The Loop of Henle and Production of Concentrated Urine
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
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.
Renal physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
The vasa recta consists of the descending vasa recta, which follows the long loops of Henle into the inner medulla and is then drained by the venous ascending vasa recta. Blood flow is in the opposite direction to that of the tubular fluid (filtrate). The vasa recta is freely permeable to salt and water and its blood flow is extremely slow, allowing time for passive equilibration between the capillaries and the tubules. The vessel loop formed by the descending vasa recta and the ascending vasa recta forms the counter-current exchange mechanism. In summary, the vasa recta traps solutes in the medulla so that the high solute concentration of medullary interstitial fluid is maintained.
SBA Answers and Explanations
Vivian A. Elwell, Jonathan M. Fishman, Rajat Chowdhury in SBAs for the MRCS Part A, 2018
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.
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.
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.
Related Knowledge Centers
- Efferent Arteriole
- Loop of Henle
- Nephron
- Peritubular Capillaries
- Renal Circulation
- Renal Medulla
- Blood Vessel
- Kidney
- Loop of Henle
- Interlobular Veins
- Countercurrent Exchange