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Exocytosis: important biological process that occurs in cells
Introduction (what they are)
Endocytosis and exocytosis are procedures through which elements (molecules, substances, living things) cross the membrane of cells. In the case of endocytosis, the element goes from the outside into the cell. In exocytosis, however, it is transferred from the cellular interior to the exterior.
Phagocytosis is a type of endocytosis, being known as "cell food". It is the form of nutrition used by unicellular microorganisms such as bacteria and protozoa. It is also the form of action of the defense cells.
Main features (summary)
In both endocytosis and exocytosis, substances pass through the plasma membrane with the aid of vesicles. But each process has its particularities:
- In endocytosis, a substance adheres to the outside of the plasma membrane. The part of the membrane that is in contact with the substance folds inward and encompasses the contents. Then the bladder that forms detaches from the membrane and moves through the cytoplasm.
Excretion of residues and release of substances such as hormones are done by exocytosis: a cytoplasmic vesicle containing a compound to be removed moves to the inner surface of the plasma membrane. The gallbladder wall fuses with the plasma membrane and the gallbladder contents are released outside.
Participating in cytoplasmic membrane selectivity
The plasma membrane is judicious. It is permeable, but selects which molecules and substances will pass from side to side. Some cross the plasma membrane easily, others enter or exit slowly, and others do not enter at all. If it were not for this property, cells would not retain their integrity.
Endocytosis and exocytosis are important mechanisms that participate in this selection power. Because they are energy-consuming processes, they are in the active transport category. The other mechanisms that allow plasma membrane transposition are diffusion and mediation transport.
Blood cells called neutrophils use endocytosis and exocytosis to fight pathogenic bacteria. A bacterium is engulfed by the degraded plasma membrane and the residues of that death are expelled out of the neutrophil.