Presentation of the Forum is made possible by grants from Smith Kline & French Laboratories, CIBA Pharmaceutical Company, GEIGY Pharmaceuticals, and Hoechst-Roussel Pharmaceuticals, Inc. Nephrology Forum Mechanisms of urine concentration Principal discussant: Robert W. Berliner, 1 * 1 Yale University School of Medicine, New Haven, Connecticut Yale University School of Mechanism of Urine Concentration Three Essential Steps A major function of the kidney is conservation of water by increasing the solute concentration in the urine. The commonly cited mechanism for urine concentration in the IM is the passive mechanism proposed by Kokko and Rector (1972) and Stephenson (1972). Regulation of Urine Concentration. The process is called as counter current mechanism. Anita T. Layton, William H. Dantzler, Thomas L. Pannabecker. A hyperosmotic medullary interstitium is required for maximal urine concentrating ability. Impairment of the countercurrent mechanism. It has two parts; counter Because basic scientific principles form the backbone of all pathophysiologic reasoning, we present here a strictly physiologic discussion of the development of the countercurrent hypothesis of urine concentration and dilution. Concentrated Urine When there is a water deficit in the body, the kidney forms a concentrated urine by continuing to excrete solutes while increasing water reabsorption and decreasing the volume of urine formed. Too little ADH secretion Central Diabetes Insipidus. The mechanism generating the osmotic gradient in the inner medulla remains an unsolved mystery, although it is generally considered to involve countercurrent flows in the tubules and vessels. With dDAVP and 5 mmol/l urea in the perfusate, kidneys were unable to produce hyperosmotic urine and exhibited necrosis of the thick ascending limbs when perfused with erythrocyte-free medium. RU JUL10, DU Depends on ADH which controls water permeability in the last portion of DCT and collecting duct. The renal medulla produces concentrated urine through the generation of an osmotic gradient extending from the cortico-medullary boundary to the inner medullary tip. Reptiles and amphibians are able to excrete nitrogen-based waste products via their kidneys, but are unable to concentrate urine. the current model still fails to predict urine osmolalities of maximally concentrating rats. 3. Excess water is excreted. Thus, a concentration gradient of 300 mm in the cortex to 1200 mm in the medulla is created (milliosmoles or mOsm is a unit of osmolarity i.e. per minute during maximal water diuresis. ADVERTISEMENTS: Decreased ADH = dilute urine. LAMDIN E. Mechanisms of Urinary Concentration and Dilution. Figure 1 shows that the 4-day chloroquine treatment significantly reduced NKCC2 protein abundance by 39% compared with the untreated animals. Kidneys not only excrete harmful substances out from the body but also maintain the amount of water and salt in the body. The counter-current multiplier or the countercurrent mechanism is used to concentrate urine in the kidneys by the nephrons of the human excretory system. Start studying Urine concentrating mechanisms. Most water This is accomplished by the action of about a million nephrons working together with their attached collecting ducts. ADH ADH will alter the permeability of the membrane in the distal tubule and collecting duct by inserting aquaporin-2 channels. mechanisms which determine the ultimate concentration or dilution of the urine. In this chapter we consider the principle of countercurrent multiplication and the evidence for its application to the kidney. What is the Mechanism for the Formation of Concentrated Urine? Mechanisms to concentrate the urine: an opinion Lack of water permeability in the descending thin limbs of the loop of Henle offers several advantages. In an adult human, glomerular filtrate is about 180 L per day, most of which is reabsorbed by the high water permeable proximal tubule and descending limb of the Henle loop. Fig: Urine Formation. Mechanism of Concentration of Filtrate. In the presence of ADH, the medullary collecting ducts become freely permeable to solute and water. Physiology; NaCl is secreted via the cotransporter against its concentration gradient. This gradient is generated in the outer medulla by the countercurrent multiplication of a comparatively small transepithelial difference in osmotic pressure. per minute under conditions of dehydration to over 20 ml. It has been proposed, but not demonstrated experimentally, that urine concentration would be improved by the presence of a urea-Na + or urea-Cl cotransporter in the AQP1-null portion of the thin descending limb. 1959;103(4):644671. from the urine and transported against what appeared to be a large activity gradientin other words, by a process of active transport. Start studying urine concentration mechanism. Its mechanism is counterintuitive and complex. URINE CONCENTRATION MECHANISMS. A normal 70 kg human must excrete about 600 mOsm of solute each day. This urine-concentrating process involves generation of a gradient of increasing osmolality along the renal medulla from the corticomedullary junction to the tip of the papilla (as illustrated for the rat kidney in Figure 1) ( 1 3 ).
