Connective Tissue Structure, Function, and Biological Hierarchy

Levels of Biological Organization

The hierarchy of life includes:

• Atom
• Molecule
• Cell Organelles
• Cell
• Tissue
• Organ
• Organ System
• Organism
• Population
• Ecosystem
• Biome

Connective Tissue Fundamentals

Function of Connective Tissue

Connective tissues serve to bind structures, support, protect, and fill in gaps (filler).

Characteristics of Connective Tissues

Connective tissues are characterized by:

• Cells residing inside an Extracellular Matrix (ECM).
• The ECM includes fibers and ground substance.
• The tissue is typically vascular (contains blood vessels).

General Cell Types of Connective Tissue

• Fibroblast/Fibrocyte: Fixed cells that produce matrix fibers.
• Macrophages: Wandering cells that remove dead and foreign particles.
• Mast Cells: Located near blood vessels; they prevent clotting and participate in allergic responses.

Fibers of Connective Tissue

• Collagenous Fibers:
  • Description: Thick protein fiber bundles; very strong.
  • Examples: Ligaments, tendons.
• Elastic Fibers:
  • Description: Thin protein fibers that stretch and recoil.
  • Examples: Skin, vocal cords.
• Reticular Fibers:
  • Description: Thin collagen fibers, branched.
  • Example: Spleen.

Types of Connective Tissue

The main types include: Loose/Areolar, Adipose, Dense, Cartilage, Bone, and Blood.

Adipose Tissue (Fat)

• Function: Cushions and insulates.
• Characteristics: Composed of fat storage cells.
• Cell Type: Adipocytes (fat cells), estimated 40–50 billion in number.
• Location: Subcutaneous layer, between muscles, around the heart and kidneys.

Dense Connective Tissue (Fibrous)

• Function: Provides flexible strength and connection.
• Characteristics: Features a prominent ECM, few cells, and closely packed collagen and elastic fibers.
• Cell Type: Fibrocytes.

Cartilage Tissue

• Function: Provides support, framework, and cushioning at joints.
• Characteristics: Rigid ECM. Cells (Chondrocytes) reside in lacunae (spaces), surrounded by the ECM.
• Cell Type: Chondrocytes.

Types of Cartilage

• Hyaline Cartilage: Found at the ends of bones, nose, and trachea rings.
• Elastic Cartilage: More flexible than hyaline; found in the ears and larynx.
• Fibrocartilage: Very tough shock absorber; found in vertebral disks and knees.

Bone (Osseous Connective Tissue)

• Function: Supports, protects, and provides mineral storage.
• Characteristics: Rigid ECM composed primarily of Calcium Phosphate (Ca₃(PO₄)₂) and Calcium Carbonate (CaCO₃). Collagen surrounds the cells.
• Cell Type: Osteocytes (bone cells).
• Structures:
  • Central Canal: Provides transport into the solid matrix.
  • Canaliculi: Tunnels between cells.

Blood

• Function: Transports materials throughout the body.
• Characteristic: Fluid ECM, known as Plasma.
• Cell Types:
  • Erythrocytes (red blood cells)
  • Leukocytes (white blood cells)
  • Thrombocytes (platelets)