Pinocytosis - Definition

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Pinocytosis, also known as Lewis' phenomenon, refers to the process of one white blood cell type, macrophages, ingesting fluid located outside the cells. This process can be described as "cell drinking", and the Greek root of the term comes, in fact, from the word "pinô" meaning "I drink". During pinocytosis, the outside wall (membrane or macrophage) bends out of shape in order to encircle a drop of fluid, it is described as forming pinocytotic vesicles that detach themselves from the membrane and are progressively pushed towards the interior of the macrophage in order to be ingested. Pinocytosis is closely related to phagocytosis, differing in that the ingested elements in the latter are solids.