man standing in front of fire

How Does the Inflammatory Process Work? Purpose, Signs, Triggers, etc.

In this article I will be explaining what is inflammation, what is the purpose of inflammation, what are the signs and symptoms of inflammation, what triggers inflammation, what happens during the inflammation, and so on.

What is inflammation?

So let’s start by asking, “What is Inflammation?”. Well, inflammation is the body’s protective response to harmful stimuli such as foreign invaders like bacteria and viruses, damaged cells such as from physical trauma, and irritants such as the capsaicin chemical inside hot chili peppers. Inflammation may also be triggered by allergies and certain foods that a person is allergic to.

What is the purpose of inflammation?

The purpose of inflammation is to remove the harmful stimuli from the body and clean up operations such as removing the the dead, dying, and damage cells from the site of inflammation. Further, inflammation sets up the stage for the repair of the tissue.

Another function of inflammation is to prevent further damage to the affected part of the body. For example, let’s say a boy sprains his ankle. Very soon after, the boy’s ankle would immediately start getting inflamed and swollen, preventing further movement. This is actually good thing, as the swelling & inflammation stiffens the joint, and becomes painful to prevent further movement of the joint and to allow for proper healing.

What are Signs & Symptoms of inflammation?

Well, the primary signs and symptoms that show that inflammation is occurring in the affect body tissue includes:

  • Heat and Redness, given that blood circulation increases to the site of injury
  • Swelling, which may cause a loss of function given that swelling restricts movement.
  • Pain, which inhibits further use and movement of the affected body part. This helps insure that this location is not further damaged, but taken care of by the person.

What are causes or triggers for inflammation?

Inflammation can by provoke by stimuli that damages the body or triggers off the immune system.

Hot Desert Sun
Too much exposure to sunlight, especially when the sun is at its zenith, may cause sunburns and thereby cause inflamed skin.

So to list them out, the causes of inflammation include:

  • Physical trauma; i.e. blows, crush, cuts
  • Exposure to excessive sunlight; UV rays damage skin cells in excess
  • X-rays and radiation damage cells including DNA
  • Chemicals that damage the body via corrosion
  • Extreme heat or cold
  • Infections by bacteria, viruses and parasites
  • Allergens or what the immune system treats as a foreign invader

So physical trauma as a cause for inflammation is pretty straight forward. When parts of the body become damaged, or when cells die or become damaged, an inflammatory response occurs to help prepare that part of the body for healing. After all, damaged and dead cells must be removed or “sanitized” to prevent infection from bactera and fungi. When the immune system can’t keep up, you end up with necrotic tissue and gangrene.

The types of physical trauma are pretty obvious, like cuts, bruises, crushing, etc. But another type inflammation trigger is physical stress, like exercise. Exercise is good for you, given that the strain of exercise causes the body to experience an adaptive response that makes the body tougher and stronger, and maybe even the immune system as well.

But there is such a thing as too much of a good thing. Extreme amounts of exercise, or suddenly exercising more than what a person is usually used to, can inflame the body for worse. This is especially true when a person keeps exercising without adequate rest to heal the body- I suppose you can call this “over-training”. This causes systemic or chronic inflammation so long as those exercise-related injuries aren’t allowed to heal.

What happens during inflammation?

Let’s outline the whole inflammatory process to really understand what happens during inflammation:

  1. Immune system triggers off
  2. Size of blood vessels increase for inflamed area
  3. Capillary permeability increases for inflame area
  4. Leukocyte exudation or extravasation a.k.a. white blood cells start oozing out

Immune System is Triggered

So the first thing that happens is that something triggers off the immune system to cause the inflammation. Such as a cut, wound, physical trauma, heavy metal exposure, pesticide exposure, and coming in contact with an irritant or allergen.

Next, the classic signs of inflammation appear, such as increased heat and redness due to increased blood circulation (I presume), swelling and loss of function as a result, as well as pain.

diagram showing capillaries, artery, arteriole, vein, venule
By National Cancer Institute, National Institutes of Health [Public domain], via Wikimedia Commons Capillaries become more permeable during inflammation to allow leukocytes, a.k.a. white blood cells, to enter the site of injury

Size of Blood Vessels

These primary signs of inflammation appear along with more subtle changes such as an increase in the size of blood vessels, specifically the dilation of arterioles, capillaries, and venular beds. The dilation of these vascular structures causes an increase rate of blood flow, but perhaps a slight decrease in blood pressure. My logic is a bigger a pipe is, the less pressure is required to pump liquid through it than a smaller pipe.

By the way, the increased blood flow from the bigger blood vessel size is one of the reasons why the inflamed area becomes hotter and redder.

Capillary Permeability

Another thing that happens is that the capillary permeability increases for the inflamed tissue, allowing protein rich fluid to seep out of the small blood vessels into the surrounding tissue. This permeability is the reason why you see edema develop in sites of inflammation.

Leukocyte Extravasation

diagram showing leukocyte extravasation
By Uwe Thormann [GFDL or CC-BY-SA-3.0], via Wikimedia Commons Neutrophil granulocyte migrates from the blood vessel to the matrix, secreting proteolytic enzymes, in order to dissolve intercellular connections (for improvement of its mobility) and envelop bacteria through Phagocytosis.
The next thing that happens during inflammation is leukocyte extravasation– in other words, white blood cells start oozing out of the blood vessels into the inflamed tissue. Leukocyte extravasation is composed of 3 parts:

  1. Margination
  2. Pavementing
  3. Emigration.

Leukocyte Margination

So the first thing that occurs is margination, which is when leukocytes or white blood cells move out to the endothelial lining of the small blood vessels.

Leukocyte Pavementing

Next pavementing occurs, which is when those white blood cells then line up tightly packed along the blood vessel endothelium; endothelium refers to the inner surface layer of cells lining the organ- which in this case is the blood vessels.

Leukocyte Emigration

Finally in emigration, the white blood cells move through the endothelium cell layer through spaces in-between, to the areas outside of the blood vessels. Note that during inflammation, the capillary endothelial wall opens up, or become more “permeable”, to allow the white blood cells and blood plasma to pass through.


At this point, the white blood cells are called to sites of inflammation by chemotaxis. Chemotaxis refers to the use of biological chemicals to call white blood cells to sites of inflammation. Usually white blood cells release cytokines at the inflamed site to attract more of the white blood cells.

Finally, these groups of white blood cells that arrive at the inflammatory site may be composed of neutrophils and macrophages, and one way they neutralize foreign threats is through phagocytosis- which is the white blood cell’s ingestion of other microbes.

Extra Notes

During inflammation, white blood cells release chemicals near the site of injury or irritation. Specifically, histamines and bradykinin are released by the white blood cells. Also when blood platelets clot together, they release the neurotransmitter serotonin to cause the constriction of the blood vessels.

Gut inflammation and fasting connection

An interesting thing about fasting is that it may improve the healing of the gut. To understand why, let’s say that you a specific type of food that you are mildly sensitive too. Eating that a couple of times a day may be a cause for near-chronic inflammation. This is bad, given that the stomach doesn’t have enough time to recover from damage done by the food. This makes your gut more sensitive and less able to handle & digest foods. But with fasting, even if you eat a food that you are mildly sensitive too, you give your stomach more time to recover from the inflammation.

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