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Biology Structural Organization Animals D131 ((Types of Animal tissue:…

- - - - What are Epithelial tissues?
        
        ''Epi'' means above
        
        ''Thelial'' means grow
        
        They are protective tissues and generally above all of the other tissues
        
        Covering of external surfaces, organs & cavities in the body
        
        Not only it can cover the external surfaces, but also act as a cover for the internal organs
        
        So the main purpose of the Epithelial tissues if to provide protection
        
        They act as boundaries, keeping different body systems, separate
        
        They are made up of closely packed cells forming a continuous sheet
        
        So why are they closely packed?
        
        If they are not closely packed, and there is a leakage between the Epithelial tissue that means the boundary will be leaking
        
        If there is a leakage between the boundary, harmful and toxic fluids or material can go inside the organs and damage the organs
        
        No blood vessels are within these tissues so they are non vascular tissues
        
        How do we know that they are no blood vessels?
        
        for example you look at your hand and if you press it a little harder, does blood come out?
        
        No, because the uppermost layer is made out of the Epithelial tissue. But if you stab it with a knife, your hand will be bleeding because it went through the Epithelial layer and it is hurting some other tissues where blood vessels are present and that is why is starts bleeding
        
        Why - they don't have the blood vessels?
        
        Blood vessels have blood flow and the purpose of the blood is to transfer the nutrients to different parts of the body but the Epithelial does not have a blood vessel
        
        So how do they get their nutrients? They get the nutrients through diffusion, by diffusion through their walls, they can exchange nutrients and water so they do not need blood vessels
      - Structure of the Epithelial tissues
        
        There is no or very, very less intercellular spaces
        
        Because if you look at an Epithelial tissue you will notice that there are not much space between them, so just below the Epithelial tissue, you have the connective tissues that separates the Epithelial tissue
        
        So if something goes through your body, and it passes the basement membrane, your hand starts to bleed because there is a blood vessel located under the basement membrane
        
        One surface is free; other is basal surface (attached to basement membrane)
        
        The extracellular fibrous basement membrane separates the Epithelium from underlying tissue
        
        The basement membrane, whose job is to separate the Epithelial tissue from the connective tissue which is located below it
      - Where do we find the Epithelial tissues?
        
        Lining of mouth
        
        Inside of our mouth there is a very thin lining for the protection of the oral cavity so that lining you will see the Epithelial tissue
        
        Skin
        
        The entire body skin in covered by the Epithelial tissue for protection
        
        Lung alveoli
        
        Inside the lung you have the alveoli which actually helps in absorbing oxygen so you have Epithelial tissue
        
        Lining of blood vessels
        
        So even on the lining of the blood vessels have Epithelial tissue
        
        Kidney tubules
      - Epithelial tissues: Functions
        
        Protects the underlying tissues & organs
        
        Their main purpose is protection and they act like a boundry
        
        Regulates exchange of materials between the body & external environment and also between different parts of the body
        
        it acts as a boundary and whichever is needed is allowed and which is not needed is not allowed to go in
        
        absorbs food and nutrients
        
        So absorption is another important function of the Epithelial tissue
        
        Secretes chemicals like
        
        Enzymes
        
        etc
        
        Saliva
        
        Hormones
        
        So these are also important functions of the Epithelial tissues