Class 11 Biology Structural Organisation In Animals Epithelial tissues

Epithelial tissues

  • This tissue which has a free surface faces either a body fluid or the outside environment and thus provides a covering or a lining for some part of the body is called epithelial tissues.
  • The cells are compactly packed with little intercellular matrix.
  • There are two types of epithelial tissues
  • simple epithelium
  • compound epithelium.
  • Simple epithelium is composed of a single layer of cells and functions as a lining for body cavities, ducts etc.
  • Compound epithelium consists of two or more cell layers and has protective function as it does in our skin.

Simple epithelium

  • On the basis of structural modification of the cells, simple epithelium is further divided into three types
  • Squamous
  • Cuboidal
  • Columnar
  • The squamous epithelium is made of a single thin layer of flattened cells with irregular boundaries, found in the walls of blood vessels and air sacs of lungs.

Class_11_Biology_Structural_Organization_Squamous_Epithelium

Fig. Squamous epithelium

  • The cuboidal epithelium is composed of a single layer of cube-like cells, found in ducts of glands and tubular parts of nephrons in kidneys.

Class_11_Biology_Structural_Organization_Cubodial_Epithelium

Fig. Cuboidal epithelium

  • The columnar epithelium is composed of a single layer of tall and slender cells with nuclei located at the base and microvilli at the free surface, found in the lining of stomach and intestine.
  • If the columnar or cuboidal cells bear cilia on their free surface they are called ciliated epithelium, found in the inner surface of hollow organs like bronchioles and fallopian tubes.

Class_11_Biology_Structural_Organization_Ciliated_Epithelium

Fig. Ciliated columnar epithelium

  • Some of the columnar or cuboidal cells get specialized for secretion and are called glandular epithelium.
  • They are mainly of two types of glandular epithelium
  • Unicellular- consisting of isolated glandular cells. Example- goblet cells of the alimentary canal.
  • Multicellular- consisting of cluster of cells. Example- salivary gland.
  • On the basis of the mode of pouring their secretions, glands are divided into two categories-
  • Exocrine- secrete mucus, saliva, earwax, oil etc. which are released through ducts.
  • Endocrine glands- secrete hormones directly into the fluid bathing the gland, as they do not have ducts.

Class_11_Biology_Structural_Organization_Glandular_Epithelium

Fig. Glandular epithelium

Compound epithelium

  • Compound epithelium is made of more than one layer of cells.
  • Provide protection against chemical and mechanical stresses.
  • They cover the dry surface of the skin, the moist surface of buccal cavity, pharynx etc.

Class_11_Biology_Structural_Organization_Compound_Epithelium

Fig. Compound epithelium

Cell junctions

  • Cell junctions are the specialized junctions that provide both structural and functional links between its individual cells.
  • Three types of cell junctions
  • Tight junction
  • Adhering junction
  • Gap junction
  • Tight junctions help to stop substances from leaking across a tissue.
  • Adhering junctions perform cementing to keep neighboring cells together.

Gap junctions facilitate the cells to communicate with each other by connecting the cytoplasm of adjoining cells, for rapid transfer of ions, small molecules

Class_11_Biology_Structural_Organization_Cell_Junction

Fig. Cell junction

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