Interstitium: Interstitial fluid facilitates nutrient and waste diffusion.
Composition: High amounts of extracellular matrix (ECM) made of fibers (collagen, elastin) and ground substance (proteoglycans, GAGs).
Origin: All connective tissues derive from embryonic mesenchyme, a viscous matrix with sparse collagen.
Cells of Connective Tissue
Fibroblasts: Produce and maintain ECM components including collagen and elastin.
Adipocytes: Store fat, providing insulation and cushioning.
Macrophages: Derived from monocytes; involved in phagocytosis and tissue repair.
Mast Cells: Release histamine and other mediators during inflammatory responses.
Plasma Cells: Derived from B lymphocytes; secrete antibodies for immune defense.
Leukocytes: White blood cells that provide immune surveillance.
Fibers of Connective Tissue
Collagen: Most abundant protein, essential for strength and structural integrity. Types include fibrillar (Type I, II, III), network-forming (Type IV), and linking/anchoring (Type VII).
Reticular Fibers: Composed of Type III collagen; support cells in lymphoid and hematopoietic tissues.
Elastic Fibers: Composed of elastin, providing stretchability; important in skin, lungs, and large blood vessels.
Ground Substance
Composition: Mixture of glycosaminoglycans (GAGs), proteoglycans, and multiadhesive glycoproteins (e.g., fibronectin, laminin).
Function: Provides hydration, facilitates diffusion of molecules, and supports cell adhesion.
Key GAGs: Hyaluronan, chondroitin sulfate, keratan sulfate; vary in size and function.
Types of Connective Tissue
Connective Tissue Proper:
Loose: More ground substance than fibers; supports organs and fills spaces.
Dense: Rich in collagen fibers; types include dense irregular (resists tension) and dense regular (provides strength in one direction).
Reticular Tissue: Delicate networks supporting cells in lymphoid organs.
Mucoid Tissue: Gel-like, primarily found in umbilical cord; contains abundant hyaluronan.