Filtration OR selective reabsorption by the nephron may not be functioning properly. Improper filtration will lead to proteins getting filtered even though they are not wasted.
After filtration, useful substances such as proteins may not be getting reabsorbed.
Proteinuria, the presence of significant amounts of protein in the urine, typically occurs when there is a disruption in the normal filtration and reabsorption processes that take place in the nephron of the kidney. The nephron is the functional unit of the kidney responsible for filtering blood to form urine. The process in the nephron that is most likely to be affected, leading to proteinuria, is the glomerular filtration process.
The glomerular filtration process occurs in the glomerulus, a network of tiny blood vessels (capillaries) in the renal corpuscle of the nephron. Here's a brief overview of how this process works:
1. Blood enters the glomerulus through the afferent arteriole, and within the glomerulus, the blood pressure is high due to the unique structure of the capillaries.
2. As blood flows through the glomerular capillaries, small molecules like water, electrolytes, and waste products are forced out of the blood and into the renal tubule by a process called filtration. This includes waste products like urea and creatinine, but normally, larger molecules like proteins are not filtered out because the glomerular filtration barrier acts as a selective barrier.
3. The glomerular filtration barrier consists of three layers: the endothelium of the capillaries, the basement membrane, and the podocytes (specialized cells that wrap around the capillaries). These layers prevent larger molecules like proteins from passing into the tubule while allowing smaller molecules to pass through.
4. The filtered fluid, called filtrate, then continues through the nephron, where essential substances are reabsorbed, and excess waste products are secreted into the tubule.