PINOCYTOSIS

a process by which liquid droplets are ingested by living cells. Pinocytosis is also common among many microorganisms. Rather than passing as individual molecules through the cell membrane without disrupting it, the droplet first becomes bound, or adsorbed, on the cell membrane, which then invaginates (forms a pocket) and pinches off to form a vesicle, or vacuole, in the cytoplasm. It is believed that a vesicle may carry extracellular fluid to the opposite side of the cell, where it undergoes reverse pinocytosis. A droplet of fluid could thus be transported through the cell without disturbing its cytoplasm. Alternatively, intracellular digestion of the vacuole wall would permit the droplet to mix with the cytoplasm. See also phagocytosis.