Acute Inflammation: Mediators and Definitions

Acute Inflammation

• Acute inflammation is a reaction of vascularized living tissues, characterized by the movement of fluid and leukocytes from blood to tissue.
• The process involves oedema, an accumulation of fluid extra-vascularly.
• Exudate is oedema with high protein content.
• Pus is inflamed exudate with dead neutrophils, debris, microorganisms, protein, and lipid.
• Suppuration is the formation of pus.

Purpose of Inflammation

• Inflammation is a defense against microorganisms.
• It eliminates damaged cells and inanimate foreign particles.
• It initiates the healing process.

Characteristics of Acute Inflammation

• Acute inflammation has a rapid onset.
• It is short-lived.

Complications of Acute Inflammation

• Appendicitis
• Meningitis

Chronic Inflammation

• Tuberculosis
• Arthritis
• Initiation of cancer

Mediators of Inflammation

Neutrophils

• Kill microorganisms
• Help endothelial cells regulate the movement of blood to tissues
• Express adhesion molecules

Macrophages

• Degrade fibrin and debris
• Kill microorganisms
• Secrete cytokines

Fibroblasts

• Secrete collagen

Cardinal Signs of Inflammation

• Redness
• Heat
• Swelling (due to fluid accumulation)
• Pain or sensitivity to heat

Hyperaemia and Exudation

• Hyperaemia is an increase in blood flow through tissues due to vasodilation and the opening of dormant capillaries.
• Exudation is an increase in vascular permeability to proteins, leading to congested vessels and swelling accompanied by neutrophils.

Inflammation

• Inflammation is the reaction of vascularised living tissues to local injury or infection, characterised by the movement of fluid and leukocytes from the blood into the affected tissue.

Roles of the Inflammatory Response

• Defence against micro-organisms
• Elimination of damaged cells, inanimate foreign particles, or antigens
• Initiation of the healing process

Types of Inflammation

• Acute Inflammation: a rapid onset, relatively short-lived, stereotypic response to injury or infection, characterised by the movement of fluid and neutrophils out of the blood and into the affected tissue
• Chronic Inflammation: a prolonged response to injury or infection, starts later, lasts longer

Key Points to Remember

• An acute response does not necessarily evolve into a chronic response
• The histological events evolve faster than the clinical picture

Importance of Inflammation

• Positive roles: host defence against micro-organisms, initiating adaptive immune response, initiating tissue healing mechanisms
• Deleterious effects: acute inflammation (e.g. appendicitis, meningitis), chronic inflammation (e.g. tuberculosis, arthritis, tissue destruction)

Cell Types Involved in Inflammation

• Neutrophils: kill micro-organisms
• Endothelial cells: regulate movement of protein from blood into the tissues, express adhesion molecules
• Macrophages: adhere, penetrate, degrade fibrin and debris, kill micro-organisms, secrete regulatory molecules called cytokines
• Fibroblasts: secrete collagen

The Acute Inflammatory Response

• Stereotypic response to injury or infection
• Dislocations, sunburn, muscle tears, insect bites, etc.

The "Cardinal Signs" of Inflammation

• Redness: increased blood flow ("hyperaemia" or "erythema")
• Heat: increased blood flow ("hyperaemia" or "erythema")
• Swelling: fluid movement from blood into tissue ("exudation")
• Pain: increased sensitivity of pain receptors ("hyperalgesia")