Regulation of Water Balance
Lisa M. Harrison-Bernard, Ph.D.
Reading: Chapter 5 in Koeppen & Stanton Renal Physiology (Mosby Physiology Monograph Series)
LEARNING OBJECTIVES
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Explain how the transport and permeability characteristics of the descending and ascending segments of the loop of Henle enable the kidney to produce a concentrated urine.
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Describe how the renal tubular handling of urea contributes to the production of a concentrated urine. Know that urea is filtered, reabsorbed and secreted and that urea recycling is responsible for the buildup of high [urea] in the inner medulla.
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Describe the mechanism by which AVP alters the water permeability of the collecting duct.
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Explain the effect of changes in the water permeability of the collecting duct on the volume and composition of the final urine.
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Describe the site and mechanism of AVP secretion.
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Identify the two most powerful stimuli that cause ADH release, and describe the negative feedback control mechanisms for each.
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Identify the tubular section and cellular mechanism by which ADH increases permeability to water and urea. Describe the role of these changes on the ability of the kidney to produce either a dilute or a concentrated urine.
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Predict the changes in body fluid volume and osmolality caused by a net NaCl loss or gain in the body. Predict how each of these disturbances would alter the rate of urine production and the osmotic composition of the urine.
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Predict the consequence on urine concentrating ability if the medullary osmotic gradient is disrupted. Following disruption, describe how the osmotic gradient would be re-established.
Learning objectives have been adapted from the Renal Physiology Objectives (http://www.the-aps.org/education/MedPhysObj/medcor.htm) developed by the American Physiological Society (http:www.the-aps.org).