In acute inflammation—the kind nature designed to help your body—the body accomplishes two goals: it creates a barrier to protect against the spread of infection from the injury, and it heals damaged tissues. Pain, redness, swelling, and warmth occur, often resulting in some loss of function. Even though the injury site may look as if something has gone terribly wrong, this inflammation process is designed to help your body.
Any injury will trigger an immediate and acute response, a short-term means of managing the situation. Let’s look at this with an old-style military battle analogy. (Last century. Modern warfare is something I have no understanding of.)
Imagine the setup
To begin, imagine the setup. First responders (white blood cells) constantly prowl through your bloodstream awaiting any attack from any direction. In addition to first responders, the bloodstream also carries fluid called exudate that can quickly be sent to any attacked location. Exudate is like the military supply water that carries everything necessary for a successful first response.
The enemy attacks!
The enemy attacks. Boom! Chemical mediators tell the nearest blood vessels to increase their permeability so that within seconds, exudate fluid and white blood cells can leak out of the blood vessel and quickly arrive at the scene of the attack. In fact, capillary (very small blood vessels) pathways are quickly built to the attack scene so that repair materials can be delivered. It’s as if the Army Corps of Engineers is building roads to the attack scene, but in this case it’s endothelial cells building capillaries and creating the pathways.
The first responders to arrive at any attack or injury are generalists, and as such, they devour all potential invaders. They aren’t looking for any particularly specific threat yet—they will take down anything that remotely looks like a threat. As these first responders are devouring enemy cells, exudate is also filling the injury site with salts and fluid to carry in repair supplies as well as to bring in more specific fighters. Blood flow to the attacked area is increased, and the body tissue surrounding the injury consequently begins to swell, stopping the blood flow and thereby keeping the fighting contained. This swelling traps enemy attackers so they don’t spread. Warmth (created by increased movement of the blood), redness and swelling are all results of the rush of fluid and blood cells to the injury site and their activities once they arrive.