Edema is a swelling caused by the build-up of abnormally large amounts of fluid accumulating in interstitial tissues, which represents the space surrounding the body's cells and blood vessels. It is a symptom rather than a disease and may be caused by systemic disorders involving different organ systems, or by localized conditions involving the area where the swelling manifests itself. Edema may occur throughout the body as a generalized swelling, or it may affect only a specific part, most often the lower extremities. While edema may be difficult to detect in light cases, larger amounts of accumulated fluid are visible and palpable and may present as either pitting or non-pitting edema. If an indentation is visible for some time following the release of pressure applied to the affected area, the swelling is referred to as pitting edema or soft edema.
The main function of the kidneys is to remove waste products and extra water from the body, which are excreted with the urine. The removal of waste products and water is managed by small structures within the kidneys, called nephrons, which filter these substances from the blood. A number of conditions, such as diabetes, high blood pressure or toxic injury to the kidneys from drugs, may damage the nephrons, resulting in kidney disease. Certain kidney diseases, such as nephrotic syndrome, cause an abnormal loss of certain proteins from the blood into the urine. Water molecules attach themselves to protein; a sufficient concentration of certain proteins in the blood is therefore necessary to maintain fluid balance. With abnormally low protein concentrations in the blood, fluid leaks into the tissues, causing edema.
Chronic Venous Insufficiency
The veins return blood to the heart from all the body's tissues. The venous blood returning from the legs needs to flow upward against the forces of gravity. To maintain a sufficient return of blood back to the heart, the veins in the legs depend on muscle pump activity of the calf muscles and the muscles in the feet. With each contraction of these muscles blood inside the veins is squeezed upward. One-way valves within the veins ensure that the blood flows up, and not back down. Chronic venous insufficiency occurs when these valves become damaged, the veins become dilated or the muscle pump activity becomes insufficient, allowing the blood to leak backward. The excess fluid within these veins causes a pooling effect, forcing fluid to leak into the interstitial tissues of the lower extremities.
Congestive Heart Failure
This is a condition in which the pumping action of the heart is impaired. Various causes, such as impaired blood supply of the heart muscle itself, as in coronary artery disease, high blood pressure or disorders of the heart valves, can be responsible for the weakening of the heart muscle. Over time, the heart is no longer able to keep up with the demands placed on it to pump blood into the arteries of the body systems and to receive blood returning from the body in the veins. This may cause a pooling effect of blood resulting in increased pressure within the veins. High intravenous pressure forces fluid to leak into the interstitial tissues, which causes edema. Various areas of the body, such as the legs and feet, abdomen and organs may be affected by the swelling.