It is quite vulnerable in some ways even though it is a very resilient organ. Kidney function: nephron, glomerulus, proximal convoluted tubule, distal convoluted tubule, collecting duct, urine formation, glomerular filtration, blood flows through bowman"s capsule (first part of nephron). If the sodium content is too high or too low, it can alter the pressure of the blood flowing through the glomerulus to increase or decrease the filtration pressure. Here, you can directly make smooth muscle cells contract or relax to increase or decrease blood flow: external factors also alter the contraction or relaxation state. They also make a selection of molecules that coat the basement membrane. In fact, it is the most vulnerable area because it is absorbing all of these things back in again. It has active transport systems for reabsorption and water follows. It is actively transporting glucose, amino acids, sodium, chloride, vitamins and so on: active energy requiring transport is at the basolateral membrane.