Connective Tissue Classifications and Structures

Primary Functions: Structural support, binding structures together, fat storage, exchange of nutrients and metabolic waste, and defense/protection.
Basic Components: Cells, protein fibers, and ground substance.
Extracellular Matrix (ECM): Formed by the combination of protein fibers and ground substance.
Broad Categories: Connective tissue proper, supporting connective tissue, and fluid connective tissue.

Loose Connective Tissue: Contains abundant ground substance with scattered cells and loosely arranged fibers.
- Areolar Connective Tissue: Located in subcutaneous layer and around organs; contains gel-like ground substance, blood vessels, and fibroblasts.
- Adipose Connective Tissue: Located in subcutaneous tissue and around organs; composed of closely packed adipocytes (fat cells).
- Reticular Connective Tissue: Forms the stroma (framework) of lymph nodes, spleen, thymus, and bone marrow; composed of reticular fibers (branched collagen), fibroblasts, and leukocytes in a gel-like matrix.
Dense Connective Tissue: Contains tightly packed fibers with few cells and little ground substance.
- Dense Regular Connective Tissue: Forms tendons and most ligaments; composed of densely packed parallel collagen fibers with interspaced fibroblasts.
- Dense Irregular Connective Tissue: Located in the dermis, periosteum, perichondrium, and organ capsules; composed of randomly arranged collagen fibers with interspersed fibroblasts.
- Elastic Connective Tissue: Located in elastic artery walls, trachea, bronchi, and vocal cords; composed of branching elastic fibers (elastin protein) that stretch and recoil.

Cartilage: Features a semisolid extracellular matrix that provides flexibility.
- Hyaline Cartilage: Most common type; located on articular surfaces of synovial joints, larynx, trachea, and nose; contains chondrocytes in lacunae; usually covered by perichondrium (dense irregular connective tissue sheath).
- Elastic Cartilage: Located in the external ear and epiglottis; contains a web-like mesh of elastic fibers surrounding chondrocytes in lacunae; usually covered by perichondrium.
- Fibrocartilage: Located in intervertebral discs, pubic symphysis, and knee menisci; contains irregular collagen fiber bundles with chondrocytes in lacunae arranged in parallel rows; lacks a perichondrium.
Bone (Osseous Connective Tissue): Features a solid, rigid matrix for strong support.
- Compact Bone: Forms the hard outer shell; composed of osteons (cylindrical structures) made of concentric lamellae, central canals, canaliculi, and osteocytes in lacunae.
- Spongy (Cancellous) Bone: Located inside bones; composed of a network of slender bony plates called trabeculae containing bone marrow, blood vessels, and scattered osteocytes; lacks osteons.

Blood: Composed of a watery ground substance containing dissolved protein fibers.
Formed Elements: Includes cells and cell fragments:
- Erythrocytes (red blood cells)
- Leukocytes (white blood cells)
- Platelets