EDEMA CAUSES, TYPES & PATHOGENESIS
The Greek word oidema basically means swelling. It is generally an abnormal and excessive accumulation of “free fluid” in interstitial spaces & serous cavity. Edema causes are given following.
EDEMA CAUSES & PATHOGENESIS:
It is basically caused by mechanisms that interfere with the normal fluid balance of plasma, interstitial fluid, and lymph flow.
The following mechanisms may operate alone or in combination to produce edema:
- Firstly Decreased plasma oncotic pressure
- Increased capillary hydrostatic pressure
- Lastly, Increased capillary permeability
- Lymphatic obstruction
- Tissue factors
- oncotic pressure of interstitial fluid increased
- decreased tissue tension
- And lastly Sodium and water retention.
TYPES OF EDEMA:
The edema generally may be of 2 main types:
1. Localised. It is type which is limited to an organ or limb e.g. lymphatic oedema, inflammatory oedema, allergic oedema.
2. Generalised (anasarca or dropsy). This type is when there is systemic in distribution, particularly seen in the subcutaneous tissues e.g. renal oedema, cardiac oedema, nutritional Oedema, Hepatic oedema.
Besides, there are some other special forms of oedema (e.g. pulmonary, cerebal edema)
Generalized edema occurs in certain diseases of renal origin such as in nephrotic syndrome, some types of glomerulonephritis, and renal failure due to acute tubular injury.
A. Normal fluid exchange at the alveolocapillary membrane (i.e. capillary endothelium and alveolar epithelium). B. Pulmonary edema via elevated pulmonary hydrostatic pressure. C. Pulmonary edema via increased vascular permeability.
CEREBRAL EDEMA CAUSES:
Cerebral edema or swelling of the brain is the most threatening e.g. of edema. Therefore, The mechanism of fluid exchange in brain differs from other place in the body. Because there are no lymphatic drainage in brain. But, the function of fluid-electrolyte exchange is performed by blood-brain barrier located at endothelial cells of the capillaries.
Cerebral edema can be of 3 types i.e.:
- VASOGENIC OEDEMA. This is the basically most common type and corresponds to oedema elsewhere resulting from increased filtration pressure or increased capillary permeability. Vasogenic oedema is generally shown around cerebral contusions, infarctions, brain abscess and some tumours.
- CYTOTOXIC OEDEMA. In this type, the blood-brain barrier is moreover intact and the fluid accumulation is intracellular. The underlying mechanism is disturbance in the cellular osmoregulation. It also occurs as in some metabolic derangements, acute hypoxia and with some toxic chemicals.
- INTERSTITIAL OEDEMA. This type of cerebral oedema basically occurs when excessive fluid crosses the ependymal lining of ventricles and get collected in the periventricular white matter. This mechanism is generally responsible for oedema in noncommunicating hydrocephalus.
i) There is generally hypoproteinaemia. It is because of impaired synthesis of proteins by the diseased liver.
ii) Due to portal hypertension, there is increase venous pressure in abdomen. and therfore raised hydrostatic pressure.
iii) Failure of not activation of aldosterone in diseased liver. So hyperaldosteronism is caused.
iv) Secondary stimulation of the renin-angiotensin mechanism basically promoting sodium and water retention.
Edema is generally due to nutritional deficiency of proteins (kwashiorkor, prolonged starvation, famine, fasting), vitamins (beri-beri due to vitamin B1 deficiency) and chronic alcoholism occurs on legs but sometimes maybe more generalized. The main contributing factors are basically hypoproteinaemia and metabolic abnormalities related to sodium-water retention.