Countercurrent exchange in the renal medulla

Pallone, Thomas L.; Turner, M. R.; Edwards, Aurélie; Jamison, Rex L.

doi:10.1152/ajpregu.00657.2002

Cited by 139 publications

(107 citation statements)

References 139 publications

(257 reference statements)

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“…The DVR in the innermost 50% of the rat and kangaroo rat inner medulla also express little or no UT-B (15,49). However, functional studies in rats have shown that vasa recta from the deep papilla exhibit substantial urea Smooth muscle myosin heavy chain protein is expressed in renal arterioles (26,44), and its expression along the upper inner medullary DVR in the human kidney suggests that segments in the upper zone of the inner medulla have contraction and relaxation properties, as has been shown for DVR of the inner stripe of the outer medulla (32). The contractile properties of segments at deeper levels of the inner medulla, where smooth muscle myosin heavy chain protein expression is distributed more sparsely or is absent altogether, likely are different.…”

Section: Discussionmentioning

confidence: 90%

“…The inner stripe therefore consists of many vascular bundles running parallel to the corticomedullary axis, with each bundle carrying countercurrent flows. In both human and rat, the DVR feed into complex capillary networks that perfuse the interbundle region, with many capillaries feeding, in turn, to AVR (32). These DVR are lined by pericytes, which have a smooth muscle component whose contractile properties have the potential for regulating blood flow in both the inner stripe and the inner medulla (32).…”

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confidence: 99%

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Architecture of the human renal inner medulla and functional implications

Wei

Rosen

Dantzler

et al. 2015

American Journal of Physiology-Renal Physiology

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The architecture of the inner stripe of the outer medulla of the human kidney has long been known to exhibit distinctive configurations; however, inner medullary architecture remains poorly defined. Using immunohistochemistry with segment-specific antibodies for membrane fluid and solute transporters and other proteins, we identified a number of distinctive functional features of human inner medulla. In the outer inner medulla, aquaporin-1 (AQP1)-positive long-loop descending thin limbs (DTLs) lie alongside descending and ascending vasa recta (DVR, AVR) within vascular bundles. These vascular bundles are continuations of outer medullary vascular bundles. Bundles containing DTLs and vasa recta lie at the margins of coalescing collecting duct (CD) clusters, thereby forming two regions, the vascular bundle region and the CD cluster region. Although AQP1 and urea transporter UT-B are abundantly expressed in long-loop DTLs and DVR, respectively, their expression declines with depth below the outer medulla. Transcellular water and urea fluxes likely decline in these segments at progressively deeper levels. Smooth muscle myosin heavy chain protein is also expressed in DVR of the inner stripe and the upper inner medulla, but is sparsely expressed at deeper inner medullary levels. In rodent inner medulla, fenestrated capillaries abut CDs along their entire length, paralleling ascending thin limbs (ATLs), forming distinct compartments (interstitial nodal spaces; INSs); however, in humans this architecture rarely occurs. Thus INSs are relatively infrequent in the human inner medulla, unlike in the rodent where they are abundant. UT-B is expressed within the papillary epithelium of the lower inner medulla, indicating a transcellular pathway for urea across this epithelium.

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Section: Discussionmentioning

confidence: 90%

mentioning

confidence: 99%

Architecture of the human renal inner medulla and functional implications

Wei

Rosen

Dantzler

et al. 2015

American Journal of Physiology-Renal Physiology

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“…Thus, the medulla is in a hypoxic environment under a physiological state [1] . Such an arrangement is strategically necessary to maintain the corticomedullary osmotic gradient for fluid absorption and urine concentration [2] . To avoid energy deprivation in the low pO 2 regions, an array of hormones, autocoids, and vasoactive substances, mostly synthesized in the medulla, including medullipin, prostaglandins, endothelins, nitric oxide, angiotensin II, kinins, and adenosine are required [1,3] .…”

Section: Kidneys Are Vulnerable To Inflammatory Insultsmentioning

confidence: 99%

Inflammation: A Key Contributor to the Genesis and Progression of Chronic Kidney Disease

