Factors of edema development
Causes of extracellular edema. Factors leading to edema
Accumulation of liquid in extracellular space occurs whendifferent states. Edema occurs due to increased filtration in the capillary or as a result of impaired lymph flow, which facilitates the return of fluid from the intercellular space to the blood. The following is a rather incomplete list of the causes of extracellular edema, the development of which is due to these two mechanisms.
I. Increase in pressure in capillaries
A. Increased retention of sodium and water by the kidneys
1. Acute or chronic renal failure
2. Excess secretion of mineralocorti-coids
B. High venous pressure and narrowing of venous vessels
1. Heart failure
2. Violation of the permeability of veins
3. Violation of the venous pump
a) muscle paralysis
b) Immobilization of body parts
c) failure of the veins valves
B. Decrease in vascular resistance
1. Overheating of the body
2. Reducing the tone of the sympathetic department of the autonomic nervous system
3. Use of vasodilator drugs
II. Reduction of protein content in plasma
A. Loss of protein in the urine (nephrotic syndrome)
B. Loss of protein through damaged skin
B. Disturbance of protein synthesis
1. Diseases of the liver (eg, cirrhosis)
2. Severe eating disorder or protein deficiency in food
III. Increase in permeability of capillaries
A. Immune reactions accompanied by the release of histamine or mediators of the immune system
B. Bacterial infections
G. Avitaminosis, in particular vitamin C. D. Prolonged ischemia E. Burns
IV. Impaired lymph drainage
A. Oncological diseases
B. Parasitic infection (eg, filariasis)
B. Surgical interventions
Atresia or congenital pathology of lymphatic vessels
Edema caused by heart failure. One of the most frequent and dangerous causesedema is a heart failure, in which the heart is not able to normally pump the blood flowing from the veins into the arteries. Venous pressure increases, and there is an increase in filtration in the capillaries. In addition, there is a tendency to lower blood pressure, which leads to a decrease in the release of salt and water by the kidneys and in turn increases the blood volume and leads to a further increase in hydrostatic pressure in the capillaries, further contributing to the development of edema. Reduction of blood flow in the kidneys also increases the secretion of renin, leading to the formation of angiotensin II, which stimulates the secretion of aldosterone. Both of these factors cause an additional delay in water and salt by the kidneys. Thus, if we do not take measures to treat heart failure, a combination of all these factors will lead to the development of generalized extracellular edema.
In patients with left ventricular failure without significant lesions of the right side of the heartthe flow of blood to the lungs is not disturbed, however, outflow through the pulmonary veins is difficult due to the pronounced weakness of the left half of the heart. Consequently, the pressure in the vessels of the lungs, including the capillaries, is significantly higher than normal, causing a life threatening condition - pulmonary edema, which is able to progress rapidly and, in the absence of treatment, lead to accumulation of fluid in the lungs and death within a few hours.
Edema. caused by a decrease in the release of water and saltkidneys. As noted earlier, most of the NaCl that enters the bloodstream remains in the extracellular fluid, only a small amount enters the cell, so in renal disease, when salt and water are disrupted, they are added in large quantities to the extracellular fluid. Most of the water and salt enters the intercellular fluid, but a small amount remains in the blood. The main results of the changes are: (1) a generalized increase in the volume of extracellular fluid (extracellular edema); (2) increased pressure due to increased blood volume. For example, in children with acute glomerulonephritis (kidneys due to the inflammatory process in the renal glomeruli are not able to filter the required amount of fluid), significant extracellular edema is noted in all areas of the body, and also usually associated severe hypertension.
Edema. caused by a decrease in protein concentration in the plasma. Decrease in protein concentration in plasma due to both a violation of its synthesis in sufficient quantities and leakage of protein from the plasma leads to a reduction in oncotic pressure, which in turn increases the filtration of liquid in the capillaries, leading to extracellular edema.
One of the most important reasons decrease in protein in plasma is the loss of protein in the urine with somekidney diseases called nephrotic syndrome. With various kidney diseases, the kidney glomeruli are damaged, and their membranes become permeable to plasma proteins, which often leads to the appearance of a large amount of protein in the urine. When the losses begin to exceed the amount of protein synthesized by the body, its concentration in the plasma decreases. Significant generalized edema is observed with a protein concentration in the plasma below 2.5 g / dL.
Cirrhosis of the liver - another condition that also causesdecrease in protein concentration in plasma. The term "cirrhosis" means the proliferation of a large amount of fibrous tissue in the liver parenchyma. As a result of cirrhosis, the ability of hepatocytes to synthesize a sufficient number of proteins entering the plasma decreases, which leads to a decrease in oncotic pressure and the development of generalized edema.
Other mechanism of edema in cirrhosis sometimes a mechanical narrowing of the lumenvessels of the portal vein system that drain blood through the liver tissue and discharge into the systemic bloodstream. The obstruction of the venous outflow increases the hydrostatic pressure in the abdominal capillaries, leading to even more filtration of the plasma in the capillaries.
The combined effect a decrease in plasma protein concentration and a high pressure in the capillaries of the portal vein system leads to the transudation of large volumes of fluid and protein in the abdominal cavity - ascites.