Phagocytosis: Definition, Process & Types

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  • 0:00 What is Phagocytosis?
  • 0:45 The Process of Phagocytosis
  • 2:05 Different Types of…
  • 3:50 Lesson Summary
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Lesson Transcript
Instructor: Mary Ellen Ellis
Phagocytosis is the process by which a cell engulfs material either to destroy it, to feed on it, or to get information from it. Learn how important this process is to your own immune system.

What Is Phagocytosis?

Aside from being one of the most fun words to say in science, the process of phagocytosis is pretty cool in itself. Remember the old video game Pac-Man? You guide the round, yellow character through a maze, dodging ghosts and gobbling up little dots. When Pac-Man opens his mouth and consumes one of the dots, it's a little bit like phagocytosis.

Endocytosis is a process through which a cell absorbs a particle, molecule, bacterium, or other type of matter by engulfing it. Phagocytosis refers to the engulfing of larger, solid particles. Often, the engulfed particle is another cell, like when a white blood cell, which is a part of the immune system, engulfs a bacterium to destroy it.

The Process of Phagocytosis

Let's use the example of a white blood cell engulfing an invading bacterium to illustrate the process of phagocytosis. A cell that engages in phagocytosis is called a phagocyte. First, the white blood cell has to recognize the invader and realize that it needs to be destroyed. It recognizes signal molecules released by the bacterium and is drawn toward it.

The white blood cell then has to attach its membrane to the membrane of the bacterium. It does this by using molecules called surface receptors. These are molecules embedded in the white blood cell's membrane that are designed to detect and attach to molecules in the membrane of the bacterium. The two cell membranes link up and stick together.

Once attached to each other, the membrane of the white blood cell swells outward around the bacterium and engulfs it. The membrane enclosing the bacterium pinches off, and the result is a little pouch, called a phagosome, that contains the offending bacterium inside of the white blood cell.

With the bacterium safely imprisoned inside the white blood cell, it can now be destroyed. The white blood cell brings digestive enzymes into the phagosome. These enzymes break up the bacterium, and the resulting harmless particles can either be used by the cell or released out of the cell.

Different Types of Phagocytosis

For us humans, the most important type of phagocytosis is the one that goes on in our immune systems. Cells in the immune system act as phagocytes to identify and destroy invaders that would otherwise make us sick. These include bacteria and viruses. Immune cells also act as clean-up crews. They phagocytize dead cells and cellular debris. Several different cells in the immune system act as phagocytes and play different roles:

Macrophages are large immune cells that patrol the body for invaders or dead cells to consume. They can travel through the bloodstream to seek out cells to devour. Because of their large size, macrophages are efficient phagocytes.

Monocytes are differentiated macrophages. Each type of monocyte is specific to an organ, like the liver, and remains in that organ to attack invaders.

Neutrophils are smaller cells, but are more abundant than macrophages. They travel quickly to a site of injury, such as a cut or a scrape, to gobble up any infecting bacteria.

Dendritic cells in the immune system engage in a more intelligent type of phagocytosis. They reside near the skin and the lining of the nose to take up invading cells. Instead of completely destroying them, the dendritic cells gather information from the invaders and use it to initiate a targeted immune response.

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