Question

When an animal is wounded, its overall blood pressure increases, but the area in the vicinity of the wound swells as a result of vasodilation. Why?

Answer 1

Hint: Inflammation is the standard initial response of the body to the injury. It does not matter what kind of injury it is, all injuries lead to the same sequence of physiological events.

Complete answer:
Let's try to understand what causes swelling after an injury. Following an injury, the area becomes red, warm, and painful and begins to swell. This swelling in technical terms is called trauma which is a result of ‘acute inflammation’, which is a triggered response by damaged tissues. The swelling occurs due to the accumulation of the body fluid and the white blood cells in the injured area. The injured area mostly releases histamine which acts as a vasodilator.
Now let's study in detail the sequence of events that follow an injury.
Heat, pain, redness, swelling, and loss of function are the five classical signs of inflammation. In case of injury, the first healing stage is characterized by the change in the blood flow in the damaged area. The blood vessels of that area eventually dilate and increase blood flow into the tissues, creating redness. This is followed by an increase in blood vessel permeability, allowing food proteins and white blood cells to migrate from the circulation to the site of tissue damage. This input of fluid cells and other substances to the injured sites is what produces the swelling, which sometimes restricts the movement of the affected part. The swelling, heat, and redness of the traumatized tissue area are reduced by the action of WBCs, which is ‘phagocytosis’. This results in the cleaning up of the damaged tissue.

Note: It is useful to differentiate inflammation and infection, these are not synonyms. ‘Infection’ describes the interaction between the action of the foreign microbe and the body's reaction with the inflammatory response they are collectively talked about in infection, while inflammation just describes the immunovascular response of the body irrespective of the cause.