Classify and describe epithelial tissue on the basis of structural modifications of cells.

(N/A) Epithelial tissue is classified into two main types based on the number of cell layers:
$1$. Simple Epithelium: Composed of a single layer of cells,functioning as a lining for body cavities,ducts,and tubes.
- Squamous Epithelium: Made of a single thin layer of flattened cells with irregular boundaries. Found in the walls of blood vessels and air sacs of lungs. Function: Diffusion boundary.
- Cuboidal Epithelium: Composed of a single layer of cube-like cells. Found in ducts of glands and tubular parts of nephrons in kidneys. Function: Secretion and absorption.
- Columnar Epithelium: Composed of a single layer of tall and slender cells. Nuclei are located at the base. Found in the lining of the stomach and intestine. Function: Secretion and absorption.
- Ciliated Epithelium: If 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. Function: To move particles or mucus in a specific direction.
- Glandular Epithelium: Some columnar or cuboidal cells get specialized for secretion. They are unicellular (e.g.,goblet cells) or multicellular (e.g.,salivary gland).
$2$. Compound Epithelium: Made of more than one layer (multi-layered) of cells and thus has a limited role in secretion and absorption. Their main function is to provide protection against chemical and mechanical stresses. 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.