Ultrafiltration is filtration at the molecular level- holding back plasma proteins. This is performed using a network of filtration slits in the capsule epithelial cells, which only hold back blood cells. The blood capillary walls are fenestrated or perforated and allow the plasma of blood through. The basement membrane acts as the dialysis membrane where ultrafiltration occurs. Explain the process of selective reabsorption in the proximal convoluted tubule including the roles of microvilli, pinocytosis and active transport.
Selective reabsorption modifies the concentration of the filtrate.
The microvilli or brush border helps reabsorption in that it provides extensive surface area. Finally, active transport is used to transport nutrients not suited for diffusion or pinocytosis, such as glucose and amino acids. Explain the production of hypertonic urine including the roles of the loop of Henle, medulla, collecting duct, ADH, and water potential gradients. The loop of Henle serves to concentrate the urine with waste, therefore animals which need to conserve water, such as those in the desert, have a longer loop of Henle and more concentrated urine. The medulla is the inner zone of the kidney and helps to form urine which then drains into the renal pelvis which leads to the ureter.