The glomerulus of the kidneys are the parts that normally filter the blood. They consist of fenestrated (leaky) capillaries, that allows fluid, salts and other small solutes to flow through, but normally not proteins.
In nephrotic syndrome, the glomerulus has been damaged by diabetes, glomerulonephritis or even prolonged hypertension (high blood pressure). This means that small proteins, such as albumin can pass through the kidneys into urine.
Nephrotic syndrome is characterised by proteinuria (detectable protein in the urine), and low albumin levels in blood plasma. As a compensation, the liver begins to make more of all its proteins, and levels of large proteins (such as alpha-2 macroglobulin) increase.
Lack of albumin will cause oedema (swelling), as water moves from the blood into the tissues. Cholesterol levels are also increased, and though the mechanism isn't fully understood, it is thought to be a result of cholesterol processing enzymes being lost into urine.
When treating nephrotic syndrome, if the underlying problem is apparent, (e.g. hypertension, diabetes) then this should be addressed.
Nephrotic syndrome can lead to renal failure.
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