Tissue Lecture Part 1 Notes

Definition and Composition of Tissues

• Tissues are groups of closely associated cells working together for a common function.
• Composed of cells, fibers, and fluid; not just cells.

Four Major Categories of Tissues

1. Epithelial Tissue

   • Function: Covering or lining parts of the body.
   • Example: Skin (epidermis) covers the body; lining of stomach.
   • Derived glands: Sweat glands, salivary glands, mammary glands.

2. Connective Tissue

   • Function: Binding and supporting other tissues and organs.
   • Examples: Bone (solid), blood (liquid).

3. Nervous Tissue

   • Function: Communication and control within the body.
   • Components: Neurons and supporting cells.
   • Examples: Brain, spinal cord, nerves.

4. Muscle Tissue

   • Function: Movement.
   • Types: Skeletal, cardiac, smooth.

Hierarchy of Structures

• Cells → Tissues → Organs
  • Example: Stomach as an organ has different tissues to perform functions.

Focus of Study: Epithelial and Connective Tissues

• Main focus on epithelial and connective tissues in detail.
• Nervous and muscle tissues covered in separate packets.

Epithelial Tissue (Epithelium)

• Covers or lines body parts, forming a continuous sheet of cells.
• Functions include absorption, secretion, protection, sensory reception, and filtration.

Characteristics of Epithelial Tissue

1. Cellularity - Composed almost entirely of cells.
2. Special Contacts - Cells joined by special cell junctions.
3. Polarity - Apical (free) and basal (attached) surfaces.
4. Supported by Connective Tissue
5. Avascular but Innervated - No blood vessels; may have nerve endings.
6. High Regenerative Capacity - Rapid replacement of lost cells.

Classification of Epithelial Tissue

• Based on number of cell layers:
  • Simple (single layer) vs. Stratified (multiple layers)
• Based on cell shape:
  • Squamous (flat), cuboidal (cube-like), columnar (tall)

Special Types of Epithelium

• Pseudostratified: Appears stratified but is a single layer with varying cell heights.
• Transitional: Found in urinary organs, allows stretching (e.g., bladder distension).

Functions Based on Structure

• Simple Epithelia: Thin, for absorption and secretion.
• Stratified Epithelia: Thick, for protection.
• Simple Squamous: Passive diffusion and filtration.
• Simple Cuboidal/Columnar: Secretion and absorption.

Glands Derived from Epithelium

• Exocrine Glands: Secrete externally, have ducts.
• Endocrine Glands: Ductless, secrete hormones into bloodstream.
• Unicellular Glands: Goblet cells, secrete mucus.
• Multicellular Glands: Classified by duct structure (simple or compound) and secretory unit shape (tubular, alveolar).

Cell Junctions

• Tight Junctions: Prevent passage between cells.
• Adherens Junctions: Bind cells together.
• Desmosomes: Strong adhesion, resist tension.
• Gap Junctions: Allow communication between cells.

Basal and Apical Surface Structures

• Basal Lamina: Non-cellular support layer, filters molecules.
• Microvilli (apical): Increase surface area for absorption.
• Cilia (apical): Motile, move substances over epithelial surfaces.

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In the next part, the focus will be on connective tissue.