Biology 121 Lab Supplement: Tissues - Epithelial Tissue

Introduction

• Focus on epithelial tissue in this lecture; other tissue types and connective tissue will be covered in separate videos.
• Study of tissues is known as histology.
• Tissues are a group of cells performing specific functions.

Biological Hierarchy

• Cell Level: Smallest structural unit capable of life.
• Tissue Level: Cells working together.
• Organ Level: Combination of tissues (e.g., heart is cardiac muscle and connective tissue).
• Organ System Level: Multiple organs working together (e.g., cardiovascular system).

Four Main Types of Tissues

1. Epithelial Tissue
   • Covers surfaces and lines cavities.
   • Forms glands (e.g., sweat glands).
2. Connective Tissue
   • Fills spaces, provides structural support, transports (e.g., blood), and stores energy (e.g., adipose tissue).
3. Muscle Tissue
   • Involved in movement, posture, and body temperature regulation.
4. Nervous Tissue
   • Conducts electrical impulses.

Epithelial Tissue

• Functions: Covers and lines internal and external surfaces, forms glands.
• Two Groups:
  • Covering and Lining Epithelium: Lines organs, cavities, and different tracts (e.g., respiratory tract).
  • Glandular Epithelium: Forms glands that secrete substances.

Characteristics of Epithelial Tissues

1. Cellularity: closely packed cells with minimal extracellular fluid.
2. Polarity: Different surfaces (apical surface - exposed, basal surface - attached to tissue).
3. Attachment: Cells attach to a basement membrane connected to connective tissue.
4. Avascularity: No blood vessels; nutrients diffuse from adjacent tissues.
5. Regeneration: High regenerative ability due to continuous replacement from stem cells.
6. Nerve Supply: Sensitive; good nerve supply (e.g., ability to read Braille).

Classification of Epithelial Tissues

• Based on Shape:
  • Squamous: Scale-like.
  • Cuboidal: Box-like.
  • Columnar: Column-like.
  • Transitional: Changes shape based on tension (e.g., urinary bladder).
• Based on Layers:
  • Simple: Single layer.
  • Pseudostratified: Appears multi-layered but is a single layer.
  • Stratified: More than one layer.

Functions Based on Layers

• Simple: Allows for diffusion, osmosis, secretion, and absorption.
• Stratified: Provides protection (e.g., skin).
• Transitional: Allows for distension and shape change (e.g., bladder).

Conclusion

• Focus on specific types of epithelial tissues in the next video.
• Understanding function and location is crucial for identification.