Epithelial Tissue and Membranes

Overview

• Epithelial tissue forms sheets lining surfaces and covering organs within body cavities.
• The basal surface of epithelial tissue always binds to connective tissue.
• This combination forms an epithelial membrane.
• The connection occurs at the basement membrane, which is a meshwork of proteins and substances.

Basement Membrane Structure

• Composed of two layers:
  • Basal lamina: produced by epithelial cells.
  • Reticular lamina: produced by connective tissue cells.
• Functions:
  • Adheres epithelial tissue to connective tissue.
  • Semi-permeable, allowing diffusion of substances.

Types of Epithelial Membranes

1. Mucous Membranes (Mucosa)

   • Line passageways opening to the external environment (e.g., digestive, respiratory tracts).
   • Some epithelial cells produce mucus for moisture and protection.

2. Serous Membranes (Serosa)

   • Line body cavities not open to the external environment (e.g., thoracic, abdominal pelvic cavities).
   • Double-layered: Parietal layer (lines cavity wall) and Visceral layer (covers organs).
   • Secrete serous fluid to reduce friction.
   • Specific serous membranes include:
     • Pleura: associated with lungs.
     • Pericardium: associated with the heart.
     • Peritoneum: associated with the abdominal cavity.

3. Cutaneous Membrane (Skin)

   • Covers and protects the entire body surface.
   • Consists of the epidermis (epithelial) and dermis (connective tissue).

Epithelial Tissue Types

• Different structures affect function.

Layers

• Simple Epithelium: One layer of cells.
• Stratified Epithelium: More than one layer of cells.
• Pseudostratified Epithelium: Appears multi-layered but all cells contact the basement membrane.

Cell Shapes

• Squamous: Flat cells.
• Cuboidal: Cube-shaped, as tall as wide.
• Columnar: Taller than wide.

Modifications

• Microvilli: Increase surface area for absorption.
• Cilia: Move substances across cell surfaces.

Specific Epithelial Types

• Simple Squamous Epithelium: One layer of flat cells.
• Simple Cuboidal Epithelium: One layer of cube-shaped cells.
• Simple Columnar Epithelium: One layer of column-like cells, may have microvilli or cilia.
• Stratified Squamous Epithelium: Multiple layers, superficial cells are flat.
  • Keratinized: Dry type.
  • Non-keratinized: Moist type.
• Stratified Cuboidal/Columnar Epithelium: Multiple layers, superficial cells are cuboidal/columnar.
• Pseudostratified Ciliated Columnar Epithelium: Appears stratified, with cilia.
• Transitional Epithelium: Found in urinary system, stratified but not named as such.

Study Tips

• Focus on structure-function relationship.
• Learn to identify different types under a microscope.
• Practice writing specific epithelial tissue names accurately.