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The Loop of Henle and Production of Concentrated Urine
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The vasa recta supply blood to the medulla. They are capillary loops in parallel with and closely applied to the descending and ascending limbs of the loops of Henle. As they descend into the medulla, water is lost from, and solute (NaCl and urea) is absorbed into, the descending vessels, and at the tip of the hairpin, the fluid may have an osmolality of 1200 mOsm/kg H2O. However, the process is reversed (i.e. water enters and solute leaves) in the ascending vasa recta, so that fluid leaving the vessels has an osmolality of only 320 mOsm/kg H2O. This counter-current exchange between the descending and ascending vessels ensures that the blood flow to the medulla does not wash away the interstitial medullary gradient created by the loop of Henle and traps solute in the medulla. This is a passive process facilitated by the slow flow of blood in the vasa recta (Figure 44.2). Changes in blood flow can affect the gradient. When the blood flow is increased, the solutes are washed out of the medulla and its interstitial osmolality is decreased. The reverse occurs when blood flow is decreased.
Kidney Microcirculation
Published in John H. Barker, Gary L. Anderson, Michael D. Menger, Clinically Applied Microcirculation Research, 2019
In the human, glomerular filtration rate is approximately 1501/day. Obviously, if there were no tubular reabsorption, profound volume depletion would occur. Tubular reabsorptive processes reclaim about 99% of the filtered salt and water. Tubular reabsorption involves both active and passive transport mechanisms. While volume reclamation from proximal tubular lumens is largely the consequence of active ion transport, vascular uptake of fluid from the interstitium is dependent on the high colloid osmotic pressure in the peritubular capillaries resulting from glomerular filtration, and this imparts a strong net driving force for volume reabsorption. The vasa rectae have a special exchange function. The high osmolar tonicity of the medullary interstitium is maintained by a combination of the countercurrent multiplication of sodium and urea by cycling from the ascending to the descending loops of Henle and countercurrent exchange of ions and urea from ascending to descending vasa rectae vessels. Changes in flow rates through the vasa rectae can alter the interstitial osmolality and, thereby, the maximal concentrating capacity of the kidney.
SBA Answers and Explanations
Published in Vivian A. Elwell, Jonathan M. Fishman, Rajat Chowdhury, SBAs for the MRCS Part A, 2018
Vivian A. Elwell, Jonathan M. Fishman, Rajat Chowdhury
Flow to the renal medulla is supplied by long capillary loops called the vasa recta. These descend into the medulla in parallel with the loops of Henle. The blood flow in them is very low compared with flow in the renal cortex. This helps to maintain the hyperosmotic medullary interstitial gradient, thereby assisting in the formation of a concentrated urine.
Preventing acute kidney injury during transplantation: the application of novel oxygen carriers
Published in Expert Opinion on Investigational Drugs, 2019
Raphael Thuillier, Eric Delpy, Xavier Matillon, Jacques Kaminski, Abdelsalam Kasil, David Soussi, Jerome Danion, Yse Sauvageon, Xavier Rod, Gianluca Donatini, Benoit Barrou, Lionel Badet, Franck Zal, Thierry Hauet
The major function of kidney is to remove waste products and excess fluid from the body to maintain homeostasis. Kidney tissue oxygenation is determined by the presence of oxygen in arterial blood, oxygen consumed by the cells, and arterial-to-venous oxygen shunting [9]. Renal oxygenation is defined as the relationship between renal oxygen delivery (DO2) and renal oxygen consumption (VO2). The anatomy of the nephron and renal microcirculation plays a crucial role in understanding the effect of ischemia on the kidney. In physiological conditions, kidneys receive approximately 20% of cardiac output and this blood flow is channeled to the cortex with blood flow to the medulla predominantly from the vasa recta, a continuation of efferent arterioles of the juxtamedullary glomeruli. In hospital settings, AKI commonly occurs in sepsis, and after procedures associated with temporary cessation of renal perfusion or reduced renal blood flow or oxygen delivery. Such procedures include renal transplantation, cardiac, and other major surgery, resection of renal mass, and reparation of an aneurysm [10]. Blood flow to the kidney is temporarily occluded during surgical procedures such as renal transplantation (cold ischemia), and consequentially, oxygen delivery to the kidney ceases, the kidney becoming hypoxic and anoxic. Hypothermia remains the cornerstone of the methodological approach for organs preservation.
Cholangitis Lenta Causing Bile Cast Nephropathy: A Unique Model of Hepatorenal Failure in Sepsis
Published in Fetal and Pediatric Pathology, 2018
Christopher Antonio Febres Febres Aldana, Robert J Poppiti
As seen as in the liver, the kidneys showed the histopathology of “shock” and BCN. Vasoconstriction of the descending vasa recta results in redirection of blood into inter-bundle plexuses, creating a shunt of the renal microvasculature (Trueta shunt), seen as severe vascular congestion in the outer medulla (Figure 3C). A pale cortex and hyperemic medulla have been historically considered gross features of acute ischemic renal failure [14]. Ischemic ATN after pronounced vasoconstriction is amongst the consequences of blood flow redistribution. In a postmortem study of children with sepsis-induced kidney injury, defined as acute alterations in serum creatinine levels or urine output according to the Acute Kidney Injury Network (AKIN) classification system, normal histology was the most common finding involving 41% of the cases followed by ATN in 30% and thrombotic microangiopathy in 8% [3]. Complex combinations of changes in tubules, interstitium, glomeruli and blood vessels were identified in 21% of the cases supporting that tubular damage in sepsis is essentially multifactorial. Ischemic damage by itself does not fully explain the hepatorenal failure seen in this case because the hepatic centrilobular necrosis was in an early stage and there was no evidence of ischemic ATN. Despite the presence of tubular injury, ischemic ATN was excluded based on the absence of necrosis or regenerative changes in the proximal tubular epithelia and cellular casts in distal tubules.
Role of chymase in blood pressure control, plasma and tissue angiotensin II, renal Haemodynamics, and excretion in spontaneously hypertensive rats
Published in Clinical and Experimental Hypertension, 2021
Malwina M. Roszkowska-Chojecka, Iwona Baranowska, Olga Gawrys, Janusz Sadowski, Agnieszka Walkowska, Malgorzata Kalisz, Anna Litwiniuk, Elzbieta Kompanowska-Jezierska
Surprisingly, we observed a differential response to chymostatin in OMBF (increase in young and adult rats) compared to the changes observed in cortical and innermedullary blood flow. It is important to underline that structural (eg. proximity of sympathetic nerve varicosities and/or density of pericytes localized around vasa recta) and functional characteristics of outer and inner medullary vasa recta are significantly different from each other (23–25) and therefore these perfusion zones may react differently to similar stimuli. Since there is still limited knowledge about stimuli specific only to OMBF it is difficult to define definitively what was responsible for the different OMBF response to chymostatin administration vs CBF and IMBF.