What holds the cells together?

Answer 1

Depends on the cell.

Many cells - especially epithelial cells, which are found in a sheet, have intracellular junctions called "tight junctions", which are proteins found in the cell membranes around the edges of the cell that bond tightly to the proteins of neighbouring cells.

Other cells, that have less strong (or less permanent) adhesions to each other - like a white blood cell crawling over the epithelium of a blood vessel - use different proteins and different adhesion types.

However - much of your body is held together by the Extracellular Matrix (ECM). The ECM is a mass of insoluble proteins secreted by cells into the intracellular space: these proteins perform a number of roles, but one of the most important is structural. ECM proteins include fibronectin, laminin, and (most predominantly) collagen. The ECM acts as a sort of scaffold, holding the cells in place (like jelly beans embedded in jello, or bricks held together by mortar). Cells attach themselves to this protein scaffold by yet more adhesion proteins.

All tissues in your body have ECM in them - but in some, the ECM is the defining characteristic of that tissue: for example, cartilage is almost entirely ECM (collagen), with a few cells embedded in it.

Answer 2

Carter Closs the big fat poopyfart does. He pees and farts on it!