Acute Inflammation I: Inflammatory Response

Acute inflammation is triggered by infection, trauma, or chemical injury that causes tissue damage. The body detects harmful stimuli through resident immune cells like mast cells, macrophages, and dendritic cells, which recognize pathogen-associated and damage-associated molecular patterns via pattern-recognition receptors. This recognition activates the inflammatory cascade.

Activated immune cells release inflammatory mediators such as histamine and prostaglandins, which cause vasodilation and increased blood flow to the injured site, producing erythema and heat. Simultaneously, increased vascular permeability allows fluid to move into surrounding tissue, causing edema. These mediators also sensitize local nerves, generating pain.

Cytokines such as TNF and IL-1 activate the endothelium to express selectins and adhesion molecules on blood vessel walls. These molecules enable leukocytes to roll along the vessel surface, adhere firmly, and transmigrate through the endothelium into inflamed tissue via diapedesis, facilitating immune cell delivery to the injury site.

Acute inflammation is a short-term response that lasts from minutes to several days. This tightly regulated process is designed to eliminate harmful agents and initiate tissue repair. Once pathogens are cleared and debris is removed, the inflammatory response resolves and healing begins.

Leukocytes, particularly neutrophils, perform critical effector functions including phagocytosis of pathogens, release of antimicrobial enzymes, and clearance of necrotic debris. These actions eliminate harmful agents and remove damaged tissue, contributing to resolution of inflammation and promotion of tissue repair and healing.

Vasodilation of local arterioles increases blood flow to the injured area, delivering immune cells and nutrients while producing erythema and heat. Reduced flow velocity due to plasma leakage into tissue facilitates firm adhesion and transmigration of leukocytes across the endothelium, enabling immune cells to reach the inflammation site.

Once leukocytes eliminate pathogens and clear debris, inflammation reduces and tissue repair is promoted. Understanding how acute inflammation progresses to local and systemic effects helps explain the transition from the acute phase to healing. Students can explore acute inflammation iii local and systemic effects for comprehensive coverage of inflammation's broader impact.