9.1 A creatinine molecule would enter the glomerulus in the blood via an afferent arteriole, and be filtered into the glomerular capsule, which is continuous with the renal tubule (Applegate, 2000, 376). It would flow down in the filtrate through the proximal convoluted tubule, down the descending limb into the loop of Henle, up the ascending limb and into the distal convoluted tubule. From here, it would enter a collecting duct which extends from the base of the pyramids to the renal papillae and flow through the collecting tube into the one of the minor calyces that surround the papillae. The creatinine molecule would then flow through a minor calyx into a major calyx, which would direct its flow into the ureter.
9.2 Plasma is the liquid portion of blood which contains roughly 90 percent water, and the remaining 10 percent is made up of over 100 different organic and inorganic solutes (Applegate, 2000, 227). These include proteins, globulins, and fibrinogen, as well as ions and nutrients. As blood flows through the kidney, about 19 percent of the plasma enters the glomerulus as a renal filtrate of blood (381). Blood cells and protein molecules are absent from the renal filtrate, and this is the difference between plasma and the renal filtrate if the kidney is functioning normally. The filtration membrane in the renal corpuscle consists of the epithelium of the capillary of the glomerulus and the endothelium of the capsule. The podocytes of the visceral layer of Bowman's capsule extend processes around the glomerular capillaries, and each process has numerous pedicels or foot processes which interdigitate with those of their neighbors (Ross, Romrell and Kaye, 1995, 566). The elongated spaces between foot processes are the filtration slits, and are about 25 nm wide, and limit the size of molecules which can filter through them from the blood. Microfilaments also limit the size of the filtration slits.
The thick ba...