Lecture on Epithelial Tissue

Introduction

• Epithelial tissue is one of the four types of tissue in the human body.
• Found everywhere from the inside of the heart to the skin.
• Important for understanding how microscopic anatomy influences visible anatomy.

Main Functions of Epithelium

• Covering Surfaces: Forms layers of cells that cover internal and external surfaces (e.g., blood vessels, skin).
• Secretion: Secreting substances within or outside the body.
• Functional Bulk of Organs: E.g., 80% of the liver by mass is epithelial liver cells (hepatocytes).

Characteristics of Epithelial Cells

• Polarity: Cells have distinct top (apical) and bottom (basal) poles.
• Basement Membrane: Separates epithelial cells from surrounding structures.
• Lamina Propria: Below basement membrane, provides nutrients and oxygen via diffusion.
• Cell Communication: Through lateral faces, gap junctions, tight junctions, and desmosomes.

Types of Epithelial Cells

• Squamous: Flat, pancake-like; thin nucleus, few organelles.
• Cuboidal: Cube-shaped; large, round nuclei, many organelles.
• Columnar: Column-shaped; often specialized for tasks like mucus secretion.

Organization of Epithelial Cells

• Simple Epithelium: Single layer of cells.
  • Simple Squamous: Lines blood vessels, allows substance passage.
  • Simple Cuboidal: Found in secretion sites, e.g., seminiferous tubules.
  • Simple Columnar: Found in GI tract, involved in secretion and absorption.
• Pseudostratified Epithelium: Appears multilayered, but all cells touch the basement membrane.
• Stratified Epithelium: Multiple layers, e.g., skin's keratinized epithelium (dead cells).
• Transitional Epithelium: Found in stretchy organs like the bladder.

Glandular Epithelium

• Endocrine Glands: Release hormones into the bloodstream.
  • Example: Pineal gland secretes melatonin.
  • Example: Leydig cells in testes secrete testosterone.
• Exocrine Glands: Release substances outside the body or into body cavities.
  • Example: Goblet cells secrete mucus in the GI tract.
  • Example: Salivary glands secrete enzymes into saliva.

Summary

• Identify basement membrane and apical side in histology slides.
• Determine cell shape and organization.

Additional Resources

• Additional videos on digestive histology and a histology playlist.
• Support via Patreon for further learning materials.

Conclusion

• Epithelial tissue has diverse roles from protection to hormone secretion.
• Understanding its structure aids in understanding its function.