Lecture Notes: Overview of Human Body Tissues

Introduction to Tissues

• Definition: Tissues are collections of cells similar in structure performing a common or related function.
• Importance: Specialization of cells allows for the complexity of multicellular organisms like humans.
• Four Types of Tissues: Epithelial, Connective, Nervous, and Muscle tissue.

Epithelial Tissue

• Function: Covers body surfaces, lines cavities, and forms glands.
• Types:
  • Covering & Lining Epithelium: Acts as boundaries; substances entering or exiting the body pass through this.
  • Glandular Epithelium: Comprises glands in the body.
• Key Features:
  • Polarity: Distinction between apical (exposed) surface and basal (attached) surface.
  • Apical Surface: May have microvilli (for absorption/secretion) or cilia (to move substances).
  • Basal Lamina & Basement Membrane: Supportive structures of glycoproteins/collagen.
  • Cell Junctions:
    • Desmosomes: Bind cells together.
    • Tight Junctions: Block fluid flow between cells.
    • Gap Junctions: Allow ion passage for communication.
  • Avascular but Innervated: No blood vessels, but supplied by nerves.
  • Regeneration: High due to exposure to friction/injury.
• Functions: Protection, absorption, filtration, excretion, secretion, sensory reception.

Classification of Epithelial Cells

• Layers:
  • Simple Epithelium: Single cell layer.
  • Stratified Epithelium: Multiple cell layers.
• Shapes:
  • Squamous: Flat, scale-like.
  • Cuboidal: Box-like.
  • Columnar: Tall, column-like.
• Combinations:
  • Simple Squamous Epithelium: Single layer of flat cells (e.g., rapid diffusion sites).
  • Simple Cuboidal Epithelium: Boxy cells, suited for secretion/absorption.
  • Simple Columnar Epithelium: Tall cells, suited for absorption/secretion.
  • Pseudostratified Columnar Epithelium: Appears stratified due to staggered nuclei.
  • Stratified Squamous Epithelium: Protective, multiple layers (e.g., skin surface).
  • Stratified Cuboidal/Columnar Epithelium: Rare, found in some glands.
  • Transitional Epithelium: Stretches to accommodate fluid (e.g., bladder).

Glandular Epithelium

• Function: Secretes specific substances like hormones.
• Types:
  • Exocrine Glands: Secrete through ducts onto epithelial surfaces.
  • Endocrine Glands: Secrete directly into the blood.

Conclusion

• Next Topic: Connective tissue.

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