Four Types of Tissues

The human body, like most other animals, comprises four primary tissue types:
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
A tissue is defined as a group of similar cells organized to perform a specific function. Sponges are an exception and lack true tissue structures.

Epithelial tissue is characterized by:
- Densely packed cells directly connected to each other.
- Cell junctions link neighboring epithelial cells.
- Forms sheets of cells that are one to many layers thick.
Function: Lines the surfaces of the body, both outer and inner.
- Examples:
  - Outer layers of skin.
  - Inner lining of digestive and respiratory systems.
  - Lining of many internal organs and blood vessels.