Cells are held together by either fibrous nets or direct connections.
Desmosomes are like small spot welds that hold adjacent cells together.
Fibers on the outer surface of each desmosome interlock with each other.
Desmosomes are anchored internally by intermediate filaments of the cytoskeleton.
Gap junctions are formed when membrane channels of adjacent plasma membranes adhere to each other.
Gap junctions form gaps or "tunnels" that join the cytoplasm of two cells.
Gap junctions fuse the two plasma membranes into a single structure.
Certain molecules can pass directly from one cell to another through gap junctions.
Impulses traveling along a membrane can travel over many cell membranes in a row without stopping because of gap junctions.
Tight junctions occur in cells that are joined by "collars" of tightly fused membrane.
Rows of membrane proteins that extend all the way around a cell fuse with similar membrane proteins in neighboring cells in tight junctions.
Tight junctions hold an entire sheet of cells together tightly.
Tight junctions occur in the lining of the intestines and other parts of the body.
Molecules cannot permeate or spread through the cracks between cells bound together by tight junctions.
The only way for a molecule to get past the intestinal lining is through a controlled channel or carrier molecules in the plasma membranes of the cells.
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