Endocytosis vs Phagocytosis
There are certain mechanisms in cells that have evolved to enclose material from the extracellular environment. Vesicles derived from the plasma membrane or the invaginations of the plasma membrane enclose this extracellular material. The uptake of these materials into cytoplasmic vesicles is by 2 mechanisms; phagocytosis and endocytosis. Phagocytosis, basically, involves in taking up particulate matter. Endocytosis, basically, involves in taking up fluid or suspended particles.
Phagocytosis can be simply called cell eating. This is mainly carried out by few specialized cells that are specialized for uptake of particulate material from the surrounding. Then those materials are delivered to a lysosome. Organisms such as amoebas trap food particles and enclose them within the folds of their plasma membrane. Then those folds fuse to form a phagosome. Phagosome then fuses with a lysosome. Finally, the material is digested inside the cell. Phagocytosis that occurs in many higher organisms is a way of protective mechanisms.
Humans possess a variety of phagocytes. Mainly they are the neutrophils and macrophages. They always circulate in the blood and through tissues and phagocytize invaders, old and damaged cells etc. These are identified by the receptors that are present on the cell surface of the phagocyte. Once the unwanted materials are enclosed within the phagocyte, they are destroyed by lysozymes or oxygen free radicals in the phagosome.
Phases of phagocytosis are as follows.
Initially the phagocyte move towards the particular molecule by chemotaxis. Then it adheres to it. Then the phagocyte ingests the molecule and results in the formation of a phagosome. The phagosome then fuses with a lysosome and the unwanted molecule is digested. Useful materials are taken back to the cell, and the rest is eliminated by exocytosis. Phagocytosis is enhanced by opsonins. Opsonins coat the unwanted particles that are to be ingested by phagocytes.
Endocytosis is of 2 types. Those are bulk phase endocytosis and receptor mediated endocytosis. Bulk phase endocytosis is a nonspecific mechanism to uptake extracellular fluid. Any types of molecules that are in the enclosed fluid enter in to the cell. Receptor mediated endocytosis involves in the uptake of specific extracellular molecules. The molecules that are taken up by endocytosis enter the endocytic pathway. The endocytic pathway begins with endosomes.
Early endosomes are located generally closer to the periphery of the cell. Late endosomes are generally located closer to the nucleus of the cell. Early endosomes and late endosomes differ from each other in terms of density, pH, protein composition etc. Materials that are taken up by endocytosis are then transported to early endocomes by endocytic vesicles. Then they are sent to the late endosomes after being sorted in the early endosomes. Molecules are then directed to the lysosomes from late endosomes.
What is the difference between Phagocytosis and Endocytosis?
• Phagocytosis basically involves in taking up particulate matter.
• Endocytosis basically involves in taking up fluid.
• However, both are mechanisms to enclose material in the extracellular environment.