When an injury happens, the body has a set reaction called the inflammatory response, which is the first step in the body’s healing process. Swelling is a key component to the inflammatory response, but there are four other characteristic signs of inflammation, too: redness, heat in the affected area, pain, and dysfunction.
After an injury, damaged cells release chemicals that cause a number of physiological reactions. One of the things these chemicals do is dilate the blood vessels in the injured area and make fluid more likely to “leak” out of the blood vessels. In turn, the dilated blood vessels trigger an increase in blood flow to the area, which then seeps plasma fluid into the space between the cells (interstitial space) outside of the blood vessels.
As the inflammation process continues, the plasma fluid that’s leaking out of the blood vessels is collecting in the interstitial space. This collecting fluid increases the tissue pressure outside of the blood vessels (relative to the pressure inside the vessels), decreasing blood flow through the injury site. The lowered rate of blood flow restricts the flow of oxygen, which causes otherwise healthy cells to die. This oxygen-deprived cellular death is called secondary injury and it increases the amount of tissue damage related to the initial injury.
This response to injury is what causes the redness, heat, swelling, pain, and dysfunction characteristic of inflammation. Redness, swelling, and heat in an injured area are all effects of the increased blood flow in the area and the presence of plasma fluid between cells. The pain affiliated with inflammation is caused by cellular damage resulting from the initial and secondary injury, irritation of nerve endings from the chemicals released by the inflammatory response, and the effects of low levels of oxygen. Pain leads to a guarding response in nearby muscles, causing a muscle spasm that contributes to a lack of function of the injured body part. Dysfunction can also be caused by a large amount of swelling physically restricting or blocking joint movement.
It is important to note that there is a difference between inflammation and infection. Infections often cause inflammation so the signs and symptoms can be difficult to differentiate as infections often have pain, redness, heat, swelling, and (sometimes) dysfunction. However, infections also tend to produce red streaks coming out from the infected area, pus or other discharge from an open wound, and a fever.
Inflammation is to be expected after an injury (especially an acute one), but infections are a potential cause for concern. If you think you might have an infection, please see a medical professional for proper evaluation and care.
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