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Macrophages: Definition, Function & Types

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  • 0:50 What is a Macrophage?
  • 1:31 Function of a Macrophage
  • 4:44 Types of Macrophages
  • 5:42 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

A macrophage is a type of white blood cell that cleans the body of unwanted microscopic particles, such as bacteria and dead cells. Learn more about this important cell and take a quiz at the end.

What Is a Macrophage?

The world in which we live can be a messy place. Since everything in nature tends toward chaos, our lives tend to do the same. Houses become cluttered. Litter gathers along the side of the road. It's a constant job just to keep things picked up and tidy.

Interestingly enough, a similar situation is happening inside our bodies all the time. Cells are dying, bacteria are wandering in, and viruses are attempting mass takeovers. Our immune system is constantly hard at work destroying these intruders and cleaning up the mess. One cell in particular, the macrophage, is an integral part of this cleanup process. In this lesson, we'll take a closer look at the work of a macrophage and learn about its importance within the body.

A macrophage is a large white blood cell that is an important part of our immune system. The word 'macrophage' literally means 'big eater.' It's an amoeba-like organism, and its job is to clean our body of microscopic debris and invaders. A macrophage has the ability to locate and 'eat' particles, such as bacteria, viruses, fungi, and parasites.

Macrophages are born from white blood cells called monocytes, which are produced by stem cells in our bone marrow. Monocytes move through the bloodstream and when they leave the blood, they mature into macrophages. They live for months, patrolling our cells and organs and keeping them clean.

Function of a Macrophage

The macrophage accomplishes its ongoing cleanup task by engulfing unwanted particles and 'eating' them. As mentioned before, a macrophage is an amoeba-type cell. Imagine a jelly-like blob oozing along, surrounding its prey, and swallowing it. This is essentially how a macrophage works. But let's take a closer look at the actual process.

Phagocytosis
Process of Phagocytosis

A macrophage uses a process called phagocytosis to destroy and get rid of unwanted particles in the body. Phagocytosis literally means 'eat cell.' The process works like this: as the macrophage engulfs the particle, a pocket called a phagosome is formed around it. Then, enzymes are released into the phagosome by an organelle within the macrophage called a lysosome. Much like the enzymes in our own stomach are released to digest our food, the enzymes released by the lysosome digest the particle. The remaining debris, or what is left of the particle, exits the macrophage to be absorbed back into the body.

Macrophages clean up a wide variety of unwanted foreign bodies. Like a bouncer at a nightclub, these large defenders get the job done. Bacteria, viruses, fungi, and parasites are a few examples of targeted invaders. Although our body has barriers in place, such as our skin and mucous membranes that keep many of these microorganisms out, they still manage to get inside our bodies. However, any outside offender that does get in is quickly confronted by these super cleanup cells.

Another fascinating aspect of a macrophage is its ability to know which cells to destroy and which ones to leave alone. Healthy, living cells within our body have a particular set of proteins on their outer membrane. They are essentially ID tags for our cells. This is how our immune system recognizes our own cells versus foreign bodies.

Although macrophages do not distinguish between the different types of bacteria, viruses, or other outsiders, they do recognize that those particles do not belong in the body by detecting the different outer proteins. Macrophages even have the ability to detect signals sent out by bacteria, allowing them to travel to the site of infection.

But the work of the macrophage doesn't stop there. Once a virus has been engulfed and digested, for example, the macrophage displays the identifying proteins of that particular virus. A message is sent to the rest of the immune system to call for the production of antibodies specific for that particular virus. An army of fighter cells is then sent out to destroy the viruses before they can do more damage. Macrophages even attack some cancer cells.

Additionally, as previously mentioned, macrophages also clean up dead cell debris and other 'garbage' that may be lying around. Imagine a street sweeper slowly rolling down your street. Any debris or litter that is on the pavement is swept up and 'swallowed' by the truck. The result is a street free of leaves, dirt, garbage, or any other annoyance. We can picture the macrophage in a similar way when it is cleaning up cell debris.

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