Pinocytosis - One More TimeSimply put, cells need to eat and drink just like you. Phagocytosis is the process of a cell eating. It is one type of endocytosis. Endocytosis happens when a cell goes out and takes in something. Phagocytosis is the situation when it gets a solid. Pinocytosis is the act of grabbing some liquid. The whole cell works during the process. It is not just some membrane proteins taking in a couple of molecules as in active transport.
You Gotta HydrateAlmost all cells do some form of pinocytosis. The process does not require the cell to go out and hunt down prey as in phagocytosis. It's about taking in drops of fluid that are outside of the cell. All cells need to do that. There are even different styles of pinocytosis. Cells have certain styles depending on what structures they have.
Basic pinocytosis involves a cell taking in very small drops of extracellular fluids. Many organelles pinch off vesicles into the cytosol. Pinocytosis sees the cell membrane wrap around a drop and pinch it off into the cell. The molecules inside of the newly created vesicles can then be digested or absorbed into the cytosol.
Pinocytosis is a process that is happening all of the time. An amoeba may form the vesicles easily as it moves along. A cell with many microvilli (like in your intestine) is constantly pinching off little vesicles filled with fluid. Those types of cells never move so they need to be more efficient.
Endocytosis and Accumulation (US-NIH Video)