Hydrostatic & colloidal osmotic pressure: relationship?

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Hydrostatic pressure is a measure of the effort a fluid, such as water, exerts while it is at rest. There are two influencing factors: local gravity and liquid density. Colloidal osmotic pressure (COP) is the amount of strain of blood plasma proteins that have the ability to attract water into the circulatory system. Plasma proteins within the capillaries maintain a high pressure balance to prevent fluids from flowing out of the capillaries, normally. If there is a loss of colloidal osmotic pressure, this balance can be disturbed, allowing fluids to cross membrane barriers into tissues and causing a fluid buildup known as edema.

In cancer studies to determine whether COP and hydrostatic pressure show any difference between cancerous tissue and fluids and normal tissue and fluids, breast cancers showed a marked drop in hydrostatic pressure and an increase in colloidal osmotic pressure, causing loss of tumor vessels. Studies of three other types of tumors have shown a difference between pressure readings in tumor tissue compared to pressure readings in normal tissue. The differences weren’t as marked, however, as in breast cancer tumors. Loss of cell membrane integrity and tissue inflammation within tumors are thought to cause elevated COP readings.

Fluid balances usually equalize in normal blood vessels and surrounding interstitial tissue; however, because high blood sodium helps proteins draw water into the blood supply, it can lead to a saturated vessel condition known as hypervolemia and a subsequent dehydration of surrounding tissues. The opposite is true when sodium levels drop and hydrostatic pressures hold fluids in the tissues. Since hydrostatic pressure is a mechanical force, when there is a drop in blood pressure, circulatory shock will cause mild symptoms of tachycardia and mild peripheral vasoconstriction of vessels, or severe symptoms including systolic rates less than 60, marked pallor, and mental stupor. States of neurogenic, anaphylactic, or septic shock show marked increases and decreases in hydrostatic pressures and colloid osmotic pressures and show signs of hypervolemia or hypovolemia.

A condition known as ascites is an abnormal accumulation of fluid in the tissues of the abdominal area. Diseases such as cirrhosis and high blood pressure cause ascites and are usually treated with low-sodium diets and diuretics; however, some patients require more relief. A treatment known as transjugular intrahepatic portosystemic shunt (TIPS) has in recent years begun to provide significant improvements in 50-70% of cases, with few complications. These successes show an increase in colloidal osmotic pressure and a balance of the decrease in hydrostatic pressure, inhibiting further loss of water from blood vessels.

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