Inflammation and Its Roles

Definition and Roles of Inflammation

• Inflammation is the response of living tissues to an injury, aiming to eliminate or limit the spread of the injurious agent, remove necrotic cells, and prepare the affected tissue for repair.
• Roles of inflammation: isolation and elimination of the injury, destruction of invading organisms and inactivation of toxins, and achieving healing and repair.

Causes of Inflammation

• Biological causes: bacteria, viruses, fungi, and parasites.
• Physical causes: excessive heat or cold, radiation, and electricity.
• Chemical causes: acids, alkalis, organic and inorganic compounds.
• Mechanical causes: wounds, crushing injuries, fractures, and foreign bodies.

Types of Inflammation

• Acute inflammation: rapid onset, short duration, high dose of irritant, and acute inflammatory cells.
• Chronic inflammation: gradual onset, long duration, low dose of irritant, and chronic inflammatory cells.
• Subacute inflammation: grades in-between acute and chronic inflammation.

Case Study

• A 7-year-old boy complains of sore throat, fever, difficulty in swallowing, and swollen tonsils and glands in the neck, indicating inflammation.

Acute Inflammation

• Definition: immediate response of living tissue to an injury, aiming to deliver leukocytes and mediators to the site of injury by the bloodstream.
• Cardinal signs of acute inflammation: redness, hotness, pain, swelling, and loss of function.

Vascular Response

• Transient vasoconstriction: due to direct stimulation of the vascular wall of arterioles.
• Vasodilatation: due to local axon reflex and release of vasodilator substances as histamine.
• Slowing of blood stream: due to vasodilatation, opening of new capillary buds, increased vascular permeability, and increased blood viscosity.

Local Reactions

• Local tissue destruction: maximum at the site of the irritant, depending on its severity.
• Dilatation of lymphatics: lymph flow is increased, allowing drainage of excess extravasated fluid back to blood.

Mechanism of Inflammatory Fluid Exudate

• Increase in capillary hydrostatic pressure due to increased blood flow.
• Increased capillary permeability due to vasodilatation and endothelial injury, and release of histamine.
• Increased osmotic pressure of interstitial tissue due to protein breakdown.

Composition and Functions of Inflammatory Fluid Exudate

• Composition: high protein content, high specific gravity, and turbid and yellowish due to the presence of leukocytes.
• Functions: dilutes toxins, brings fibrinogen, transports antibodies, and helps movement of acute inflammatory cells to the site of the irritant.

Cellular Responses

• Exudation of leukocytes: margination due to stasis, adhering to the inner endothelial wall.
• Phagocytosis: engulfing and destroying foreign particles and bacteria.