Why does Drop in Osmotic Pressure Cause Swelling in Nephrotic Syndrome

There are tiny blood vessels in the kidneys that filter waste and excess water from the blood stream. When these filters are damaged, a person will get Nephrotic Syndrome. The most common early symptom of this disorder, in both children and adults, is swelling in the tissues around the eyes or in the ankles or feet due to drop in osmotic pressure. The following gives detailed introduction.

Colloid Osmotic Pressure

It can also be referred to as oncotic pressure, which is a measurement of pressure exerted within the cardiovascular system by proteins found in blood plasma. Maintaining the proper levels osmotic pressure ensures that the body tissues maintain the proper levels of liquid and that too much liquid doesn't escape from the capillaries.

Normally, colloid osmotic pressure tends to cause fluid to be drawn into the capillaries. Variations in this pressure can lead to build up of fluid in the tissues, a condition called edema, or swelling.
Swelling due to Drop of Osmotic Pressure in NS

Individuals with NS suffer from large quantity of Urine Protein. Massive proteins will get released into the urine, leading to reduced amount of plasma colloid osmotic pressure. If this happens, the normal exchange of body fluid is disturbed and cannot keep balance any more. Water in blood vessels will transfer toward tissue fluid, resulting in swelling.

Besides, another cause of edema in NS is also associated with low blood protein concentration.
Water in the blood transfers toward interstitial tissue, leading to low effective blood volume. This in turn gives rise to the production of Anti-diuretic Hormone (ADH). Renal tubules will reabsorb more water and sodium, resulting in more water retention. This condition will aggravate the swelling in NS.