Chronic swelling of the leg and stasis ulcer.

Lymphatic fluid Swelling of the leg is a condition often seen in general practice. Most commonly it develops secondarily to a local abnormality in the venous or lymphatic system, but systemic abnormalities such as cardiac or renal failure or myxoedema should not be overlooked. By definition oedema is a pathological accumulation offluid in the interstitial tissues. Physiologists divide the body water into intracellular and extracellular compartments, extracellular compartments consisting of the vascular circulation, lymphatic circulation, and interstitial "fluid." The interstitial fluid is a thin layer ofgel, a colloidal system in which particles of solid are dispersed in a liquid. The interstitial compartment has a capacity to imbibe water but any such tendency is opposed by the osmotic pressure of the plasma, drawing water into the capillaries. The viability of cells is maintained by the continuously occurring transit ofplasma fluid into the interstitial spaces (outward filtration) and back again (inward filtration). This transcapillary fluid exchange is in perfect balance under normal conditions. If this balance is disturbed the sol phase of the colloid increases its volume and oedema arises.