Acute Inflammation

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Acute Inflammation
The survival of all organisms requires that they eliminate foreign invaders, such as infectious pathogens, and damaged tissues. These functions are mediated by a complex host response called inflammation. Definition of inflammation

Inflammation is fundamentally a protective response, the ultimate goal of which is to rid the organism of both the initial cause of cell injury (e.g., microbes, toxins) and the consequences of such injury (e.g., necrotic cells and tissues) The process of inflammation is usually described by the suffix “itis”

[The components of the inflammatory reaction that destroy and eliminate microbes and dead tissues are capable of also injuring normal tissues. Therefore, injury may accompany entirely normal, beneficial inflammatory reactions, and the pathology may even become the dominant feature if the reaction is very strong (e.g., when the infection is severe), prolonged (e.g., when the eliciting agent resists eradication), or inappropriate (e.g., when it is directed against self-antigens in autoimmune diseases. or against usually harmless environmental antigens in allergic disorders). Some of the most vexing diseases of humans are disorders in which the pathophysiologic basis is inappropriate, often chronic, inflammation. This is why the process of inflammation is fundamental to virtually all of clinical medicine.]

Acute inflammatory reactions are triggered by a variety of stimuli: • Infections (bacterial, viral, parasitic) and microbial toxins • Trauma (blunt and penetrating)
• Physical and chemical agents (thermal injury, e.g., burns or frostbite; irradiation; some environmental chemicals) • Tissue necrosis (from any cause)
• Foreign bodies (splinters, dirt, sutures)
• Immune reactions (also called hypersensitivity reactions

Cardinal signs of inflammation
Celsus, a Roman writer of the first century AD, first listed the four cardinal signs of inflammation Rubor, Calor, Dolor, Tumour & Functio laesa Rubor- redness
Calor – heat (Increased blood flow can be visualized as redness (rubor) and felt as heat (calor) Tumor – swelling (due to edema)
Dolor - pain
The fourth cardinal sign of inflammation is pain (dolor). This is the result of increased pressure in the interstitium due to edema. Pain fibers are stimulated through pressure receptors but also may be stimulated by the direct effects of bradykinin, a plasma protease end product of the kinin system A fifth clinical sign, Functio laesa- loss of function was later added by Virchow.

Acute inflammation has two major components:
Vascular events
The 2 major vascular changes are:
(1) Alterations in vascular caliber that lead to an increase in blood flow (vasodilatation) (2) Structural changes in the microvasculature that permits plasma proteins and leukocytes to leave the circulation (Increased Vascular Permeability) Cellular events

1. Leukocyte extravasation
2. Chemotaxis
3. Phagocytosis
Vascular events
Vascular changes play an important role in acute inflammation. Normally, plasma proteins and circulating cells are sequestered inside the vessels and move in the direction of flow.(laminar flow) In inflammation, the blood vessels undergo a series of changes to maximize the movement of plasma proteins and circulating cells, out of the circulation and into the site of injury. The 2 major vascular changes are:

1.Changes in vascular flow and caliber (vasodilatation)
• Vasodilation is one of the earliest manifestations of acute inflammation. Sometimes, it follows a transient constriction of arterioles, lasting a few seconds. • Vasodilation first involves the arterioles and then results in opening of new capillary beds in the area. Thus comes about increased blood flow, which is the cause of the heat and the redness. • Vasodilation is induced by the action of several mediators, notably histamine and nitric oxide, on vascular smooth...
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