Structural Biochemistry/Pinocytosis

In pinocytosis, the cell “gulps” droplets of extracellular fluid into tiny vesicles. It is not the fluid itself that is needed by the cell, but the molecules dissolved in the droplets. Because any and all included solutes are taken into the cell, pinocytosis is nonspecific in the substances it transports. In contrast to phagocytosis referring to "cell-eating", pinocytosis refers to "cell drinking". The hydrolysis of food inside vacuoles, called intracellular digestion, begins after a cell engulfs solid food by phagocytosis or liquid food by pinocytosis. In the process of pinocytosis, the plasma membrane forms an invagination and any substance found within the area of invagination is then brought into the cell. Generally, this material will be dissolved in water and thus this process is also referred to as "cell drinking" to indicate that liquids and material dissolved in liquids are ingested by the cell. This is opposed to the ingestion of large particulate material like bacteria or other cells or cell debris.

In essence, pinocytosis adsorbs extracellular fluids for the nutrients and material broken down in the fluid. This process is takes energy in the form of adenosine triphosphate. It is also a method of ingestion that is less selective than phagocytosis. It is less selective in that it basically just adsorbs all fluid in its immediate environment. Basically, pinocytosis is unspecific to what it transports, while phagocytosis is careful in choosing food particles to engulf.