Tissue Level of Organization (Chapter 4)

Overview

• Hierarchical progression in biology: from atoms/molecules (Chapter 2), to organelles/cells (Chapter 3), to tissues, organs, and organ systems (future chapters).
• Definition of tissues: Collections of specialized cells and their products performing specific functions.
• Histology: The study of tissues.

Four Main Types of Tissue

1. Epithelial Tissue
2. Connective Tissue
3. Muscle Tissue
4. Nervous Tissue

Focus in This Chapter

• Mainly on Epithelial and Connective tissues.
• Brief references to Muscle and Nervous tissues for later detailed chapters.

Epithelial Tissue

• Location: Covers exposed surfaces and lines internal passageways and chambers; also forms glands.
• Functions: Protection, permeability control, sensation, and specialized secretions.
• Characteristics
  • Polarity: Has an apical (top) and basal (bottom) surface.
  • Cellularity: Cells are closely packed with cell junctions.
  • Attachment: Attached to a basement membrane.
  • Regeneration: High regenerative capacity.

Types of Epithelial Tissue

• Simple Epithelia: One cell layer thick.
• Stratified Epithelia: Multiple layers of cells.
• Shapes: Squamous (flat), cuboidal (cube-shaped), columnar (column-shaped).

Special Types of Epithelia

• Transitional Epithelia: Can stretch and is found in the bladder.
• Pseudo-stratified Columnar Epithelia: Appears stratified but all cells touch the basement membrane; found in the respiratory system.

Glands

• Endocrine glands: Release hormones directly into the bloodstream (no ducts).
• Exocrine glands: Produce secretions through ducts. Types include:
  • Merocrine: Secretions via exocytosis (e.g., salivary glands).
  • Apocrine: Part of the cell is shed with the secretion (e.g., mammary glands).
  • Holocrine: Entire cell bursts to release secretions (e.g., sebaceous glands).
• Types of Secretions: Serous (watery), mucous (mucus), mixed.

Connective Tissue

• Functions: Provide structure, transport fluids, protect organs, support other tissues, store energy, defend from microorganisms.
• Components: Specialized cells, extracellular protein fibers, and ground substance (matrix).
• Classification
  1. Connective Tissue Proper
     • Loose: More ground substance, fewer fibers (e.g., areolar, adipose, reticular tissue).
     • Dense: More fibers, less ground substance (e.g., dense regular, dense irregular, elastic tissue).
  2. Fluid Connective Tissue
     • Blood: Watery matrix called plasma; cells include red blood cells, white blood cells, and platelets.
     • Lymph: Watery matrix forming in lymphatic vessels.
  3. Supporting Connective Tissue
     • Cartilage: Firm gel matrix; types include hyaline, elastic, and fibrocartilage.
     • Bone: Rigid matrix made of calcium salts and collagen.

Membranes

• Mucous Membranes: Line passageways that communicate with the exterior.
• Serous Membranes: Line sealed internal cavities.
• Cutaneous Membranes: The skin; thick, waterproof, and dry.
• Synovial Membranes: Line joint cavities; produce synovial fluid for lubrication.

Muscle Tissue

• Function: Specialized for contraction.
• Types
  • Skeletal Muscle: Striated, voluntary, long fibers.
  • Cardiac Muscle: Striated, involuntary, branched cells found in the heart.
  • Smooth Muscle: Non-striated, involuntary, found in walls of hollow organs.

Nervous Tissue

• Function: Conduct electrical impulses.
• Components: Neurons (send/receive signals) and neuroglia (support cells).

Tissue Response to Injury

• Inflammation: Increase in blood flow to the area.
• Regeneration: Restoration of normal function.
• Age-related Changes: Slower repair and maintenance, hormonal alterations, reduced physical activity, and various tissue deteriorations (e.g., thinner epithelia, brittle bones).

Next Chapter

• Chapter 5: The Integumentary System