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Connective Tissue & Extracellular Matrix

Connective Tissue Types

  • Collagen is the most abundant protein in connective tissue, providing tensile strength and structural support.
  • Elastin gives connective tissues their elastic properties, allowing them to stretch and recoil.
  • Fibronectin is a glycoprotein that facilitates cell adhesion and migration in the extracellular matrix.
  • Laminin is a major component of basement membranes that provides structural scaffolding.

    • Connective Tissue Cells

  • Fibroblasts are the primary cells that synthesize and maintain the extracellular matrix components.
  • Chondrocytes are specialized cells found in cartilage that maintain the cartilaginous matrix.
  • Osteoblasts are bone-forming cells that secrete the organic matrix and regulate mineralization.
  • Adipocytes are specialized cells that store lipids and comprise adipose tissue.

    • Extracellular Matrix Components

  • Proteoglycans are large molecules that trap water and provide compressive strength to tissues.
  • Hyaluronic acid is a polysaccharide that forms gels and facilitates cell migration.
  • Glycosaminoglycans are long polysaccharide chains that provide hydration and spacing in the matrix.

    • Tissue Organization

  • The basement membrane is a specialized extracellular matrix that supports epithelial tissues and separates them from underlying tissues.
  • Cartilage is a flexible connective tissue that provides support and reduces friction at joints.
  • Bone matrix is the mineralized extracellular matrix that provides rigid structural support.
  • Tendons are dense connective tissues that connect muscles to bones.
  • Ligaments are connective tissues that connect bones to other bones at joints.
  • Reticular fibers are thin, branching fibers that form a supportive network in various tissues, including the liver, lymph nodes, and bone marrow.

    • Dive deeper: Type I collagen is the most abundant type found in skin, tendons, and bones, providing tensile strength. Type II collagen is primarily found in cartilage, providing support and elasticity. Type III collagen is found in reticular fibers, supporting soft tissues like blood vessels and organs. The extracellular matrix plays a crucial role in cell signaling, tissue repair, and development. The basal lamina is a specialized layer of the extracellular matrix that separates epithelial cells from underlying connective tissue, while the reticular lamina (type III collagen) provides support and anchoring fibrils like type VII collagen. Cadherens are cell adhesion molecules that mediate cell-cell interactions, while integrins are transmembrane receptors that mediate cell-extracellular matrix interactions. Focal adhesions are specialized structures where integrins bind to the extracellular matrix, linking it to the cytoskeleton.