Under normal conditions, the dynamics that drive fluid flow inside and outside the capillaries are influenced by the hydrostatic pressure inside and outside the capillaries, the plasma colloid osmotic pressure, and the reflux of lymphatic fluid. When the total intracapillary pressure is greater than the total intertissue fluid pressure, the intravascular fluid is transferred to the intertissue fluid. When it returns to the circulation across the capillaries and lymphatic circuits, it causes excess interstitial fluid to form edema. The factors that lead to the development of edema include: 1) increased hydrostatic capture in capillaries; 2) decreased capillary colloid osmotic pressure; 3) increased interstitial fluid colloid osmotic pressure; 4) decreased interstitial fluid hydrostatic capture; 5) increased capillary permeability; 6) lymphatic vessel obstruction. A variety of diseases can lead to changes in the above factors and result in edema. Many glomerular diseases can also lead to edema, called nephrogenic edema. The mechanisms of nephrogenic edema are: 1) decreased glomerular filtration rate and increased hydrostatic pressure in the row of capillaries due to water and sodium retention; 2) large amount of protein loss, decreased albumin in plasma, and decreased plasma colloid osmotic pressure; 3) increased capillary permeability throughout the body due to inflammation. All of these factors can cause edema.