Pinocytosis (Greek pinein -drinking and kytos -cell) refers to the uptake of liquids into the cell, phagocytosis to the uptake of solid substances from its surrounding medium. Both processes are summarized under the generic term endocytosis.
In contrast to phagocytosis, which is only carried out in special situations and by special cells, pinocytosis is a widespread mechanism in eukaryotic cells.
The uptake of fluid into the cytoplasm occurs in the form of small vesicles that are only 150 nm in diameter. The liquid or solute components are taken up into the cytosol of the cells. Membrane extensions enclose the substance to be taken up. They are taken up as vesicles into the cytosol of the cell and are involved in the metabolism of the cells. For example, pinocytosis plays an important role in the uptake of protein-bound lipids in hepatocytes and enterocytes.
In the reversal process, the absorbed fluids are released from the cell again (exocytosis). This cell process allows a controlled uptake of fluids and solids.
Furthermore, pinocytosis plays an important role in cell and tissue development, immune response, cell communication and signal transduction. It is also involved in signal transduction in neuronal areas. However, pathogenic microorganisms can also enter the cells via pinocytosis.