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Inflammation and Events of acute inflammation



Inflammation is a process by which the body's white blood cells and substances they produce protect us from infection with foreign organisms, such as bacteria and viruses. However, in some diseases, like arthritis, the body's defense system -- the immune system -- triggers an inflammatory response when there are no foreign invaders to fight off
Inflammation is a process by which the body's white blood cells and substances they produce protect us from infection with foreign organisms, such as bacteria and viruses

Events of acute inflammation:

Acute inflammation is categorized into an early vascular and a late cellular responses.

1) The Vascular response has the following steps:

a) Immediate (momentary) vasoconstriction in seconds due to neurogenic or chemical stimuli.
b) Vasodilatation of arterioles and venules resulting in increased blood flow.
c) After the phase of increased blood flow there is a slowing of blood flow & stasis dueto increased vascular permeability that is most remarkably seen in the post-capillaryvenules. 




The increased vascular permeability oozes protein-rich fluid into extravascular tissues. Due to this, the already dilated blood vessels are now packed withred blood cells resulting in stasis. The protein-rich fluid which is now found in the extravascular space is called exudate. The presence of the exudates clinically appears as swelling. Chemical mediators mediate the vascular events of acute inflammation.

2) Cellular response

The cellular response has the following stages:
A. Migration, rolling, pavementing, & adhesion of leukocytes
B. Transmigration of leukocytes
C. Chemotaxis
D. Phagocytosis
Normally blood cells particularly erythrocytes in venules are confined to the central(axial) zone and plasma assumes the peripheral zone. As a result of increase cardiovascular permeability (See vascular events above), more and more neutrophils accumulate along the endothelial surfaces (peripheral zone).

A) Migration, rolling, pavementing, and adhesion of leukocytes

Migration is a peripheral positioning of white cells along the endothelial cells.
Subsequently, rows of leukocytes tumble slowly along the endothelium in a process known as rolling. In time, the endothelium can be virtually lined by white cells. 

This appearance is called pavementing. Thereafter, the binding of leukocytes with endothelial cells is facilitated by cell-adhesion molecules such as selectins, immunoglobulins, integrins, etc which result in adhesion of leukocytes with the endothelium.

B). Transmigration of leukocytes

Leukocytes escape from venules and small veins but only occasionally from capillaries. The movement of leukocytes by extending pseudopodia through the vascular wall occurs by a process called diapedesis. The most important mechanism of leukocyte emigration is via widening of interendothelial junctions after endothelial cells contractions. The basement membraneis disrupted and resealed thereafter immediately.

C). Chemotaxis:

A unidirectional attraction of leukocytes from vascular channels towards the site of inflammation within the tissue space guided by chemical gradients (including bacteria and cellular debris) is called chemotaxis. The most important chemotactic factors for neutrophils are components of thecomplement system (C5a), bacterial and mitochondrial products of arachidonicacid metabolism such as leukotriene B4 and cytokines (IL-8). 




All granulocytes, monocytes and to lesser extent lymphocytes respond to chemotactic stimuli.
How do leukocytes "see" or "smell" the chemotactic agent. This is because receptors on cell membrane of the leukocytes react with the chemo-attractants resulting in the activation of  phospholipase C that ultimately leads to release of cytocolic calcium ions and these ions trigger cell movement towards the stimulus.

D) Phagocytosis

Phagocytosis is the process of engulfment and internalization by specialized cellsof particulate material, which includes invading microorganisms, damaged cells,and tissue debris.
These phagocytic cells include polymorphonuclear leukocytes (particularly neutrophiles), monocytes and tissue macrophages.
Inflammation and Events of acute inflammation  Inflammation and Events of acute inflammation Reviewed by gafacom on September 11, 2019 Rating: 5

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