The countercurrent multiplier, also known as the countercurrent mechanism, is used by the nephrons of the human excretory system to concentrate urine in the kidneys. As a consequence, the fluid entering the ducts (en route to the renal pelvis and subsequent elimination) acquires the concentration of the interstitial fluid of the medulla; i.e., the urine becomes concentrated. AMA Arch Intern Med. osmolarity (urine osmolarity) between 50-1200 mOsm/L. obligatory urine volume it is the minimal volume of urine that must be excreted each day to get rid the body of the products of metabolism & ingested ions. However, regulation of water excretion mainly occurs after the luminal fluid reaches the distal tubule. 34. Physiology lecture on renal system physiology details countercurrent mechanism for the concentration and dilution of urine. Effects of reduced glomerular filtration on urine concentration in the presence of antidiuretic hormone. A significant role for RBCs in the urine concentrating mechanism is supported by experiments that have been carried in isolated, perfused rat kidneys . The nephrons that are the kidney's functional unit are involved in concentrated urine formation. The countercurrent * concentrating mechanism. Protein expression of some components of the urine concentration mechanism is altered by chronic chloroquine treatment. total solutes to be excreted each day in 70 kg man = 600 mosmol maximum conc. One of the most efficient water conservation mechanisms in mammals is the ability of the kidneys to produce concentrated urine for the elimination of waste products while losing a minimum of water. Urine-concentrating mechanism in the inner medulla: function of the thin limbs of the loops of Henle Abstract The ability of mammals to produce urine hyperosmotic to plasma requires the generation of a gradient of increasing osmolality along the medulla from the corticomedullary junction to Solute concentration is low. Concentrating mechanism of the kidney In order to excrete the excess of ingested electrolytes, or in case of inadequate water supply, the kidney excretes concentrated urine, so that excess solutes are eliminated with a little loss of water from the body, The basic requirements for forming concentrated urine are: The nephron loop of juxtamedullary nephrons is the apparatus that allows the nephron to concentrate urine. Concentration is the unique property of mammals and some birds by virtue of an extraordinary concentrating system. General Features of Urine Concentration. The loop is a countercurrent multiplier system in which fluids move in opposite directions through sidebyside, semipermeable tubes. No matter how much ADH is present, maximal urine concentration is limited by the degree of hyperosmolarity of the medullary interstitium. The human kidney can produce a maximal urine concentration of 1200 to 1400 mOsm/L, four to five times the osmolarity of plasma. Learn vocabulary, terms, and more with flashcards, games, and other study tools. [PMC free article] [Google Scholar] BERLINER RW, LEVINSKY NG, DAVIDSON DG, EDEN M. Dilution and concentration of the urine and the action of antidiuretic hormone. Urine concentrating mechanism: Impact of vascular and tubular architecture and a proposed descending limb urea-Na + cotransporter. The body utilizes two different mechanisms to maintain an optimal osmolarity in the blood: ADH (anti-diuretic-hormone) and countercurrent multiplier mechanism. The filtrate from the Bowmans capsule enters the PCT, which is almost isotonic to the blood plasma. The U/P ratio expresses the relationship between the concentration of a substance in the urine and its concentration in plasma, affording an index of the extent to which a substance is diluted (U/P<1) or concentrated (U/P>1). ability of human kidney = 1200 mosmol/l ouv = In this issue of The Forum we make a modest departure from our usual, case-oriented discussion. 2. The urine concentrating mechanism of the mammalian kidney, which can produce a urine that is substantially more concentrated than blood plasma during periods of water deprivation, is one of the enduring mysteries in traditional physiology. it depends upon the maximal concentrating ability of the kidney. We first examined if NKCC2 protein abundance was affected by chloroquine treatment. LEVINSKY NG, DAVIDSON DG, BERLINER RW.
1959 May; 38 (5):730740. The urine concentrating mechanism is believed to operate as follows in the outer medulla. These deep AQP1-null segments, prebend segments, and thin ascending limbs lie equally near the collecting ducts. In man, the urine flow may range from less than 0.5 ml. Increased ADH = concentrated urine. Depending on the food supply of differing animals, components of the glomerular ultrafiltrate are concentrated in the final urine to different extents. J Clin Invest. Learn vocabulary, terms, and more with flashcards, games, and other study tools. In the inner medulla, the source of the osmotic gradient has not been identified. The diagnosis of dRTA was based upon a urine pH of 6.9 for each case during an acute metabolic acidosis (blood pH 7.01 and 7.14), a normal HCO3 threshold First, since much less water is added to the outer medullary interstitial compartment, inhibitory control mechanisms on sodium and chloride reabsorption from the medullary thick ascending of loop Whenever body needs to conserve water, concentrated urine is formed. The maximal concentrating ability of the kidney depends on how much urine volume must be excreted each day, to void the body of waste products of metabolism and ions that are ingested. Urine is concentrated in the final stages of its production: water is absorbed, in excess of solute, from the collecting ducts and into the vasculature of the medulla, thus increasing the osmolality of the collecting duct fluid and thus the osmolality of the urine that emerges from the collecting ducts.