26 February 2013

Structural Characteristics, Function and Location of Epithelial Tissue

      Ø  Structural Characterisics : The cells of the epithelial tissue lie closely or side by side on a basement membrane. There is no matrix in this tissue. On the basis of cell size, location in the animal body and nature of work, this tissue is of three types, sch as;
      1.      Squamous Epithelial Tissue
      2.      Cuboidal Epithelial Tissue
      3.      Columnar Epithelial Tissue
      Ø  Squamous Epithelial Tissue: Cells of this tissue are flat like scales; rnucleus is large (Fig- 1)
      Ø  Example: Wall of the Bowman's capsule of Kindey.
      Ø  Function: Mainly filtration and covering. ~
      Ø  Cuboidal Epithelial Tissue: Cells of this tissue are cuboidal, as the length,
       breadth and height of the cells are nearly equal (Fig-2).
      Ø  Example: Collecting tubules of the kidney
      Ø  Function: Mainly absorption and covering.
      Ø  Columnar Epithelial    
Tissue : Cells of this tissue are narrow and elongated like a
column (Fig-3)
      Ø  Example: On the internal wall of intestine.
      Ø  Function: Mainly secretion, protection and absorption
There are three kinds of  Epithelial Tissue based on basement membrane cells:

      1.      Simple Epithelial Tissue
      2.      Stratified Epithelial Tissue
      3.      Pseudo stratified Epithelial Tissue
      Ø  Simple Epithelial Tissue: On basement membrane the cells are arranged in a single layer.
      Ø  Example: Bowman's capsule of ki4ney; renal tubules, intestinal wall (Fig- 1,2,3).
      Ø  Stratified Epithelial Tissue: Cells are arranged on the basement membrane in more than one layer (Fig-4).
      Ø  Example: Integument of vertebrate animals.
      Ø  Pseudo stratified Epithelial Tissue: .Cells, of this tissue are arranged in a single layer on basement membrane. The cells are not of the same height. So this tissue appears to be stratified tissue (Fig-5).
       Ø  Example: Trachea.
Besides the cells of epithelial tissue. are transformed variously for different
functions. As:
1. Ciliated Epithelial Tissue: Found in the wall of the respiratory tube of
2. Flagellated Epithelial Tissue: Found in the endoderm of Hydra.
3. Pseudopodia Epithelial Tissue: Found in pseudopodial cells in the endoderms of Hydra and in the intestine of vertebrate animals.
4. Glandular Epithelial Tissue: This is a kind of epithelial tissue transformed into gland in the stomach and intestine of vertebrate animals.
5. Germinal Epithelial Tissue: This, is a kind of transformed epithelial tissue. From this tissue sperms and ovum are formed.
      Ø  General Functions of Epithelial Tissue: