The first vascular reaction in inflammation is Vasodilation.
Explanation:
Inflammation is the body's protective response to tissue injury or infection. It
is characterized by the classical signs of redness (rubor), heat (calor),
swelling (tumor), pain (dolor), and loss of function (functio laesa). The
initial vascular changes in the inflammatory process include:
1. Vasoconstriction: This is a temporary response that occurs immediately after
injury to minimize blood loss. However, it is quickly followed by the more
significant and prolonged phase of vasodilation.
2. Vasodilation: This is the first major vascular reaction in the inflammatory
response. Vasodilation occurs due to the release of substances such as
histamine, bradykinins, and prostaglandins from the damaged tissue cells and
mast cells. These substances are known as vasodilators and they cause the smooth
muscles surrounding the blood vessels to relax, leading to an increase in the
diameter of the blood vessels. This results in increased blood flow to the
injured area, which is essential for delivering white blood cells, nutrients,
and oxygen to the site of inflammation. The increased blood flow is what causes
the characteristic redness and heat of an inflamed area.
3. Increased vascular permeability: Although it is not the first vascular
reaction, increased vascular permeability is a critical component of the
inflammatory process. After vasodilation, the endothelial cells that line the
blood vessels become more permeable, allowing plasma and proteins to leak out of
the vessels into the surrounding tissue. This leads to the formation of an
exudate, which is the accumulation of fluid and proteins that makes up the
swelling (edema) seen in inflammation.
4. Marginisation or Pavementing: This is the process where neutrophils (a type
of white blood cell) move along the walls of blood vessels towards the site of
inflammation. It occurs later in the inflammatory response after the initial
vasodilation and increased vascular permeability. These cells then migrate
through the vessel walls into the tissue to combat pathogens and debris.