Class 12 Biology Class 11 Biology Class 10 Science Class 9 Science NEET Entrance PDF & Web Notes PPT Slides Exam Special Online Tests All-in-One

Structural Organisation in Animals - Notes | Class 11 | Animal Tissues | Epithelial Tissues

A group of cells having the same origin, structure, and function are called tissues.

Animal tissues are classified into the following types:

  • Epithelial
  • Connective
  • Muscular
  • Neural

I. Epithelial Tissue (Epithelium)

  • It has a free surface that faces body fluid or the outside environment.
  • Covers or lines the body or body parts.
  • Compactly packed cells with little intercellular matrix.
  • Epithelial tissues are 2 types: Simple and Compound.

A. Simple Epithelium

  • It is composed of a single layer of cells. It lines body cavities, ducts and tubes.
  • Based on structural modification of cells, simple epithelium is 3 types:

    • Squamous Epithelium

  • Thin layer of flattened cells with irregular boundaries.
  • Found in the walls of blood vessels and lung alveoli.
  • Functions: Form a diffusion boundary.

    • Cuboidal (cubical) Epithelium

  • Composed of cube-like cells.
  • Found in ducts of glands and tubular parts of nephrons.
  • Functions: Secretion and absorption.
  • The epithelium of proximal convoluted tubule (PCT) of nephron in the kidney has microvilli.

    • Columnar Epithelium

    • Composed of tall and slender cells.
    • Their nuclei are located at the base.
    • Free surface may have microvilli.
    • Found in the lining of the stomach and intestine.
    • Functions: Secretion and absorption.
    Modifications of Columnar or Cuboidal Cells:
    • Ciliated Epithelium:
      • Cells bearing cilia on their free surface.
      • Present in the inner surface of hollow organs like bronchioles and fallopian tubes.
      • Functions: To move particles or mucus in a specific direction over the epithelium.
    • Glandular Epithelium: For secretion. They are of two types:
      • Unicellular: Consists of isolated glandular cells. E.g., Goblet cells of the alimentary canal.
      • Multicellular: Contains a cluster of cells. E.g., salivary glands.
    • Based on the mode of secretion, glands 2 types:
      • Exocrine Glands: Secretions are released through ducts (tubes). They secrete mucus, saliva, earwax, oil, milk, digestive enzymes, etc.
      • Endocrine Glands: Ductless. They produce hormones.
    Glandular Epithelium Diagram

    B. Compound Epithelium

    • Made up of more than one layer (multi-layered) of cells.
    • Limited role in secretion and absorption.
    • They cover the dry surface of the skin, the moist surface of the buccal cavity, pharynx, inner lining of ducts of salivary glands, and pancreatic ducts.
    • Function: Protect against chemical and mechanical stresses.
    Compound Epithelium Diagram

    Cell Junctions

    • The junctions that provide structural and functional links between adjacent cells.
    • Found in epithelium and other tissues.
    • They are three types:
      • Tight Junctions: Help to stop substances from leaking across a tissue.
      • Adhering Junctions: Perform cementing to keep neighboring cells together.
      • Gap Junctions: Facilitate communication between adjoining cells by connecting the cytoplasm for rapid transfer of ions, small molecules, and sometimes big molecules.

    Select a Topic 👇

    1. Animal Tissues (Epithelial Tissues) 2. Animal Tissues (Connective Tissues) 3. Animal Tissues (Muscle and Neural Tissues) 4. Cockroach- Morphology 5. Cockroach- Anatomy 6. Earthworm- Morphology 7. Earthworm- Anatomy 8. Frog- Morphology & Anatomy
    Download PDF
    Post a Comment (0)