Courses on Cosmetology- PG Diploma/Fellowship/Masters. More Info WhatsApp -9604715783. SKIN ANATOMY As you must be knowing skin is the largest organ of the body. The surface area of skin is 1.7sq.m. and constitutes 16-20% of total body weight. Human skin is of two types: 1) Glabrous skin (non- hairy) e.g. Palms & amp; Soles 2) Non-Glabrous (hair-bearing). Skin is divided into 3 layers- 1) Epidermis 2) Dermis 3) Subcutaneous layer EPIDERMIS- The epidermis is the outermost layer of skin, which forms an outer protective covering of the body. Contains no blood vessels but has many small nerve endings. Consists of stratified epithelial cells. Varies in thickness on palms of hand and soles of feet, but thin and delicate on eyelids. The free surface of the epidermis is marked by linear furrows and ridges of variable size. It is arranged in five layers: 1) Stratum Corneum 2) Stratum Lucidum 3) Stratum Granulosum 4) Stratum Spinosum 5) Stratum Germinativum STRATUM CORNEUM OR CORNEAL CELL LAYER- It contains dead flattened cells. Cells are generated in the stratum germinativum and old cells from the surface of the stratum corneum. The function of the stratum corneum is to keep the skin waterproof and prevent the skin from cracking and bacterial infection. The continuous outward movement of epidermal cells constitutes a barrier for the agents which tend to penetrate the skin from outside. It takes 30 days for the cells to be reproduced in the stratum germinativum and move upwards to replace the cells on the skin surface. STRATUM LUCIDUM- It is thinner than the stratum corneum and is almost transparent This layer acts as a barrier controlling the its function is the transmission of water through the skin. STRATUM GRANULOSUM OR GRANULAR CELL LAYER This layer varies in thickness e.g. It is thickest in the palms of hands and soles of feet. These flattened cells have evidence of keratohyalin granules, which reflect light and give the skin a shiny look. STRATUM SPINOSUM OR CELL LAYER OR MALPIGIAN CELL LAYER- It contains a very fine filamentous structure called Tonofilaments, which consist of a long chain of amino acids. The cells in the layer have specialized cell wall structures called the Desmosomes, through which they are attached as well as to the cells of the basal cell layer. Tonofilaments are attached to the desmosome and form a Criss cross pattern in the cytoplasm of the cell and provide a sort of skeleton to the cells. Stratum Germinativum This is the deepest layer of the epidermis, which is in contact with the dermis below from which it gets nutrient fluid from the blood capillaries. This layer is regenerative. One in every 10 cells are melanocytes which produce melanin. Melanin the substance that gives color to the skin is a series of chemical reactions with the amino acid tyrosine. Mel anin protects the underlying layer of skin from the harmful effect of certain U.V. Rays. DERMIS. It is the innermost layer of skin also called the ‘True Skin’. It is tough, flexible, and highly elastic. It is thicker on the palms of hands and soles of feet but is exceedingly thin and delicate on eyelids. It consists of connective tissue with elastic and collagen fibers and numerous blood vessels, lymphatic vessels, and nerves. It also contains sebaceous glands, hair follicles, etc.The dermis is arranged in Two layers: 1. Papillary Layer; 2. Reticular Layer 1. Papillary Layer – It contains more elastic tissue than collagen fibers. but it contains projections of elastic tissue that point upward into the epidermis called the papillae, which contain blood capillaries (small blood vessels) and nerve endings and nourish the epidermis. Collagen is a protein-based fibrous substance, the skin elastin to create tone& amp; elasticity. 2. Reticular Layer It lies in between the papillary and the subcutaneous layer. it contains more collagen fibers and less elastic fibers. It contains the following structures, in the network. i. Fat cells ii. Blood vessels iii. Lymph vessel iv. Sebaceous Glands v. Sweat Glands vi. Hair Follicles vii. Arrector Pilli muscles 3. Subcutaneous Layer 1) Lies below the dermis 2) It is a thick layer of loose connective tissue and fatty tissue. This tissue is also called adipose tissue. 3) This fatty tissue varies in thickness according to the age, sex, and general health of an individual. 4) It gives smoothness and contour to the body. 5) It stores fat for use as energy. 6) It serves as an insulating layer. 7) It acts as a protective cushion for the outer skin. FUNCTION OF SKIN 1) Barrier function: a) Permeability Barrier b) Barrier of penetration of microorganisms and chemicals. c) Mechanical barrier d) Barrier to ultra violet radiation. 2) Regulation of body temperature. 3) Sensory functions. 4) Immunological function. 5) Vitamin D synthesis. 6) Social and sexual communication.