An amoeba showing pinocytosis.
Pinocytosis is the process by which a cell takes in extracellular fluid by the invagination of the cell membrane. Rather than entering and passing through the cell membrane as individual molecules, a droplet becomes bound to the membrane. A pocket then forms and pinches off to form a vesicle, which subsequently ruptures, releasing its contents into the cytosol. Pinocytosis ('cell drinking') is a form of endocytosis.