Phagocytosis

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"Phagocytosis is the process of certain living cells, called phagocytes, ingesting or engulfing other cells or various particles" (Singh) The phagocytes can either be one-celled organisms, such as an amoeba.

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Various organs have their own specialized macrophages such as the liver, kidneys, and brain. Macrophages act as scavengers, going throughout the body removing worn out cells along with debris.

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A type of granulocyte is the neutrophil, they are particularly abundant in the blood (Washington.Edu). These neutrophils have a relatively short life span, lasting only hours to days.

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A type of phagocyte is a monocyte which later develops into a macrophage when they enter into tissues. Macrophages enter the tissues by squeezing between the endothelial cells.

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After destroying the microbe, the sixth step is when phagocytes distribute molecules that diffuse to surrounding cells to generate an overall response to the invading infection.

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Opsonin coated bacteria that binds to these receptors allows the cell to begin to extend pseudopods to engulf the bacteria. The third step involves the pseudopods. The two pseudopods fuse together at the tips to form a phagosome.

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Phagocytes can also be body cells, for example a leukocyte or more commonly known as a white blood cell. Among amoebas and sponges, phagocytosis is a means of feeding.

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Phagocytosis generally has 5 steps. The first is the activation of the phagocyte. In order for the macrophage to take up the microorganisms, the particle must first attach to the cell surface in turn activating one of the receptors.

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The fifth step is the actual breaking down of the microbe. Many factors contribute to the destruction of the microorganism within the phagolysosome. These factors include oxygen radicals, nitric oxide, and hydrogen ion transport, just to name a few.

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The fourth step is when the phagosome fuses with the lysosome. A lysosome's contents are primarily focused on destroying microorganisms. When the fusion is complete, there is a creation of a phagolysosome.

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The way that TNF works along with all cytokines is it binds to cell receptors and has a very different effect on different types of cells. Most cytokines are known to promote inflammation. The initial phagocytosis by the macrophages will not end the infection unless there are few microbes present.

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The second step involves antibody receptors. Antibodies are specified proteins that aid the human body in fighting off infection .Antibodies do this by bonding, or covering the surface of harmful microorganisms. The proteins that cover the microorganism are called opsonins.

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The speed in which a microbe or a microorganism is ingested all depends on the size of the particle being ingested. Small particles are ingested almost instantaneously, while larger organisms, such as bacteria or tissue cells, are ingested by a longer process by the leukocyte.

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They regulate the body's immune response, and are distributed to the neighboring cells to coordinate a response to the infection. Two of the most important cytokines that are released are TNF-alpha and interleukin-1(IL-1).

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When a phagocyte takes in a 'potentially dangerous' microorganism it is broken down through a series of compartments that have specified enzymes that can break it down in a safe way for the cell.

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After the killing of the microorganism or microbe the phagocyte releases a set of regulatory molecules. These regulatory molecules are called cytokines. "Cytokines refer to any small protein that is released to help coordinate an immune response"

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Amoeba's use pseudopodia to engulf organisms or debris from their environment. In animals, phagocytosis is a means for fighting infections and clearing the body of toxins or antigens.

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Granulocytes contain granules that have various chemicals that allow them to kill microorganisms.

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Not only do they get rid of cells and debris, they act as "antigen presenting cells" (Jennett). Macrophages produce a strong chemical signal, known as monokines, that are important to the immune system.

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The cytokines are also used to recruit other cells to help fight the infection. The first cells brought in are the neutrophils, they are present in the blood and enter the infected tissue rapidly. The neutrophils then begin more phagocytosis to kill the infection.

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TNF-alpha stands for tumor necrosis factor alpha and causes inflammation as a response to an infection, it is also prominent in promoting apoptosis and killing cells.