Epithelial Tissue (Epithelium):

Epithelial tissue is a type of tissue that forms coverings or linings for body surfaces, cavities, ducts, and tubes. It has a free surface that faces body fluids or the external environment.

Cells are tightly packed with minimal intercellular matrix (extracellular material between cells)

Types of Epithelial Tissue:

Simple Epithelium:

• Composed of a single layer of cells.
• Functions as a lining for body cavities, tubes, and ducts.
• Further classified based on cell shape: squamous, cuboidal, and columnar.

Compound Epithelium:

• Consists of two or more layers of cells.
• Provides protection, particularly in the skin.

Types of Simple Epithelium:

Squamous Epithelium:

• Cells are flat and scale-like.
• Found in locations where diffusion or filtration is important, such as in the lining of blood -vessels (endothelium) and air sacs of the lungs (alveoli).

Cuboidal Epithelium:

• Cells are cube-shaped with equal dimensions.
• Often found in areas involved in secretion and absorption, such as kidney tubules and glandular ducts.

Columnar Epithelium:

• Cells are taller than they are wide, resembling columns.
• Functions in absorption, secretion, and sometimes movement (e.g., cilia).
• Examples include the lining of the digestive tract and the respiratory tract.

Ciliated Epithelium:

• Some columnar or cuboidal epithelial cells have cilia on their free surface.
• Cilia are hair-like structures that can move rhythmically, creating directional movement of particles or mucus over the epithelial surface.
• This type of epithelium is found in areas like the bronchioles and fallopian tubes.

Glandular Epithelium:

• Certain columnar or cuboidal cells become specialized for secretion.
• Glandular epithelium is of two main types: unicellular and multicellular glands.
• Unicellular glands consist of individual glandular cells, like goblet cells in the digestive tract.
• Multicellular glands are clusters of cells, like salivary glands.
• They secrete various substances like mucus, saliva, enzymes, and hormones.

Compound Epithelium:

This type of epithelium is made up of multiple layers of cells. It is primarily involved in providing protection against mechanical and chemical stresses. It can be found in areas like the skin, buccal cavity, and lining of various ducts