Swelling of the feet is also known as pedal oedema this occurs primarily in kidney disease because of retention of fluid. The kidney is responsible for several functions. When the ability of the kidney to remove fluid from the body is decreased fluid is retained. The increased fluids within the blood vessels eventually leak through the walls of the smallest capillaries and enter the soft and sponge like tissues beneath the skin known as the subcutaneous tissue giving rise to the symptom of swelling. Due to the fact that fluid always settles in a dependent position the swelling is usually observed to be in the lower limbs if the patient is standing or around the waste and back if sitting or lying down. Very severe cases of swelling may be seen with swelling of the entire body a situation known as anasarca. This symptom usually occurs in very severe kidney disease or in cases where there is retention of fluid due to losses of protein in the urine.
It is difficult to conceptualize at first that loss of protein in the urine may lead to retention of fluid within the body. However one of the roles of protein is to provide one of the main constituents of blood. This constituent is known as albumin the same albumin that is found in egg white. This protein attracts fluid to itself therefore the more albumin you have in your blood stream the more fluid will want to be attracted to and remain within the blood vessel. If the albumin levels within the blood are low then the fluid will be less attracted to remain within the blood vessels and instead will leak wherever there is a pressure difference such as in the loose tissues beneath the skin where there is relatively low pressure and a willingness to expand to accommodate fluid.
Nephrotic syndrome is a type of kidney disease where there are large quantities of protein leaking into the urine. The first symptom of kidney disease noted in these patients is usually swelling of the feet.
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