Abstract:The mammalian kidney is responsible for a multitude of homeostatic functions, which are mediated by both structural and functional diversity along the renal tubule. In this article, we focus on the major functions of the terminal portion of the renal tubule, the medullary collecting duct system. The role of the medullary collecting ducts in determining the composition of the final urine through controlled water, sodium, chloride, potassium and urea reabsorption, ammonia transport, and acid-base homeostasis is … Show more
“…Urea and water permeabilities, and their regulation by vasopressin vary among IMCD1, -2, and -3. A number of reviews focus on the intricacies of rat and mouse CD tubular and cellular functionality (11,27).…”
Section: Segmentation Of Medullary Nephrons and Blood Vesselsmentioning
Comparative studies of renal structure and function have potential to provide insights into the urine-concentrating mechanism of the mammalian kidney. This review focuses on the tubular transport pathways for water and urea that play key roles in fluid and solute movements between various compartments of the rodent renal inner medulla. Information on aquaporin water channel and urea transporter expression has increased our understanding of functional segmentation of medullary thin limbs of Henle's loops, collecting ducts, and vasa recta. A more complete understanding of membrane transporters and medullary architecture has identified new and potentially significant interactions between these structures and the interstitium. These interactions are now being introduced into our concept of how the inner medullary urine-concentrating mechanism works. A variety of regulatory pathways lead directly or indirectly to variable patterns of fluid and solute movements among the interstitial and tissue compartments. Animals with the ability to produce highly concentrated urine, such as desert species, are considered to exemplify tubular structure and function that optimize urine concentration. These species may provide unique insights into the urine-concentrating process.(1)
“…Urea and water permeabilities, and their regulation by vasopressin vary among IMCD1, -2, and -3. A number of reviews focus on the intricacies of rat and mouse CD tubular and cellular functionality (11,27).…”
Section: Segmentation Of Medullary Nephrons and Blood Vesselsmentioning
Comparative studies of renal structure and function have potential to provide insights into the urine-concentrating mechanism of the mammalian kidney. This review focuses on the tubular transport pathways for water and urea that play key roles in fluid and solute movements between various compartments of the rodent renal inner medulla. Information on aquaporin water channel and urea transporter expression has increased our understanding of functional segmentation of medullary thin limbs of Henle's loops, collecting ducts, and vasa recta. A more complete understanding of membrane transporters and medullary architecture has identified new and potentially significant interactions between these structures and the interstitium. These interactions are now being introduced into our concept of how the inner medullary urine-concentrating mechanism works. A variety of regulatory pathways lead directly or indirectly to variable patterns of fluid and solute movements among the interstitial and tissue compartments. Animals with the ability to produce highly concentrated urine, such as desert species, are considered to exemplify tubular structure and function that optimize urine concentration. These species may provide unique insights into the urine-concentrating process.(1)
“…The final adjustment of urine pH is a main task of renal intercalated cells (13). In type A cells, the vacuolar H ϩ -ATPase is actively pumping protons into the tubular lumen, while in type B cells it pumps protons to the blood side.…”
“…The collecting duct participates in the final step of ammonia/ammonium excretion. In the collecting duct, the major site of this excretion is the OMCD (151, 285, 603). However, during metabolic acidosis, a strong increase in ammonia and ammonium transport is also found in the CNT, CCD and IMCD (285, 603).…”
Section: Introductionmentioning
confidence: 99%
“…The process of urea accumulation is mostly dependent on facilitated urea transport across the epithelium of the IMCD (149, 286). This urea transport process and its regulation have been reviewed extensively (149, 150, 286, 470, 472) and recent updates are discussed in the corresponding overview article (151). …”
The central goal of this overview article is to summarize recent findings in renal epithelial transport, focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD). Mammalian CCD and CNT are involved in fine tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, e.g. aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades. Recent studies shed new light on several key questions concerning the regulation of renal transport. Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will be also covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD.
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