In cell biology, molecular biology and related fields, the word extracellular (or sometimes extracellular space) means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid. The term is used in contrast to intracellular (inside the cell). The composition of the extracellular space includes metabolites, ions, proteins, and many other substances that might affect cellular function. For example, hormones act by travelling the extracellular space t… (More on Extracellular)