Definitions

edema

edema

[ih-dee-muh]
edema, abnormal accumulation of fluid in the body tissues or in the body cavities causing swelling or distention of the affected parts. Edema of the ankles and lower legs (in ambulatory patients) is characteristic of congestive heart failure, but it can accompany other conditions, including obesity, diseased leg veins, kidney disease, cirrhosis of the liver, anemia, and severe malnutrition. Edema is the result of venous ulceration, which is often caused by an increase in tissue pressure (increased fluid within the tissue) because of increased capillary permeability. A failing heart is often accompanied by edema because the blood backs up into the veins, venules, and capillaries, thereby increasing blood pressure. In severe cases of heart failure, the abdomen may fill with fluid; this condition is called ascities. Appendage edema is often treated by bandaging the area to relieve pressure on the skin and decrease venous pressure. More severe cases may require a surgical procedure that diverts the blood flow to healthy veins. The accumulation of fluid within the lungs is a serious complication of cardiac failure, pneumonia, and other disorders. The collection of fluid in the pleural space (within the two-layered membrane surrounding the lungs) can be the symptom of numerous infectious and circulatory disorders. Lymphatic obstructions may result from various surgical procedures or from certain parasitic infections. These blockages cause increased back pressure in the lymph vessels and interfere with movement of fluid from interstitial tissue into venule ends of capillaries. The resulting collection of water within the skull is a serious and usually incurable condition (see hydrocephalus). Since edema is a symptom, the underlying cause must be treated.

Abnormal accumulation of watery fluid in the spaces between connective-tissue cells. Usually a symptom of diseases of the kidneys, heart, veins, or lymphatic system, which affect water balance in the cells, tissues, and blood, edema can be pitting (retaining an imprint when compressed) or nonpitting. Edema may be local (e.g., hives from allergies) or generalized (also called dropsy), sometimes involving body cavities as well as tissues. Treatment must usually focus on the underlying cause.

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Oedema (or Edema in American English), formerly known as dropsy or hydropsy, is the increase of interstitial fluid in any organ — swelling. Generally, the amount of interstitial fluid is determined by the balance of fluid homeostasis, and increased secretion of fluid into the interstitium or impaired removal of this fluid may cause edema.

Edema has five pathophysiologic causes. It can be due to increased hydrostatic pressure, reduced oncotic pressure, lymphatic obstruction, sodium retention, or inflammation.

Mechanism

Generation of interstitial fluid is regulated by the Starling equation of tissue fluid which states that it depends on the balance of osmotic pressure and of hydrostatic pressure which act in opposite directions across the semipermeable capillary walls. Consequently, anything that increases oncotic pressure outside blood vessels (for example, inflammation), or reduces oncotic pressure in the blood (states of low plasma osmolality, for example, cirrhosis) will cause edema. Increased hydrostatic pressure inside the blood vessel (for example, in heart failure) will have the same effect. If the permeability of the capillary walls increases, more fluid will tend to escape out of the capillary, which can happen when there is inflammation.

Abnormal removal of interstitial fluid is caused by obstruction of the lymphatic system. This may be due to, for example, pressure from a cancer or enlarged lymph nodes, destruction of lymph vessels by radiotherapy, or infiltration of the lymphatics by infection (such as elephantiasis).

There are two types: exudate and transudate.

Organ-specific edema

Examples of edema in specific organs:
*Ascites is effectively edema within the peritoneal cavity
*Pleural effusions are effectively edema in the pleural cavity
*Cerebral edema is intracellular or extracellular fluid accumulation in the brain
*Edema may also be found in the eyes after corrective surgery or procedures of that nature.

Causes of edema which are generalized to the whole body can cause edema in multiple organs and peripherally. For example, severe heart failure can cause peripheral edema, pulmonary edema, pleural effusions and ascites.

Common and usually harmless appearances of cutaneous edema are observed with mosquito bites, bee stings (wheal and flare), and skin contact with certain plants (contact dermatitis).

Edema in plants

Edema in plants is the extended swelling in plant organs caused primarily by an excessive accumulation of water. This occurs since the cell walls are composed of flexible cellulose.

References

  • Cho S, Atwood J (2002). "Peripheral oedema". Am J Med 113 (7): 580–6.

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