L40: the extracellular matrix

• What is the extracellular matrix (ECM)?

  A major product of the secretory pathway
• Why is the extracellular matrix relevant?

  It holds cells together and anchors cytoskeleton
• What is the composition of the extracellular matrix in animals?

  Made of proteins and polysaccharides
• Where is the extracellular matrix present in animals?

  In dense and loose connective tissues
• What is the primary mechanical role of the ECM in dense connective tissues?

  The matrix is thick and provides strength
• How does the ECM function in loose connective tissues?

  The matrix is thin, connecting cells via junctions
• What are the roles of the extracellular matrix?

  Supports cells, influences behavior and function
• What is turgor in the context of the ECM?

  Internal tension in a tissue
• How does the ECM help absorb impact?

  By creating turgor and providing scaffolding
• Who secretes ECM molecules in loose connective tissue?

  Fibroblasts
• Who secretes ECM molecules in bone?

  Osteoblasts
• Who secretes ECM molecules in cartilage?

  Chondrocytes
• What fills the spaces around cells in the ECM?

  Secreted molecules that form a gel
• What are glycosaminoglycans (GAGs)?

  Polysaccharides that form long linear chains
• How do GAGs create turgor?

  By attracting cations and water into the matrix
• What is the main type of collagen in the body?

  Type I collagen
• What is the structure of fibrillar collagen?

  Trimeric fibril structure
• What is the role of the N-terminal propeptide in collagen?

  Keeps trimers apart to prevent fibril formation
• What happens to collagen just prior to secretion?

  Individual tropocollagens are crosslinked to form fibrils
• How are collagen fibrils arranged in skin?

  Like wickerwork for elasticity
• What is a fibripositor?

  Tubular extensions that accept collagen carriers
• How are collagen fibrils arranged in bone?

  In a plywood arrangement for strength
• How do collagen fibrils behave in tendons?

  Aggregate to form a supercable for strength
• How does collagen contribute to the properties of skin?

  Provides elasticity and structure
• How does collagen contribute to the properties of bone?

  Provides stiffness, strength, and toughness
• How does collagen contribute to the properties of tendons?

  Allows stretching without breaking
• What is the size range of collagen fibrils?

  10-300 nm
• What is a fibripositor?

  It is a Golgi to PM carrier.
• What do fibripositors do?

  They accept GPCs containing collagen.
• How does a closed fibripositor function?

  It fuses with the PM to extrude collagen.
• How are collagen fibrils arranged in the ECM?

  They line up in register.
• Why does young skin spring back into shape?

  Due to collagen fibrils arranged like wickerwork.
• What is the arrangement of collagen fibrils in bone?

  They have a "plywood" arrangement.
• Why are collagen fibrils in bone important?

  They provide stiffness, strength, and toughness.
• How do collagen fibrils in tendons behave?

  They aggregate to form a supercable.
• What is the function of tendons?

  They connect muscle to bone.
• How can collagen fibrils take on different arrangements?

  Through interactions with other ECM molecules.
• What is type IX collagen?

  A fibril-associated collagen interacting with type II.
• What is type XII collagen?

  A fibril-associated collagen interacting with type I.
• What is perlecan?

  It is a long, snaky proteoglycan.