- As you must be knowing skin is the largest organ of the body. The surface area of skin is 1.7 sq.m. and constitutes 16-20% of total body weight .
Human skin is of two types :1) Glabrous skin (non- hairy ) e.g. Palms & Soles 2) Non Glabrous (hair bearing )
Skin is divided into 3 layers- 1) Epidermis 2) Dermis 3) Subcutaneous layer
EPIDERMIS=Epidermis is outer most 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
STRTUM CORNEUM OR CORNEAL CELL LAYER-It contains dead flattened cells. Cells are generated in the stratum germinativum and old cells from the surface of stratum corneum . The function of stratum corneum is to keep the skin water proof and prevent the skin cracking and becoming open to 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 stratum corneum and is almost transparent This layer acts as a barrier controlling the it function is transmission of water through the skin.
STRATUM GRANULOSUM OR GRANULAR CELL LAYER -This layer is varies in the thickness e.g. It is thickest in the palms of hands and soles of feet . These flattened cells have evidence of kerotophyaline granules .which reflects light and give the skin shiny look.
STRATUM SPINOSUM OR CELL LAYER OR MALPIGIAN CELL LAYER-It contains very fine filamentous structure called Tonofilaments, which consist of long chain of amino acids. The cells in the layer have specialized cell wall structure called the Desmosomes, through which they are attached to each other as well as to the cells of basal cell layer. Tonofilaments are attached to 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 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 very 10 cells are melanocyte which produce melanin. Melanin the substance that gives colour to the skin is series of chemical reaction with the amino acid tyrosine. Melanin protects the underling layer of skin from harmful effect of certain U.V. Rays. It is the innermost layer of skin also called the True Skin .
it is tough , flexible and highly elastic.it is thicker on palms of hands and soles of feet but is exceedingly thin and delicate on eyelids. It consists of connective tissue with elastic and collagen filbers and numerous blood vessels, lymphatic vessels and nerves. It also contains sebaceous glands, hair follicles etc
.Dermis is arranged in 2 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 epidermis called the papillae , which contain blood capillaries (small blood vessels) and nerve endings and nourish the epidermis. Collagen a protein based fibrous substance , the skin elastin to create tone& elasticity.
2.Reticular Layer It lies in between the papillary and the subcutaneous layer . it contains more collagen fibers and less elastic fibres. It contains following structures , in the network .i. Fat cellsii. Blood vessel Lymph vessel. Sebaceous Glands. Sweat Glands vi. Hair Follicle. Arector 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 individual.4)It gives smoothness and contour to the body.5) It stores fat for use of 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 micro organisms and chemicals. c) Mechanical barrier 2) Regulation of body temperature. 3) Sensory functions. 4) Immunological function.5) Vitamin D synthesis.6) Social and sexual communication.