Pinocytosis

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Pinocytosis

Pinocytosis (pronounced: pɪˌnoʊsaɪˈtoʊsɪs) is a mode of endocytosis in which small particles are brought into the cell, forming an invagination, and then suspended within small vesicles. These vesicles then fuse with lysosomes to hydrolyze, or to break down, the particles. This process requires energy and is, therefore, a form of active transport.

Etymology

The term "pinocytosis" comes from the Greek words pino (meaning "drink") and cytosis (meaning "cell action"). It was first used in the mid-20th century to describe the way cells "drink" their surrounding fluid.

Process

Pinocytosis is a form of endocytosis, a process by which cells absorb molecules (such as proteins) from outside the cell by engulfing it with their cell membrane. It is one of the ways in which cells intake necessary substances from the environment.

In pinocytosis, the cell membrane invaginates, forming a cup-shaped involution into which extracellular fluid and its dissolved solutes are drawn. This involution is then pinched off to form a vesicle within the cell.

Types

There are two types of pinocytosis: fluid-phase endocytosis and adsorptive pinocytosis. In fluid-phase endocytosis, the vesicle is small and non-specific about the substances it engulfs. In adsorptive pinocytosis, the vesicle is larger and forms after the cell membrane has recognized and bound to a specific substance.

Related Terms

  • Endocytosis: The process by which cells absorb molecules from outside the cell by engulfing it with their cell membrane.
  • Phagocytosis: The process by which a cell engulfs a solid particle to form an internal compartment known as a phagosome.
  • Exocytosis: The process by which a cell directs the contents of secretory vesicles out of the cell membrane.
  • Receptor-Mediated Endocytosis: A process by which cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane.

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