In some cells, processes occur that allow particles (solid or liquid) to enter the external medium into the cell. These processes are generically called endocytosis and usually occur in cells that constitute unicellular organisms living in the aqueous medium.
Some cells of multicellular organisms can also perform these processes, but in this case the function is not food but defense. Endocytosis can occur in two ways: phagocytosis or pinocytosis.
Process used by the cell to encompass solid particles that will serve as food. The cell produces expansions of the plasma membrane (pseudopods) that surround and encompass the particles. First, the particle is in a bag named after phagosome. Then this bag joins the lysosome, (which contains digestive enzymes), so that digestion happens and useful materials are harnessed by the cell. This second scholarship is named after digestive vacuole and the whole process is called intracellular digestion heterophagic.
When the process of intracellular digestion occurs without the digested material coming from outside through phagocytosis, that is, when it digests material from the cell itself (like old degenerating organelles) it is spoken of. autophagic intracellular digestion and the vacuoles are called autophagic vacuoles. Autophageal intracellular digestion is related to an important eukaryotic cell mechanism called apoptosis, also called cellular suicide. This process is nothing more than the programmed death of a normally occurring cell, because throughout development many cells die as a normal part of the process.
Programmed death is essential for the development and functioning of various tissues.
When cells that are no longer useful lose their ability to self-destruct, they lose their function and form cell masses like tumors.
In both cases, undigested material remains inside the membranous pouch, which is called residual vacuole and can then be eliminated from the cell. Amoebas and protozoans, for example, use the phagocytosis process to capture food particles that, once inside the cell, are digested in this process. In our bodies, some white blood cells use phagocytosis to encompass invading microorganisms, such as bacteria, inactivating them.
A process similar to phagocytosis, whereby certain cells ingest fluids or small particles through tiny channels that form in their plasma membrane. When the edges of this channel close, containing the food inside, a membranous pocket called pinosome. Later these materials are digested and harnessed by the cell. In the human organism, for example, it is through the process of pinocytosis that small intestine cells capture lipid droplets resulting from digestion.
The reverse path can also be traveled by certain substances that must be eliminated from the cell in unicellular organisms. This occurs, for example, through a process called chasmocytosis and that ensures the elimination of undigested cell waste. Residues encased in a membranous pouch are carried to the plasma membrane, where the pouch fuses with it, eliminating its contents to the outside of the cell in aqueous media, in a process reverse to what occurs in phagocytosis.