Endocytosis | Exocytosis | Vesicular Transport | Bulk Transport | Membrane Transport | Cell

Hello. Welcome to Byte Size Med. This video is on endocytosis and exocytosis. The cell membrane is a phospholipid bilayer. Stuff moves across the membrane to either get into the cell or to get out of it. Small things like ions, they can use protein channels and they can diffuse. But what about macromolecules? They need another way and that's by using vesicles. These vesicles

pinch off the membrane. If they're going to bring things into the cell, the process is endocytosis, because "endo-" is internal. And if instead the cell is throwing something out, that's by exocytosis. "Exo-" is external. And these are the methods of bulk transport. There are different kinds of endocytosis. it could be phagocytosis, pinocytosis or receptor-mediated endocytosis.

Phagocytosis means cell eating. This happens only in a few kinds of cells, like in the immune system. Neutrophils and macrophages. What do they eat? Pathogens like bacteria, tissue debris, etc. Whatever the substance may be, when the cell comes in contact with it and it wants to engulf it, it will form these extensions called pseudopods. They go around the substance, meet and fuse.

Now it gets pulled into the cell and separates from the membrane. Now this cavity lined by that phospholipid bilayer is called a Phagosome, and it's got the engulfed material inside. That needs to be broken down. Among the organelles, which one does that? The lysosome. The phagosome fuses with the lysosome to form a phagolysosome. These lysosomes have hydrolases. They

will digest the material and what remains, that's undigested, that cannot be broken down, that forms the residual body, which will then get extruded from the cell. This extrusion is by exocytosis, because the cell is throwing its contents out. So that is phagocytosis. Pinocytosis is similar, but it's different. Instead of eating, the cell is going to drink now. This is fluid phase endocytosis.