Anatomy and Physiology: Tissue Types and Classification

Levels of Organization

• The body's organization progresses from least to most inclusive:
  • Atoms
  • Molecules
  • Cells
  • Tissues (Current chapter focus)
  • Organs
  • Organ systems
  • Organism
• This hierarchy is critical because tissue characteristics and functions are specific to the organs they form (e.g., heart tissue is different from kidney tissue due to varying functions).

Four Major Tissue Types

• Tissues are divided into four main categories, ordered sequentially in the body from superficial to deep:
  1. Epithelial Tissue: Most superficial.
  2. Connective Tissue: Beneath epithelial.
  3. Muscular Tissue: Underneath connective.
  4. Nervous Tissue: The deepest layer.

Epithelial Tissue: General Characteristics

• Location: Most superficial tissue, found everywhere in the body, including internal organs and glands (e.g., sweat glands, sebaceous glands, mucous glands).
• Functions: Primarily involved in absorption, protection, and excretion.
• Vascularity: Avascular; it does not have its own blood supply. This means nutrients must diffuse from underlying tissues.
• Regeneration: Epithelial cells readily divide (by mitosis), allowing for rapid healing and replacement when injured (e.g., skin cuts).

Example: Skin Layers and Tissue Types

• The skin has three main layers:
  • Epidermis: The most superficial layer, composed of epithelial tissue. Lacks blood supply.
  • Dermis: Located beneath the epidermis, composed of connective tissue. This layer contains blood supply; cutting into the dermis results in bleeding.
  • Hypodermis: Connects the skin to underlying muscles.

Cell Junctions

• Purpose: Tissues are made of cells, and these cells need