Basics of Epithelial Tissues

Epithelial Tissue Basics

• Epithelia are classified by cell layers and shape: first name denotes cell layers, second denotes cell shape.

Types of Epithelia

• Simple epithelia: Composed of a single layer of cells.
• Stratified epithelia: Composed of multiple layers of cells.

Cell Shapes

• Squamous cells: Flat in shape, facilitating diffusion.
• Cuboidal cells: Cube-shaped, primarily involved in secretion and absorption.
• Columnar cells: Taller than wide, involved in secretion and absorption processes.

Specific Epithelial Types

• Simple Squamous:

  • Thin, flat cells in a single layer.
  • Functions: diffusion, filtration, some secretion.
  • Locations: lining of blood vessels, heart, lymphatic vessels.

• Simple Cuboidal:

  • Single layer of cube-shaped cells.
  • Functions: active transport, secretion, and diffusion.
  • Locations: kidney tubules, glands, and ducts.

• Simple Columnar:

  • Single layer of tall, narrow cells.
  • Functions: movement of particles (e.g., in bronchioles).
  • Locations: glands and some ducts.

• Stratified Squamous:

  • Multiple layers; basal cells are cuboidal or columnar, flattening at the surface.
  • Functions: protection against abrasion, infection barrier.
  • Location: outer layer of skin.

• Stratified Columnar:

  • Multiple layers with only surface cells being columnar; deeper cells are cuboidal.

• Pseudostratified Columnar:

  • Appears stratified but consists of a single layer where not all cells reach the apical surface.
  • Functions: typically involved in secretion and movement of mucus.

• Transitional:

  • Stratified tissue that appears cuboidal when unstretched and squamous when stretched.
  • Location: lining of the urinary bladder.

Cell Layer Classifications

• Simple: One layer of cells.
• Stratified: More than one layer of cells.

Cell Shape Classifications

• Squamous: Wider than tall (plate-like).
• Cuboidal: Equal height and width (cube-like).
• Columnar: Taller than wide (column-like).
• Transitional: Unique ability to change shape.
• Pseudostratified: Appears layered but is a single layer with varying cell heights.