You have a patient whose renal biopsy revealed significant glomerular sclerosis,

Question

You have a patient whose renal biopsy revealed significant glomerular sclerosis, basement membrane thickening, and podocyte foot process effacement (i.e., foot processes detach from glomerular capillaries). Describe what these renal biopsy results reveal about patient's ability to complete blood filtration. Be sure to discuss the process of filtration, including a description of the normal structure and function of the filtration membrane and resulting net filtration pressures, and discuss resulting changes.

Explanation / Answer

Normal process of filtration: A glomerulas is the network of capillaries surrounded by a cup like sac known as Bowman's capsule. The glomerulas capillaries has the lining of endothelial cells and podocytes. The glomerulas and its surrounding cnsist of renal corpuscle which is basic unit of filtration. Here the blood plasma is filtered through the capillaries. The glomerulus has a basement membrane which is composed mainly of laminins, type IV collagen, agrin and nidogen, which are synthesized and secreted by both endothelial cells and podocytes of the capillary wall. These form a membrane 250–400 nm in thickness, it plays a role in the permeability and selectivity of the filtration barrier to large molecules, such as albumin. There are increased extracellular deposits inside the renal corpuscle occurs in the case of glomerular sclerosis and also the surface area available for filtration decreased. Although the thickening of basement membrane occurs, yet the membranes more leaky. Disruption of the podocyte cytoskeleton, which results in podocyte effacement. The most important effect of these changes in the glomerulus is that they create a leaky filtration membrane, so there is abnormally increased filtration of protein. Proteinuria then causes damage to the renal tubules and further loss of nephrons. Since the surface area available for filtration is decreased the rate of filtration also decreases. In normal condition the basement membrane allows the proper rate of filtration by maintating the filtration pressure through selective permeability but in case of extra thickening of membrane causes leaky membrane leading to change in permeability which causes decrease in filtration presuure and thus no proper formation of urine occurs. These all condition combindingly may cause renal faliure.

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