Qian

2017

Expanded Hemodialysis: Innovative Clinical Approach in Dialysis

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It has become apparent that inflammation and inflammatory reactions can evoke renal injury and promote chronic kidney disease (CKD) progression. Under physiological condition, intrarenal vascular distribution is heterogeneous, and medulla is hypoxic. To avoid energy deprivation in the low pO 2 regions of the kidney, an array of hormones, autocoids, and vasoactive substances, including medullipin, prostaglandins, endothelins, nitric oxide, angiotensin II, kinins, and adenosine, tonically regulates the microvasculature to ensure a perfect match of the microcirculation (O 2 supply) and renal tubules (O 2 demand). Inflammation, systemic or intrarenal, not only can abolish the microvascular response to its regulators, but also induces an array of tubular toxins, including reactive oxygen species, leading to tubular injury, nephron dropout, and onset of CKD. Positive acid balance, electrolyte alterations, and intestinal dysbiosis can perpetuate CKD progression. Understanding the role of inflammation in the genesis and progression of CKD will foster the development of strategies to prevent and treat the underlying inflammation and improve CKD outcomes.

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“…In mice, descending limbs of short loops migrate within vascular bundles and lie adjacent to peripheral vasa recta. DVR endothelia and red blood cells (RBCs) express aquaporin (AQP)-1 water channels and urea transporter (UT)-B so that their equilibration occurs by a combination of solute influx and solute-free water removal (6,7). DVR and AVR are not simply diffusive countercurrent exchangers.…”

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confidence: 99%

Complex vascular bundles, thick ascending limbs, and aquaporins: wringing out the outer medulla

Pallone

2014

American Journal of Physiology-Renal Physiology

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DESPITE ITS SMALL MASS, the renal inner medulla plays a pivotal role in homeostasis. It adjusts the solute, water, and proton content of the final urine to match the excretory needs of the organism. The large glomerular filtrate is reabsorbed by highflow, low-gradient processing in the proximal nephron along with key transport steps that occur within the outer medulla. In combination, they protect the inner medulla from the need to process large tubular and vascular volume flows. In a recent issue of the American Journal of Physiology-Renal Physiology, Ren and colleagues (9) provide important insights into the anatomic relationships that underlie the ability of the outer medulla to participate in that scheme.Hemisection of the kidney reveals cortical, outer medullary, and inner medullary zonation. The outer medulla is subdivided into the outer stripe and inner stripe. The inner stripe is further divided into vascular bundles and the interbundle region (1,3,8). Counterflow of blood epitomizes vascular bundle function; ascending vasa recta (AVR) lie adjacent to descending vasa recta (DVR) to accommodate efficient exchange of solutes and water between them. The "simple" vascular bundle exemplified by rabbit and humans contains only DVR and AVR. The "complex" vascular bundle of highly concentrating rodents incorporates descending thin limbs of short-looped nephrons to a degree that varies with individual species. In mice, descending limbs of short loops migrate within vascular bundles and lie adjacent to peripheral vasa recta. DVR endothelia and red blood cells (RBCs) express aquaporin (AQP)-1 water channels and urea transporter (UT)-B so that their equilibration occurs by a combination of solute influx and solute-free water removal (6, 7). DVR and AVR are not simply diffusive countercurrent exchangers. AVR shunt any water osmotically withdrawn across DVR endothelia back to the cortex. In all species, AQP-1-expressing descending thin limbs of long-looped nephrons and AQP-2-expressing collecting ducts are excluded to the interbundle region.Ren and colleagues (9) generated three-dimensional reconstructions of tubules and vessels of the murine outer medulla by digitizing serial sections and tracing the structures from the midlevel of the inner stripe toward the cortex and inner medulla. Proper identification was assured by noting the origins and terminations of thin-walled tubules and vessels. In addition, immunostaining for AQP-1 was performed to localize its expression by DVR endothelia and descending limbs of long-looped nephrons. It is noteworthy that AQP-1-expressing structures in vascular bundles (DVR and RBCs) and the interbundle region (i.e., thin descending limbs of long loops) lie near thick ascending limbs. They found that thick ascending limbs of long-looped nephrons surround the vascular bundle at its border and sometimes migrate into the vascular bundle periphery. Other features were also confirmed by the investigators. DVR arise soley from juxtamedullary efferent arterioles. Periglomerular origins of DVR...

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Countercurrent exchange in the renal medulla

Cited by 139 publications

References 139 publications

Architecture of the human renal inner medulla and functional implications

Architecture of the human renal inner medulla and functional implications

Inflammation: A Key Contributor to the Genesis and Progression of Chronic Kidney Disease

Complex vascular bundles, thick ascending limbs, and aquaporins: wringing out the outer medulla

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