Edema is swelling caused by excess fluid trapped within body tissues. Under normal circumstances the vascular system delivers nutrients to the cells through the capillary beds. Fluid diffuses out of the vessels and into the space between cells following the hydrostatic pressure gradient that exists at the beginning of the capillary beds. Exchange of nutrients and waste occurs between the fluid and the cells. At the far end of the capillary bed, the hydrostatic pressure is lower, reducing the resistance of fluid to reenter the vessels. In addition, osmotic pressure resulting from the prior fluid loss reverses the pressure gradient, drawing fluid back into the vessels. Most of the fluid that leaves vessels in the capillary bed reenters the vessels in this manner. Some of the fluid that is not recovered by the circulatory system passes into the lymphatic system. This system consists of a series of ducts and valves that moves the fluid toward the center of the body and delivers it back to the circulatory system.
When this process is not working properly, it can cause edema, usually in the hands, arms, feet, ankles, and/or legs. In addition to the problems caused by swelling, edema can be a sign of other medical problems. Congestive heart failure is a condition where the ventricle(s) of the heart do not pump blood effectively. This can result in blood accumulation in a patient’s legs, ankles, and feet, causing edema. Kidney damage can reduce the protein concentration in the blood, reducing the osmotic pressure during uptake. Damage to the lymphatic system can also limit the body’s ability to rid itself of excess interstitial fluid.
