N3 Anatomy and Physiology (1st Sem AY 2022-2023)

Inflammation is a nonspecific, defensive response of the body to tissue damage caused by pathogens, abrasions, chemical irritations, and extreme temperatures. It is characterized by redness, pain, heat, and swelling and has three basic stages: (1) vasodilation and increased permeability of blood vessels, (2) emigration (movement) of phagocytes from the blood into the interstitial fluid, and, ultimately, (3) tissue repair.

Vasodilation is the increase in the diameter of arterioles and increased permeability of capillaries which allows more blood to flow through the damaged area. This produces three of the signs of inflammation: heat, redness, and swelling.

After an hour, phagocytes appear on the scene. As large amounts of blood accumulate, neutrophils begin to stick to the inner surface of the endothelium (lining) of blood vessels and squeeze through the wall of the blood vessel to reach the damaged area in a process called emigration.

As the inflammatory response continues, monocytes follow the neutrophils into the infected area which then transform into wandering macrophages. Eventually, a pocket of dead phagocytes and damaged tissue forms; this collection of dead cells and fluid is called pus. Pus formation occurs in most inflammatory responses and usually continues until the infection subsides. 

Innate (nonspecific) immunity is the defense system with which you were born and includes the external physical and chemical barriers provided by the skin and mucous membranes (first line of defense). It also includes various internal defenses, such as antimicrobial substances, natural killer cells, phagocytes, inflammation, and fever (second line of defense)