Lecture Notes: Epithelial Tissue and Histology

Introduction

• Epithelial tissue: One of four tissue types in the human body.
• Found from the inside of hearts to skin surface.

Importance of Epithelial Tissue

• Less body mass compared to muscle/connective tissue but located in crucial spots.
• Main Functions:
  1. Form layers covering internal/external surfaces (e.g., lining of blood vessels and skin).
  2. Secrete substances within or outside the body.
• Example: Liver is 80% epithelial liver cells (hepatocytes).
• Acts as protective layers and secreting cells.

Characteristics of Epithelial Cells

• Polarity:
  • Distinct top (apical pole) and bottom (basal pole) separated by basement membrane.
  • Apical pole faces lumen; can have cilia.
• Below basement membrane: Lamina Propria
  • Contains connective tissue and blood vessels.
• Lateral Faces:
  • Allow communication between cells (gap junctions, tight junctions, desmosomes).

Histology and Organization

• Avascular:
  • Depends on diffusion from capillaries for nutrients and oxygen.
• Rapid Skin Cell Replacement:
  • Due to fast nutrient diffusion.
• Layers Identification:
  • Identify basement membrane, apical side.
• Cell Shapes:
  • Squamous (flat), Cuboidal (cube-shaped), Columnar (tall and cylindrical).

Types of Epithelial Tissue

• Simple Epithelium: Single layer.
  • Simple squamous (e.g., blood vessels).
  • Simple cuboidal (e.g., seminiferous tubules).
  • Simple columnar (e.g., gastrointestinal tract).
• Pseudostratified Epithelium: Appears multi-layered but single.
  • Example: Found in respiratory system.
• Stratified Epithelium: Two or more layers.
  • Keratinized: Dead, keratin-filled cells (e.g., skin).
  • Transitional Epithelium: For stretchy tissue (e.g., bladder).

Glandular Epithelium

• Endocrine Glands:
  • Secrete hormones into the bloodstream.
  • Example: Pineal gland in the brain (produces melatonin).
• Exocrine Glands:
  • Secrete substances outside the body or into body cavities.
  • Examples: Goblet cells (GI tract), salivary glands, apocrine glands (odorants).

Summary

• Identifying Epithelium in Slides:
  • Find basement membrane and apical side.
  • Differentiate cell shape and organization.

Conclusion

• Note: Epithelial cells in digestive system are significant.
• Video playlist available for further histology learning.
• Support via Patreon or sharing resources with students.