question_answer

    Describe the structure and function of different types of epithelial tissues Draw the diagram for each type of epithelial tissue.

Answer:

                  Epithelial tissues are of following types: (a) Simple squamous epithelium (b) Stratified squamous epithelium (c) Columnar epithelium (d) Cuboidal epithelium   (a) Simple squamous epithelium: They are present in cells lining blood vessels or lung alveoli where transportation of substances occurs through selectively permeable surface, there is a simple flat kind of epithelium. (b) Stratified squamous epithelium: Skin epithelial cells are arranged in many layers to prevent wear and tear. Since, they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium. (c) Columnar epithelium: Where absorption and secretion occur, as in the inner lining of the intestine, these tall epithelial cells are present. This columnar epithelial facilitates movement across the epithelial barrier. In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium. (d) Cuboidal epithelium: These form the lining of the kidney tubules and ducts of salivary glands where these provide mechanical support. Sometimes, a portion of the epithelial tissue folds inward and a multicellular gland is formed. This is glandular epithelium.        (a) Meristematic cells are continuously dividing cells so they have a prominent nucleus and dense cytoplasm. But since these cells do not store food material or waste materials, they lack vacuole. (b) Sclerenchyma cells have lignified cell walls which makes them compact and leaves no intercellular spaces. (c) Pear has sclerenchymatous stone cells which are granular in texture. Hence, we get the crunchy and granular feeling while chewing a pear. (d) The branches of a tree have collenchyma cells which provide tensile strength to plant parts. (e) The husk of a coconut tree is made up of sclerenchyma cells which have lignified cell walls. Lignin makes the cells compact and leaves no intercellular spaces.