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skin - Coggle Diagram

- - - - Excretion
        
        Synthesis of Vitamin D
        
        Storage of food
        
        Grip
        
        Regulation of temperature
        
        the skin prevents loss of heat in cold weather and facilitates loss of heat in hot weather
        
        the skin stores reserve food in the form of a layer of fat contained in special cells
        
        The skin can synthesise vitamin D when exposed to sunshine.
        
        the skin assists in the process of excretion of water, salts and to a very limited extent, urea.
      - our skin serves as a sense organ for touch, pain, pressure, heat, etc.
    - - i) it protects the underlying tissue from mechanical **damage**
        
        ii) it holds the body fluids inside and prevents excess loss of water by evaporation
        
        iii) it prevents harmful substances or disease casing germs from entering the body.
        
        iv) it protects the body against excess ultraviolet light which is potentially very harmful
- - - - The dermis is the inner thicker layer of connective tissue made of elastic fibres. It is tough and flexible .
        
        At certain places, the dermis of our skin becomes thick such as the palms and soles , and very thing at other places such as the eyelids.
        
        The dermis contains several other structures- blood vessels, never fibres, sensory organs, hair follicles , sweat glands, etc.
        
        The outer region of the dermis which lies next to the Epidermis is raised into numerous small processes called papillae which contain blood capillaries and never endings.
        
        The nerve endings and sense organs here are concerned with the sensation of touch and pain.
    - - It is the outer thinner part of the skin.
        
        It is formed of stratified epithelium piled up layer after layer.
        
        At places, the epidermis becomes hard and thick as on the palms, soles and specially on the heels.
        
        It is devoid of blood vessels at all places.
        
        the epidermis has three sublayers :
        
        middle granular layer
        
        The granular layer is a very thin middle layer consisting of two or three sub-layers of flattened cells. Gradually, it gives way to the outermost cornified layer.
        
        inner malpighian layer
        
        The malpighian layer ( stratum malphigi ) is also called germinative layer and it is the innermost region of the epidermis.
        
        Its cells can actively divide to produce new cells which press and shift outward to replace the worn-out cells of the outermost cornified layer.
        
        Coloration of the skin is due to a pigment called melanin contained in the cells of the malpighian layer.
        
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        outermost cornified layer
        
        The cornified layer stratum corneum is the outermost layer consisting of several piled up layers of flattened dead cells.
        
        These cells are made of a fibrous structural protein called keratin
        
        The cornified layers is tough and offers protection from three things-
        i) mechanical damage.
        ii) bacterial infection
        iii) loss of water by evaporation
    - - Nails
        
        Nails are hardened keratinous plate like structure which grow as dead cells from the nail root , which lies below is skin at the base.
        
        When an open pore in the skin gets clogged due to dead skin cells or sebum from sebaceous glands , it black upon oxidation from air. Hence it is called a black head.
        
        a nail has three parts:
        
        bed
        
        it lies below the nail plate
        
        matrix
        
        it lies just below the skin, at the base of the nail. it is usually visible as whiteish half-moon at the base of the nail, it produces new cells which on maturation push out the older cells towards the tip of the nail, and cause growth of the nail.
        
        plate
        
        it is the outer hard part of the nail. it is made up of dead, keratinized cells
      - Mammary glands
      - Hair
        
        i) Hair shaft is the part that is projecting from the skin and may extend below the surface of the epidermis. In normal situation, they lie obliquely on the surface. ii) Hair root is the part which is embedded inside the dermis. The lowest part of the hair root is expanded to form a iii) Hair bulb which contains a projection of the dermis called hair papilla , with capillary blood supply.
        
        the hair follicle is a structure enclosing the hair root. It is composed of an epithelial and connective tissue sheath. The hair bulb and hair follicle together are responsible for the growth and elongation of the hair. The growth of the hair occurs from the addition of cells at the base, which soon die.
        
        hair in human beings is continuously lost and regrown. The duration is scalp hair is 2-5 years and that of eyebrows and eyelashes of 3-5 months.
        
        rest GK- from tb pg no 130.
      - Sweat glands
      - Sebaceous glands
        
        these branched glands usually open into a hair follicle , though sometimes they open directly to the outside.
        
        they give out an oily secretion called sebum which makes the hair and surface of the skin oily and waterproof to keep the epidermis supple and prevent loss of moisture due to evaporation.
        
        in cold and dry weather, the skin may become rough and leave a powdery surface when scratched; this is due to reduction of oil secretion from the sebaceous gland.
        
        in hot and humid weather, the skin becomes extra oily , this is due to increased secretion of sebum.
        
        Three common problems related to sebaceous glands :
        
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