Accumulation of fluid in the extra cellular space that is rich in proteins and inflammatory cells due to increased vascular permeability

In acute inflammation inflammatory mediators act on blood vessel and increased blood flow to site of inflammation this leads to increased hydrostatic pressure in the blood vessels. Inflammatory mediators act on endothelium and leads to increased vascular permeability by contracting and retracting the endothelium. Direct injury to endothelium also leads to increased vascular permeability. This increase vascular permeability leads to leakage of protein rich fluid in to extracellular space 

Exudate contains all proteins in the plasma which include complements, cytokines, immunoglobulin, and fibrinogen. Exudate rich in inflammatory cells like neutrophils, lymphocyte, and macrophage.

Aim of exudate formation is to bring inflammatory cells and proteins into site of inflammation 

Exudation helps to combats with injuries agent by

Diluting it 

Restriction of spread by forming fibrin mess

Facilitate the phagocytosis by opsonization  with immunoglobulin and complement 

Neutralizing toxins

Disadvantage of exudate formation is pain, swelling and dysfunction of tissue. 

E.g. - 

• Inflammation of brain tissue leads to swelling of brain tissue leading to increase intracranial pressure may result herniation of tonsils
• Pneumonia leads to dysfunction of gas exchange