Skin Structure & Function PDF

Structure and Functions of Skin Introduction: Skin is the largest organ of the human body. It is an impressive and vital organ. It is a fleshy surface with hair, nerves, glands and nails. It consists of hair follicles which anchor hair strands into the skin. It acts as a barrier between outside and...

Structure and Functions of Skin Introduction: Skin is the largest organ of the human body. It is an impressive and vital organ. It is a fleshy surface with hair, nerves, glands and nails. It consists of hair follicles which anchor hair strands into the skin. It acts as a barrier between outside and inside environment. The skin has different thicknesses and textures. E.g. the skin under the eyes is as thin as paper but is thick at the soles of the feet and palm. The skin acquires an area of 20 square feet on our body surface. It protects us from external elements, regulates the body temperature by releasing water in the form of sweat, and allows sensations such as touch, heat, and cold. It also guards the bones, muscles and other vital organs of our body. To know more about skin it is very important to explore the structure and function of the skin in detail. Structure of Skin It provides a protective covering throughout our body and acts as the body’s initial barrier against external harmful substances or foreign particles. The hair is made up of a protein called keratin, and the same protein is found in hooves, horns, claws and nails of other animals too. The structure of the skin is made up of three layers of, namely: Epidermis Dermis Hypodermis Epidermis It is the outermost layer of the skin. The cells in this layer are called keratinocytes. The keratinocytes are composed of a protein called keratin. Keratin strengthens the skin and makes it waterproof. Melanocytes that produce melanin are also present in this layer. In addition, Merkel cells essential for light-touch sensation and Langerhans cells, part of the immune system are also present on the skin. The epidermis is subdivided into the following layers: Stratum corneum Granular cell layer Spinous cell layer Basal cell layer Basal layer It is beneath all other layers of the epidermis, where new cells are produced continuously. As a result, cells get an upward thrust by the continuous formation of new cells. They grow actively because of the blood supply below this layer due to the presence of blood vessels. Spinous and Granular layer As these cells approach the next layer, they vary in their shapes and sizes. These irregularities give rise to the next layer, the spinous layer, above which the cells proceed to the granular layer. Cells hence begin to shrivel and die as a result of being far away from the blood supply. This results in the formation of a protein called Keratin. Stratum Corneum The outermost layer of the epidermis is the stratum corneum, which consists of dead and uniform scale-like cells which are overlapped. These cells contain abundant keratin and provide rigidity to the skin. These cells are regularly peeled off the skin’s surface which is balanced by the cells of the basal layer. Types of Epidermal Cells There are three main cell types in the epidermis: Melanocytes – These cells are located in the basal cell layer and produce a pigment called melanin which is absorbed by the new cells to protect against harmful sun rays. The two factors that govern the melanin quantity in one’s body is – genes and amount of exposure to sunlight. Keratinocytes – They are the main cells which are produced in the basal layer and approach towards the outermost layer. Langerhans – These cells are specialized to protect the body against foreign particles and hence is part of the immune system. The epidermis and the dermis layer are connected through a dermo-epidermal junction and contain the basement membrane. Dermis Beneath the epidermis is the dermis layer. It consists of papillae which form finger-like projections. This layer constitutes of fat, fibres and collagen which makes the skin flexible and strong. Dermis synthesizes Vitamin D to absorb calcium on exposure to sunlight. It consists of blood vessels which supply blood for the formation of new cells. They are also vital in regulating body temperature. Nerves in the dermis are sensitive to environmental factors such as pressure and temperature. Also, it contains the hair follicles and sebaceous oil gland which produces sebum. It acts as a lubricant and protects the skin by acting against the microbes. Sweat glands are produced all over the skin and release sweat through specialized ducts. They help the body to eliminate salts and minerals such as urea. An arrector pili muscle is attached to each hair follicle. This helps in the erection of hair when we experience cold or strong emotions. Hypodermis This subcutaneous layer is made up of fat and forms the innermost layer. Its thickness is dependent on the region where they appear and vary. For example, the area around the eye is comparatively thinner for the easy movement of the eye. Fat stored provides energy and is crucial in reacting to ambient temperature. It insulates the body from heat and cold. It cushions the internal organs, muscles and bones, and protects them from any injuries Function of Skin Following are a few important function of the skin in the human body: Protection from the Environment This is foremost and the most important function of the skin. It keeps the pathogens away so that they do not enter into the skin and cause any harm. Prevents Water Loss Humans possess thick skin that loses less water. In deserts, the human skin gets thicker to prevent water loss to dry air. Organisms with thin skin have the possibility of losing water all the time and need to stay near water to prevent it from drying. Sensation Skin is the main sense organ that can sense touch, heat, pressure, cold, pain, and pleasure. A network of nerves transmits these signals to the brain. Thus we can respond appropriately to a particular stimulus. Regulation of Temperature Our skin loses water through perspiration and cools itself, thereby, removing heat from the body. It also allows the hot blood to move to the surface of the skin, where its heat is radiated out of the skin. The phenomenon of “goosebumps” is also a temperature regulation response. Camouflage Many animals exhibit the phenomenon of camouflage where their skin produces colours and patterns that blend in with the surroundings and protects them from predators. Also, it makes it easier for predators to catch their prey by making themselves invisible in the surroundings. The skin of chameleons can release different amounts of pigments at their own will. Storage The skin can store fats and water in its tissues. These provide extra insulation to our body. The animals found in colder regions develop thick layers of fat to prevent themselves from the outside cold. Excreting Scent Signals The sweat secreted by our skin can also act as a signal to other organisms. Many animals mark their territories by secreting some scent from the glands in their skin which contains information about its age, health, gender, and availability to the mate.