Lecture on Epithelial Tissue

Overview

• Comparison between epithelial and connective tissues
• Characteristics of epithelial tissue

Characteristics of Epithelial Tissue

• Tightly Packed Cells: Minimal extracellular material
• Free Surface: One side exposed, not attached
• Basement Membrane: Two layers
  • Basal Surface: Attached to basal lamina via hemi-desmosomes
  • Connective Tissue: Always found beneath epithelial tissue
• Avascular: No blood vessels penetrating the basement membrane
  • Nutrients obtained through diffusion from connective tissue
• Innervated: Rich nerve supply
• Proliferative: Capable of rapid mitosis

Classification of Epithelial Tissue

• Layers
  • Simple: One layer of cells attached to basement membrane
  • Stratified: Two or more layers
  • Pseudostratified: Appears layered but is actually one layer
• Cell Shapes
  • Squamous: Flat, thin; appear amorphic from top view
  • Cuboidal: Cube-like, round nucleus
  • Columnar: Column-like, oval nucleus towards the bottom

Special Features of Columnar Tissue

• Cilia: Hair-like structures for movement (e.g., mucus, eggs)
• Microvilli: Short projections for nutrient absorption
• Goblet Cells: Mucus-producing glands

Functions and Locations

• Simple Epithelia: Ideal for diffusion, osmosis, filtration, absorption
• Stratified Epithelia: Primarily for protection

Naming of Epithelial Tissue

• Based on layers and cell shape (e.g., simple cuboidal, ciliated simple columnar)
• Naming helps infer function and location

Specific Types of Epithelial Tissue

Simple Squamous Epithelium

• Function: Diffusion, osmosis, filtration
• Types:
  • Mesothelium: Lines outside of organs; part of serous membranes
  • Endothelium: Lines inside of structures (e.g., blood vessels, heart)
• Appearance: Thin, like "fried eggs" from top view

Simple Cuboidal Epithelium

• Function: Absorption, filtration
• Locations: Urinary tubules, surface of ovaries

Simple Columnar Epithelium

• Types:
  • Ciliated: With cilia for movement
  • Non-ciliated: With microvilli for absorption
  • Goblet Cells: Present in both types for mucus production
• Location: Often found in GI tract

Summary

• Epithelial tissue serves various functions including lining, covering, and gland formation
• Different types of epithelial tissues are distinguished by their structure and location
• Understanding the structure aids in predicting the function and activities of the tissue