Lecture on Epithelial Tissue

Introduction

• Epithelial tissue is one of the four types of tissue in the human body.
• Found everywhere from the heart's interior to the skin.
• Importance in microscopic anatomy and influence on visible anatomy.
• The lecture will cover the histology of different types of epithelial cells.

Role and Function

• Epithelial tissue doesn't account for much body mass but is crucial in various body functions.
• Two main jobs:
  1. Forms layers of cells covering internal and external surfaces (e.g., lining of blood vessels, skin).
  2. Secretes substances within or outside the body.
• Forms the functional bulk of some organs (parenchyma), e.g., liver (~80% epithelial cells).

Characteristics

• Epithelial cells are polar with distinct top (apical) and bottom (basal) poles.
  • Basal pole: Contacts the basement membrane.
  • Apical pole: Faces the lumen or inside of a tube.
  • Can have special structures like cilia (e.g., in lungs).
• Below the basement membrane is the lamina propria, a layer of connective tissue with blood vessels.
• Lateral faces: Allow communication between neighboring cells via:
  • Gap junctions
  • Tight junctions
  • Desmosomes
• Epithelial tissue is avascular; gets oxygen/nutrients by diffusion from lamina propria.

Types of Epithelial Cells

• Cell Shapes:
  • Squamous (flat)
  • Cuboidal (cube-shaped)
  • Columnar (column-shaped)
• Organization:
  • Simple epithelium: Single layer.
    • Simple squamous: Lines blood vessels for easy substance passage.
    • Simple cuboidal: Found in places like seminiferous tubules for secretion.
    • Simple columnar: Found in GI tract for secretion/absorption.
  • Pseudostratified epithelium: Appears layered but is a single layer with different cell heights.
  • Stratified epithelium: Two or more layers, with types such as:
    • Stratified squamous
    • Stratified cuboidal
    • Stratified columnar
  • Keratinized epithelium: Stratified epithelium with dead, keratin-filled cells (e.g., skin).
  • Transitional epithelium: Stacks of different types allowing stretching (e.g., bladder).

Glandular Epithelium

• Types:
  • Exocrine glands: Release substances outside the body or into body cavities.
    • Examples: Goblet cells (GI tract), salivary glands, apocrine glands.
  • Endocrine glands: Release hormones into the bloodstream for internal communication.
    • Examples: Pineal gland, Leydig cells in testes.

Summary

• Identify epithelial tissue by finding the basement membrane, then apical side.
• Determine cell shape and layer organization.
• Epithelial cells facilitate functions like lining blood vessels and forming glandular structures.

Conclusion

• Encouragement to explore further histology resources.
• Thanks for watching and supporting the educational content.