Most characteristic feature of acute inflammation:

The main vascular reactions of acute inflammation are increased blood flow secondary to vasodilation and increased vascular permeability, both designed to bring blood cells and proteins to sites of infection or injury.Changes in Vascular Caliber and FlowAfter transient vasoconstriction (lasting only for seconds), aeriolar vasodilation occursThe microvasculature becomes more permeable, and protein-rich fluid moves into the extravascular tissuesAs stasis develops, leukocytes (principally neutrophils) begin to accumulate along the vascular endothelial surface--a process called marginationIncreased Vascular PermeabilitySeveral mechanisms may contribute to increased vascular permeability in acute inflammatory reactions areEndothelial cell contraction leading to intercellular gaps in postcapillary venules is the most common cause of increased vascular permeability.Endothelial injury results in vascular leakage by causing endothelial cell necrosis and detachmentIncreased transcytosis of proteins by way of an intracellular vesicular pathway augments venular permeabilityLeakage from new blood vessels.( Robbins Basic Pathology, 9th edition, page 33 )