Proteinuria and hematuria are two main symptoms of various kinds of kidney diseases, but why these symptoms happen? Most of patients just been told that their renal cells are damaged, or their kidneys are damaged, but this is not clear, actually the occurrence of Proteinuria and hematuria have something to do with glomerular filtration membrane.
The permeability of glomerular filtration membrane can be measured by molecular weight that allowed passing. Small molecules in blood are easy to get through various pores on filtration membrane; but for large charged molecules, such as plasma albumin whose molecular weight is 69000 is hard to get through. For the molecules whose molecular weight is higher than 69000, they could never get through filtration membrane.
On the other hand, generally the haemoglobin whose molecular weight is 64000 can pass filtration membrane, but after combining with globin, this new complex can not pass any more. When serious hemolysis occurs, the volume of haemoglobin will more than the volume of globin, under this situation, the haemoglobin which can not combined with globin will be discharged by urine. That’s why hemoglobinuria occurs.
Generally, the permeability of glomerular filtration membrane is relatively stable, the composition of urine will change only under the circumstance of Pathological changes. For example, the proteinuria will occur under circumstance of glomerulonephritis or anoxia. The recent study shows that the appearance of proteinuria is caused by pathological changes which can lead to the disappear or decrease of sialoprotein on filtration membrane, then the electric charge mutual repulsion will be weak, finally it will be much easy to leak albumin. And when this kind of pathological changes cause the damage of filtration membrane, it is also possible for erythrocyte to leak through urine.