Define inflammation. Explain vascular and cellular events of acuteinflammation.

Inflammation is a biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective response involving immune cells, blood vessels, and molecular mediators, aiming to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, and initiate tissue repair.

Acute inflammation is characterized by two main processes: vascular changes and cellular events.

1. Vascular Events: These events are the initial response to tissue injury. They include changes in vascular flow and caliber, structural changes that allow plasma proteins and leukocytes to leave the circulation, and migration of leukocytes into the injured tissue.

   • Vasodilation: This is the first response, leading to an increase in blood flow, which causes the redness and heat observed in inflammation.

   • Increased Vascular Permeability: This allows protein-rich fluid to move into the tissues, resulting in swelling or edema.

   • Stasis: As fluid leaves the blood vessels, blood flow slows, allowing leukocytes to accumulate along the vessel wall.

2. Cellular Events: These involve the movement of white blood cells from the blood vessels into the tissues to eliminate the cause of the injury.

   • Margination and Rolling: Leukocytes move to the periphery of the blood vessels and start to roll along the vessel wall.

   • Adhesion and Transmigration: Leukocytes adhere to the endothelial cells of the blood vessel wall and then migrate through the wall into the tissue.

   • Chemotaxis: Leukocytes move towards the site of injury in response to chemical signals.

   • Phagocytosis: Leukocytes engulf and digest the harmful stimulus, such as bacteria or dead cells.

These events are tightly regulated to ensure the inflammation resolves once the harmful stimulus is eliminated. However, if these processes are not properly controlled, they can lead to chronic inflammation, which can cause tissue damage.