Stem cell debate
Phagocytosis and Pinocytosis
Some materials enter the cell by mechanisms other than simple diffusion, osmosis, or active transport. For example, phagocytosis is a form of cellular eating employed by certain types of blood cells(neutrophils and macrophages). During phagocytosis, a blood cell detects an edible object, flows to surround it with cytoplasmic arms called pseudopods, and captures it by forming a pocket of cell membrane that pinches off into the cytoplasm. Such a pocket is a endocytotic vesicle. It often fuses with other organelles, the lysosomes, which supply digestive enzymes for breaking down the ingested item. Phagocytosis usually consumes solids such as cells or parts of cells. Pinocytosis resembles phagocytosis in that it draws in a pocket of membrane, capturing, or drinking, fluid from the extracellular environment in the process.
Exocytosis is essentially the reverse of pinocytosis. It moves a droplet of materials made in the cell, wrapped in newly synthesized membrane, to the interior surface of the cell membrane. This droplet then fuses with the cell membrane, dumping its contents outside the cell. Exocytosis thus serves as a mechanism of secretion and excretion.