In clinical practice, we use more complex calculations, corrected for body surface area and other physical parameters — e. The majority of the descending loop is comprised of simple squamous epithelial cells; to simplify the function of the loop, this discussion focuses on these cells. The transport of glucose from the lumen of the PCT to the interstitial space is similar to the way it is absorbed by the small intestine.
Urea, NH 3 , creatinine, and some drugs are filtered or secreted as wastes.
Figure 3. If aquaporin water channels are present, water will be osmotically pulled from the collecting duct into the surrounding interstitial space and into the peritubular capillaries. This control is exerted directly by ADH and aldosterone, and indirectly by renin. The movement of many positively charged ions also creates an electrochemical gradient. Most of the resulting ammonia is converted into urea by liver hepatocytes.
Its effect increases the number of aquaporins in cell membranes and water molecules can pass along the osmotic gradient into peritubular fluid ECF. The Cellular Level of Organization 3.
Medullary Concentration Gradient 25. The Nervous System and Nervous Tissue 12.
If we want to determine GFR, which is one of the basic function of our kidneys , we have to use a substance that is excreted from the body only by glomerular filtration inulin, creatinine and is not affected by tubular processes. Control of urine osmolarity There are several processes controlling the urine osmolarity.
Sodium moves down its electrochemical and concentration gradient into the cell and takes glucose with it. In the vasa recta particularly, this rate of flow is important for two additional reasons. The loops of cortical nephrons do not extend into the renal medulla very far, if at all. Blood Vessels and Circulation 20. Both mechanisms may utilize concentration gradients maintained by ATP pumps.
The distal part of the distal convoluted tubule and the collecting duct consist of two cell types: Collecting ducts consist of principal intercalated cells.
The Appendicular Skeleton 8.
The countercurrent term comes from the fact that the descending and ascending loops are next to each other and their fluid flows in opposite directions countercurrent. We can distinguish local and central regulatory mechanisms.
Sodium is actively pumped out of the PCT into the interstitial spaces between cells and diffuses down its concentration gradient into the peritubular capillary. This is because some nephrons have longer proximal tubules than others so although some may be overcome and therefore allowing glucose to be excreted others are managing to fully reabsorb the glucose along their length.
Most absorption and secretion occurs in this part of the nephron. As the ducts descend through the medulla, the osmolarity surrounding them increases due to the countercurrent mechanisms described above.
Angiotensin II stimulates aldosterone secretion and resorption of sodium ions and consequently resorption of water molecules in the proximal tubule.