Introduction
Phagocytosis is the biological process by which a cell ingests and subsequently breaks down a particle within it. The term "phagocytosis" is derived from the Greek words phago- meaning "devouring," and cyte, meaning "cell". Immune system cells use phagocytosis to consume intruders like bacteria and to eliminate cell debris. Amoebas and other single-celled organisms use phagocytosis to acquire nutrients by ingesting and digesting them.
Phagocytosis can be impaired in certain diseases, such as chronic granulomatous disease, in which phagocytes are unable to produce the reactive oxygen species needed for bacterial killing. On the other hand, an excessive amount of phagocytosis may cause harm to tissues and result in autoimmune disorders like systemic lupus erythematosus.
What Is the Function of Phagocytosis?
Phagocytosis is a process in which cells actively take in solid particles into the cell through endocytosis, which is different from passive diffusion across the cell membrane. Larger molecules that cannot pass through the cell membrane easily require endocytosis, which encompasses phagocytosis, pinocytosis, and receptor-mediated endocytosis.
Pinocytosis differs from phagocytosis because it involves the ingestion of liquid droplets rather than solid particles. Phagocytosis is used by cells in the immune system to engulf and eliminate invading pathogens such as bacteria and viruses. In some single-celled organisms like amoebas, phagocytosis is used to acquire nutrients by ingesting food particles that are then digested by lysosomes. Pinocytosis, however, involves the ingestion of small particles that do not require lysosomal digestion and are directly assimilated into the cell. In general, phagocytosis is a vital process that promotes the survival and well-being of organisms.
What Are the Types of Phagocytosis?
White blood cells commonly phagocytose a variety of particles, such as bacteria, dead cells, protozoa, dust particles, pigments, and other tiny foreign bodies. In vertebrates, including humans, the most effective phagocytic cells are macrophages, which are large phagocytic cells, and neutrophils, a type of granulocyte. Macrophages are present in the lungs, liver, spleen, and lymph nodes, where they function to remove bacteria and other particles from the airways, blood, and lymph. They are also found in all tissues as wandering amoeboid cells, while monocytes, which are precursors of macrophages, are present in the blood. The smaller phagocytes, on the other hand, are primarily neutrophils that are transported through the circulating blood until they reach an infected tissue, where they penetrate the blood vessel wall and reside in that tissue. Both macrophages and neutrophils are attracted to an area of infection or inflammation caused by substances released by the bacteria and the infected tissue, or through a chemical interaction between the bacteria and the complement system of blood serum proteins. Additionally, neutrophils can accidentally collide with particles and then engulf them.
What Are the Different Steps of Phagocytosis?
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Step 1: Phagocytosis begins with the activation of a cell that will carry out the process. This could be an immune cell like a phagocyte or a single-celled organism such as an amoeba. When immune cells come across bacterial cells or their constituents, they become activated. Receptors on the cell surface bind to these molecules, triggering a response.
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Step 2: Within the immune system, chemotaxis can take place as phagocytes move towards regions of higher molecular concentration. The cells pick up chemical signals and migrate toward invading bacteria or damaged cells.
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Step 3: For ingestion to occur, it is crucial that the cell attaches itself to the particle it intends to ingest. However, certain strains of bacteria can resist this adhesion process, making it difficult for the cell to engulf and subsequently destroy them.
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Step 4: The particle is then ingested by the cell, and a vesicle called a phagosome encloses it. The phagosome transports the particle into the cell.
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Step 5: The phagosome combines with the lysosome, and the substance is decomposed by hydrolytic enzymes present within the lysosome. This fusion of phagosome and lysosome is referred to as a phagolysosome.
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Step 6: Finally, any cellular waste products that the cell cannot reuse are discharged from the cell through exocytosis. Exocytosis is the process where waste products travel in vesicles to the surface of the cell membrane and are released outside the cell. This is the opposite of endocytosis, which is how cells ingest molecules.
What Is the Process Involved in Particle Engulfment and Digestion in Phagocytosis?
The speed of phagocytosis by a cell varies depending on the size of the particle being ingested. Small particles, like bacteria or tiny charcoal particles, are ingested almost immediately, while larger objects like clumps of bacteria or tissue cells require a more prolonged response. The cell surrounds the object until it is completely engulfed, forming a phagosome - a membrane-bound vacuole. The ingested particle is then digested by hydrolytic enzymes that are contained within lysosomes, which are membrane-enclosed sacs found within the cell. Phagocytic enzymes are secreted into the vacuole, where digestion occurs, and the small organic components of the particle are utilized to build larger molecules that are needed by the cell.
What Is an Example of Phagocytosis?
An example of phagocytosis can be seen in the process of macrophages engulfing and digesting invading bacteria in the human body. Specialized immune cells called macrophages can function as phagocytes and identify pathogens when they invade the body detected by macrophages, which are specialized immune cells that act as phagocytes. The macrophages recognize the foreign object and move towards it, extending their pseudopodia to engulf it.
Once the bacterium is surrounded by the pseudopodia, the macrophage pulls it inside, forming a membrane-bound compartment called a phagosome. Afterward, the phagosome combines with a lysosome, which is an organelle enclosed in a membrane that holds digestive enzymes. membrane-bound organelle containing digestive enzymes. The enzymes break down the bacterium into smaller pieces, which can be utilized by the macrophage for energy or eliminated from the body as waste.
This process of phagocytosis plays a critical role in the body's defense against invading pathogens. It helps prevent infections and protect the body from harmful bacteria and other foreign particles. Without phagocytosis, the body would be more vulnerable to infections and diseases.
Conclusion
In conclusion, phagocytosis is a critical process for the survival and well-being of organisms. It is a mechanism by which cells actively take in solid particles into the cell through endocytosis. Larger molecules that cannot pass through the cell membrane easily require endocytosis, which encompasses phagocytosis, pinocytosis, and receptor-mediated endocytosis. Immune system cells, such as macrophages and neutrophils, use phagocytosis to engulf and eliminate invading pathogens like bacteria and viruses. Amoebas and other single-celled organisms use phagocytosis to acquire nutrients by ingestion and digestion of particles. However, impaired or excessive phagocytosis can lead to diseases and tissue damage. The six steps of phagocytosis include activation, chemotaxis, attachment, ingestion, fusion, and exocytosis.
