Types of Epithelial Tissue
Epithelial tissue is a fundamental type of tissue in the body, serving various functions such as protection, absorption, secretion, and sensation. It is classified based on the shape of cells and the number of layers.

1. Classification by Cell Layers
- Simple Epithelium: A single layer of cells that facilitates absorption, secretion, and filtration. It is found in areas where diffusion occurs, such as the alveoli of lungs and capillaries.
- Stratified Epithelium: Multiple layers of cells providing protection against abrasion and wear. Commonly found in the skin, mouth, and esophagus.

2. Classification by Cell Shape
- Squamous Epithelium: Composed of flat, scale-like cells. It is ideal for diffusion and filtration, found in the lining of blood vessels and the alveoli of lungs.
- Cuboidal Epithelium: Made of cube-shaped cells, primarily involved in secretion and absorption. It is found in glands and the kidney tubules.
- Columnar Epithelium: Features tall, column-like cells that often have microvilli or cilia. It aids in absorption and secretion, typically found in the digestive tract and respiratory system.

3. Specialized Types
- Pseudostratified Epithelium: Appears to have multiple layers due to cell height variations but is actually a single layer. Found in the respiratory tract, it often contains cilia for movement of mucus.
- Transitional Epithelium: Specialized to stretch and is found in the bladder. Its unique structure allows it to accommodate fluctuating volumes of urine.
Understanding these types of epithelial tissue is crucial for studying how various organs function and maintain homeostasis in the body.