Cell Junctions and the Extracellular Matrix
• Direct and extracellular matrix interactions are social interactions between
cells and hold cells together. These interactions make multicellular life
possible - shape, strength, architecture of a life form.
• Extracellular Matrix - a complex network of proteins and polysaccharide
chains that cells secrete.
• Cell Junctions/Extracellular Matrix have two broad categories of tissues that
are found in all animals (see below figure):
• Connective tissues - e.g. bone or tendon, are formed from an extracellular
matrix produced by cells in the matrix. The matrix that bears most of the
mechanical stress the tissue is subjected to, not the individual cells. Direct
attachments between cells are rare, but cells are attached to the matrix. Cell–
matrix junctions link the cytoskeleton to the matrix, allowing the cells to move
through the matrix and monitor changes in its mechanical properties.
• Epithelial tissues - e.g., the lining of the gut or the epidermal covering of the
skin, cells are bound together as sheets called epithelia.
• basal lamina/basement membrane - thin mat of cellular matrix within
• cell-cell junction - direct connections in the epithelium.