BIOLOGY CH18 Organization of Tissues — Science STD 9 — Question

Simple Epithelium :
1. It is formed of a single layer of cells. It forms a lining for the body cavities and ducts.
2. Simple epithelium is further divided into the following types.

• Squamous epithelium
• Cuboidal epithelium
• Columnar epithelium
• Ciliated epithelium
• Glandular epithelium

(i) Squamous epithelium :

• It is made up of thin, flat cells with prominent nuclei. These cells have irregular boundaries and bind with neighbouring cells.
• The squamous epithelium is also known as pavement membrane, which forms the delicate lining of the buccal cavity, alveoli of lungs, proximal tubule of kidneys, blood vessels etc.
• It protects the body from mechanical injury, drying and invasion of germs.
• 
• (ii) Cuboidal epithelium:
  • It is composed of single layer of cubical cells.
  • The nucleus is round and lies in the centre.
  • This tissue is present in the thyroid vesicles, salivary glands, sweat glands, exocrine pancreas.
  • It is also found in the intestine and tubular part of the nephron (kidney tubules) as microvilli that increase the absorptive surface area.
  • Their main function is secretion and absorption.
  (iii) Columnar epithelium:
  • It is composed of a single layer of slender, elongated and pillar like cells.
  • Their nuclei are located at the base.
  • It is found lining the stomach, gall bladder, bile duct, small intestine, colon, oviducts and forms a mucous membrane. ‘
  • They are mainly involved in secretion and absorption.
  • 
  • (iv) Ciliated epithelium :
    • Certain columnar cells bear numerous delicate hair like out growths called ilia and are called ciliated epithelium.
    • Their function is to move particles or mucus in a specific direction over the epithelium.
    • It is seen in the trachea of wind-pipe, bronchioles of respiratory tract, kidney tubules and fallopian tubes of oviducts.
    • (v) Glandular epithelium :
    • Epithelial cells are often modified to form specialized gland cells which secrete chemical substances at the epithelial surface.
    • This lines the gastric glands, pancreatic tubules and intestinal glands.
    •