Endocytosis and Exocytosis
Endocytosis is the process by which substances are brought into the cell from outside by formation of membrane bound vesicles. These extra cellular substances are enclosed in a small portion of plasma membrane which invaginates and pinches off to form an intracellular vesicle. The intake of fluids by.formation of vesicles is called as pinocytosis (pinein = drink). Pinocytosis is induced by the presence of appropriate concentrations of inducer molecules which can be proteins, amino acids or certain ions in the medium surrounding the cell. The ingestion of large particles by formation of larger vesicles is known as phagocytosis (phagein = to eat). The process of phagocytosis is associated with heterophagic activity of the lysosomes such as the destruction of worn blobd cells in the liver, spleen and bone marrow. Exocytosis is the reverse sequence where the membrahous intracellular vessicle fuses with plasma membrane and releases its content to the extracellular surroundings. The best understood form of , exocytosis is secretion by the cell. As you have studied earlier, Golgi apparatus plays an important role in the formation of cytoplasmic intracellular vesicles. The membrane of these vesicles is incorporated into plasma membrane and the vesicle's contents are discharged to the exterior.