QS Study

Pinocytosis is the only means by which most large macromolecules, such as most protein molecules enter cells. It is the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane. It is used primarily for clearing extracellular fluids and as part of immune surveillance. Cells in the kidney can use pinocytosis to divide nutrients and fluids from the urine that will be excluded from the body.

Pinocytosis occurs continually at the cell membranes of most cells but especially rapidly in some cells. This process requires energy in the form of adenosine triphosphate, the chemical compound typically used as energy in the majority of animal cells.

Basic Steps of Pinocytosis

  • The plasma membrane wrinkles internal forming a depression or cavity that fills with extracellular fluid and dissolved molecules.
  • The cell membrane forms a small open-ended pocket, or invagination, around the part of the ECF that is going to be absorbed into the cell.
  • Fusion of the ends of the in-folded membrane cuts the vesicle off from the membrane, allowing the vesicle to drift towards the center of the cell.
  • The vesicle might traverse the cell and be recycled back into the membrane by exocytosis or may fuse with a lysosome. It prevents the molecules from disrupting the rest of the cell as they are transported.
  • The molecules inside the vesicle are ultimately free to be used by other parts of the cell.