Скачать с ютуб Anatomy & Physiology (47) = Integumentary System | Epidermis & Dermis | Layers of Epidermis & Dermis в хорошем качестве

Anatomy & Physiology (47) = Integumentary System | Epidermis & Dermis | Layers of Epidermis & Dermis

Download "Solution Pharmacy" Mobile App to Get All Uploaded Notes, Model Question Papers, Answer Papers, Online Test and other GPAT Materials - https://play.google.com/store/apps/de... The skin itself has two major tissue layers⎯the epidermis and the dermis. The epidermis is the outermost layer of skin, comprised of several sublayers. This layer of skin contains many cells, each called a keratinocyte, a keratin-producing cell found in the skin. Keratin is the structural protein that lends durability and water impermeability to skin, hair, and nails. Keratin also makes up the body's hair and nails. Cells that contain keratin are generated in the lower layers of the epidermis. These migrate upward, where they are progressively flattened. The topmost layer of the epidermis is composed of dead cells, filled with keratin. The dermis is the layer of the skin that sits directly beneath the epidermis. It is primarily composed of connective tissue that supports and strengthens the skin. It also contains sweat glands, sebaceous glands, nerves, blood vessels, hair follicles, and sensory receptors. The dermis is composed of two layers⎯the papillary layer and the reticular layer. The papillary dermal layer lies directly under the stratum basale of the epidermis. The papillary layer contains a network of small blood and lymph vessels that provide nutrients to the epidermis. These blood vessels also play a key role in thermoregulation. They dilate to release heat and constrict to conserve it. Epidermis part – Important points The outermost or epidermal layer of skin is composed of stratified squamous keratinized epithelial cells. The epidermal layer varies in thickness in different parts of the body. It is thickest where it receives the most abrasion and weight. For example – on the palm of hands and soles of feet, whereas it is much thinner over the ventral surface of the trunk. It does not have blood vessels or nerves, it receives nutrients from the capillaries of the dermis. The epidermis is made up of the following 05 layers – (01) Stratum corneum (Horny layer) (02) Stratum lucidum (Clear layer) (03) Stratum granulosum (Granular layer) (04) Stratum spinosum (Spiny layer) (05) Stratum germinativum or stratum basale (Regenerative layer) = The cells in the lowest layer divide by mitosis and the new cells formed push the older cells upwards towards the surface. Thus the old cells at the surface are continuously replaced by new cells. (01) Stratum Corneum - It is the outermost layer that consists of 25 to 30 layer of dead keratinized cells that are nonnucleated and are filled with keratin (Protein) which is responsible for its structural strength. The keratinized cells are also covered with lipids, which makes this layer an effective barrier, abrasion resistant and protect the deeper layer from injury and microbial invasion. These cells are constantly shed and replaced by cells from Stratum germinativum or stratum basale (Regenerative layer) (02) Stratum Lucidum – It lies directly beneath the stratum corneum and consist of 03 to 05 layers of flattened, transparent, dead keratinized cells. These cells exhibit a shiny character, hence this layer is name lucid (03) Stratum Granulosum – It is a thin layer that consists of 02 to 05 layers of flattened keratinocytes (Cell containing keratin). The cytoplasm of these cells contains keratohyalin granules, which convert tonofilaments (Keratin intermediates filaments that make up tonofibrils in the epithelial tissue) into keratin and lamellar granules (Specialized secretory granules of the keratinizing stratified squamous epithelia) which release a lipid-rich, water repellant secretions. (04) Stratum Spinosum – It lies above the stratum germinativum and consists of 08 to 10 layers of spiny keratinocytes. These cells have spine (Thorn) like projections, which connect one cell yo another and provide both strength and flexibility to the skin. (05) Stratum Germinativum - It is the deepest and most important layer of the skin because It is responsible for the formation of other upper epidermal layers. It consists of a single row of cuboidal or columnar keratinocytes, out of which some are stem cells that have the ability to divide by mitosis and thus continuously produce new cells known as “Keratinocytes” Get in touch with the solution by just clicking the following links- Facebook Group-   / solutionpharamcy   Mobile App - https://play.google.com/store/apps/de... New Channel (Pharmacy Dictionary)    / @pharmacydictionary   E-Mail for official and other work - [email protected] #solutionpharmacy #Pharmacologyclass #Pharmacognosyvideos #GPAT