Edema will occur in specific organs as part of inflammation, as in pharyngitis, tendonitis or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms.
Examples of edema in specific organs:
- Cerebral edema is extracellular fluid accumulation in the brain. It can occur in toxic or abnormal metabolic states and conditions such as systemic lupus. It causes drowsiness or loss of consciousness.
- Pulmonary edema occurs when the pressure in blood vessels in the lung is raised because of obstruction to removal of blood via the pulmonary veins. This is usually due to failure of the left ventricle of the heart. It can also occur in altitude sickness or on inhalation of toxic chemicals. Pulmonary edema produces shortness of breath. Pleural effusions may occur when fluid also accumulates in the pleural cavity.
- Edema may also be found in the cornea of the eye with glaucoma, severe conjunctivitis or keratitis or after surgery. It may produce coloured haloes around bright lights.
- Edema surrounding the eyes is called ''periorbital edema'' or eye puffiness. The periorbital tissues are most noticeably swollen immediately after waking, perhaps due to the gravitational redistribution of fluid in the horizontal position.
- Common appearances of cutaneous edema are observed with mosquito bites, spider bites, bee stings (wheal and flare), and skin contact with certain plants such as Poison Ivy or Western Poison Oak, the latter of which are termed ''contact dermatitis''.
- Another cutaneous form of edema is myxedema, which is caused by increased deposition of connective tissue. In myxedema (and a variety of other rarer conditions) edema is due to an increased tendency of the tissue to hold water within its extracellular space. In myxedema this is because of an increase in hydrophilic carbohydrate-rich molecules (perhaps mostly hyaluronan) deposited in the tissue matrix. Edema forms more easily in dependent areas in the elderly (sitting in chairs at home or on aeroplanes) and this is not well understood. Estrogens alter body weight in part through changes in tissue water content. There may be a variety of poorly understood situations in which transfer of water from tissue matrix to lymphatics is impaired because of changes in the hydrophilicity of the tissue or failure of the 'wicking' function of terminal lymphatic capillaries.
- In the case of human feet, the Starling forces are always a long way out of balance, because the variation in hydrostatic pressure in the vessels in the feet as compared to the face is about a metre of water. In severe heart failure the change in central venous pressure is tiny in comparison and cannot explain why edema of the feet develops simply through an effect on capillary leakage. Three other factors may be involved. If the central venous pressure rises to equal that of the thoracic lymph duct then clearance of fluid from the tissue will be impeded (see below). That is to say the edema may actually be caused by a change in output of fluid from the tissue, as much as input to the tissue. Secondly, severe heart failure is one of the most exhausting conditions there is. The sufferers tend to spend what little effort they can make trying to breathe with edematous lungs. They tend to sit up to make breathing easier and their feet hang immobile on the floor. Immobility is perhaps the commonest of all causes of edema, because clearance of fluid via the lymphatics needs muscle action. Thirdly, in severe heart failure endocrine and neural changes alter the way tissues are perfused in ways that are not fully understood.
- In lymphedema abnormal removal of interstitial fluid is caused by failure of the lymphatic system. This may be due to obstruction from, 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). It is most commonly due to a failure of the pumping action of muscles due to immobility, most strikingly in conditions such as multiple sclerosis, or paraplegia. Lymphatic return of fluid is also dependent on a pumping action of structures known as lymph hearts. It has been suggested that the edema that occurs in some people following use of aspirin-like cyclo-oxygenase inhibitors such as ibuprofen or indomethacin may be due to inhibition of lymph heart action.
Further Reading
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