II) and reticular and elastic fibers and contains the nerve endings- Meissner’s corpuscles. The reticular layer is composed of dense connective tissue with coarse collagen fibers (type I) and elastic fibers that contain pacinian corpuscles (Montagna & Parakkal, 1974, p.88-95). Physiology The skin performs many important functions other than protecting the internal organs from the outside world, some of which are listed below. Regulation of Body Temperature The blood vessels present in the epidermis help regulate the body temperature. For instance, when it is too hot outside, these blood vessels increase the flow of blood to the skin so that heat can escape; while, in cold weather, the blood flow is restricted. Sebaceous glands are responsible for heat regulation. Production of Sweat Sweat glands help evaporate sweat from the body to lower the temperature. In low temperatures, the production of sweat diminishes which results in conservation of heat within the body. Salts, excess of minerals, urea and pheromones are also excreted by way of sweat. Protection and Immunity The skin is the first line of defense against pathogens and toxins from the surroundings. It provides a barrier that protects the underlying tissues from physical abrasion, invasion of bacteria, dehydration and UV radiation. The Langerhans cells of the epidermis provide immunity against many infections. Response to Stimuli The skin contains abundant receptors and nerve endings that sense stimuli. It causes the body to react to heat, cold, pain and pressure. Storage and Synthesis Skin acts as a storage center for lipids and water which is helpful in cases of short food supply. It also helps in the synthesis of vitamin D and B through UV radiation. Conclusion To sum it up, skin is the outermost layer of human body that acts as a barrier between the outside world and the internal tissues and organs, thus protecting the latter from harmful interactions with the outside. It consists of three layers: epidermis, dermis and hypodermis. Epidermis consists of five layers of keratinocytes which are composed of cells that perform important functions. Dermis is formed of papillary and reticular layers. Hypodermis is the subcutaneous layer and contains fat. Skin performs many important functions like regulating body temperature, cooling the body through sweat, protecting the body from harmful radiations and extreme temperatures, providing immunity, responding to external stimuli through sensors, and acting as a storage and synthesis center. Figure 1: Structure of Skin References Elden, H. R. (1971). Biophysical properties of the skin. New York: Wiley-Interscience. Igarashi, T. (2007). The Appearance of Human Skin: A Survey. USA: Now Publishers Inc. Montagna, W., & Parakkal, P. F. (1974). The Structure and Function of Skin. New York: Academic Press. National Geographic Society. (2011). Skin. Retrieved November 7, 2011, from http://science.nationalgeographic.com/science/health-and-human-body/human-body/skin-article/ Read More