Epithelial Tissue Overview

Epithelial Tissue

• Epithelial tissue covers body surfaces, lines body cavities and forms glands.
• Key characteristics include:
  • Cells closely packed with minimal extracellular matrix
  • Specialized cell junctions, like tight junctions, adhering junctions, and gap junctions.
  • Supported by connective tissue
  • Avascular (lacks blood vessels), relying on diffusion for nutrients
  • High regenerative capacity.
• Classification based on shape and layers:
  • Shape: Squamous (flat), cuboidal (cube-shaped), columnar (column-shaped).
  • Layers: Simple (single layer) or stratified (multiple layers).
• Functions: Protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.
• Examples:
  • Simple squamous epithelium in the alveoli of the lungs for gas exchange.
  • Stratified squamous epithelium in the skin providing protection.
  • Cuboidal epithelium in the kidney tubules for selective reabsorption.
  • Columnar epithelium in the intestines for absorption and secretion.
  • Glandular epithelium (specialized for secretion) found in various organs.

Connective Tissue

• Connective tissue supports, connects, and separates different tissues and organs.

• Core components include:

  • Cells dispersed in an extracellular matrix, composed of ground substance and fibers.
  • Ground substance: fluid, gel-like, or solid matrix, varying in consistency.
  • Fibers: collagen, elastic, and reticular fibers providing structural support and elasticity.

• Classification:

• Connective tissue proper: Loose connective tissue (areolar, adipose, reticular) and dense connective tissue (regular, irregular, elastic).

• Specialized connective tissues: Cartilage (hyaline, elastic, fibrocartilage), bone, and blood.

• Functions:

  • Binding and support: Connecting tissues, providing framework for organs.
  • Protection: Cushioning organs, forming barriers.
  • Insulation: Adipose tissue.
  • Transportation: Blood, which transports substances throughout the body.

• Examples:

  • Areolar tissue: Supporting many organs.
  • Adipose tissue: Energy storage, insulation.
  • Dense regular connective tissue: Tendons and ligaments.
  • Cartilage: Supporting structures (ears, nose, joints).
  • Bone: Supporting and protecting the body.
  • Blood: Transporting oxygen, nutrients, and wastes.

Key Differences between Epithelial and Connective Tissues

• Cell packing: Epithelial tissues have tightly packed cells, while connective tissues have cells scattered within an extracellular matrix.
• Vascularity: Epithelial tissues are avascular, relying on diffusion for nutrients, while connective tissues are generally vascular, except for cartilage.
• Matrix: Epithelial tissues have little to no extracellular matrix, whereas connective tissues are defined by their extracellular matrix, which varies greatly depending on the tissue type and function.
• Functions: Epithelial tissue functions primarily in covering and lining, whereas connective tissue's roles are diverse, including support, connection, and protection.