G29 Urine Concentration and Dilution PDF

12/20/24 Urine concentration and Dilution 1 Derek Owens DrAP, CRNA 1 2 Module 3 ´ Guyton 26, 27, 28, 29, 30 ´ Learning Objectives 1. Describe the structure and function of the renal and urologic systems. 2. Differentiate...

12/20/24 Urine concentration and Dilution 1 Derek Owens DrAP, CRNA 1 2 Module 3 ´ Guyton 26, 27, 28, 29, 30 ´ Learning Objectives 1. Describe the structure and function of the renal and urologic systems. 2. Differentiate the various functions of the kidney and how it maintains optimal cell and tissue metabolism. ´ Guyton chapter 29 2 3 Total body water ´ Fluid intake ´ Thirst !"#$%&' () ´ Renal water excretion Osmolarity = +#$,-."#$/& ´ Dilute Urine ´ Concentrated Urine ´ Feedback mechanisms ´ Salt and water intake 3 1  12/20/24 4 Urine osmolarity control ´ 50 mOsm/L -1400 mOsm/L Normal = 280-300 mOsm/L 4 5 ADH controls urine concentration ´ Posterior pituitary ↓ ADH = ↑ Urine ↑ ADH = ↓ Urine 5 6 Renal mechanism for excreting dilute urine 6 2  12/20/24 7 Proximal tubules and descending loop of Henley ´ Isosmotic 7 8 Ascending loop of Henley ´ Solute reabsorption 8 9 Distal and collecting tubules ´ Reabsorb sodium chloride ´ Possibly reabsorbs water 9 3  12/20/24 10 Conservation of water ´ Lungs 011 /2'//-)4 = 0.5L/day 5611 /2'//7 ´ G.I. tract ´ Skin ´ Kidneys 10 11 Excreting concentrated urine ´ ADH ´ High osmolarity of the renal Medulary interstitial fluid 11 Countercurrent 12 multiplier mechanism 1. Active transport in the ascending limb 2. Active transport in the collecting ducts 3. Facilitated diffusion of urea in the collecting ducts 4. Diffusion of only small amounts of water 12 4  12/20/24 Loop of Henley solute trapping 1. Thick ascending active pump 2. 200 mOsm/L concentration gradient limit 3. Descending limb fluid diffusion 13 13 14 Distal tubule and collecting ducts excreting concentrated urine 14 Urea reabsorption contributes to 15 the osmolarity of the renal medullary interstitium ´ Little urea is reabsorbed until the collecting ducts. ´ Reabsorption facilitated by UT-A1 and UT-A3 transporters 15 5  12/20/24 16 Urea excretion 1. Concentration in plasma 2. Glomerular filtration rate 3. Renal tubular urea reabsorption 16 Blood supply to the renal medulla and the Vasa Recta countercurrent exchange ´ Medullary blood flow is low ´ Less than 5% of total renal blood flow ´ Countercurrent exchange of the Vasa Recta ´ Minimized washout of solutes 17 17 18 Summary of urine concentrating mechanism and osmolarity changes 18 6  12/20/24 19 Proximal tubule ´ 300 mOsm/L 19 20 Descending loop of Henley ´ High permeability to water ´ AQP-1 20 21 Thin Ascending loop of Henley ´ Impermeable to water ´ Reabsorbs sodium 21 7  12/20/24 22 Thick Ascending loop ´ 100 mOsm/L 22 Early distal tubule ´ 300 mOsm/L 23 23 24 Late distal tubular and cortical collecting tubules ´ ADH sensitive 24 8  12/20/24 Inner Medullary collecting ducts ´ Fluid reabsorption ´ ADH sensitive ´ Medullary interstitium osmolarity ´ Sodium excretion is highly regulated ´ Minimal obligatory urine volume 25 25 26 Control of exercising fluid osmolarity and sodium concentration 1. Osmoreceptor-ADH system 2. Thirst mechanism ´ Na 140-145 ´ 94% osmoles 26 27 Osmoreceptor ADH feedback system 1. Increased osmolarity = osmoreceptor cells shrink 2. Signal set to the posterior pituitary 3. ADH is released into the bloodstream 4. ADH stimulates the late distal tubules, cortical collecting ducts, and medullary collecting ducts 5. Small amounts of concentrated urine 27 9  12/20/24 ADH synthesis ´ Supraoptic ´ Paraventricular nuclei ´ Anteroventral region of the third ventricle 28 28 29 Stimulation of ADH release ´ Arterial baroreceptor reflexes ´ Cardiopulmonary reflexes ´ Osmoreceptors 29 Thirst ´ Anteroventral region of the third ventricle 30 30 10  12/20/24 31 Stimuli for thirst ´ Extracellular fluid osmolarity ´ Extracellular fluid volume ´ Arterial pressure ´ Angiotensin II ´ Mouth and esophageal mucus membrane dryness ´ Gastrointestinal and pharyngeal stimuli 31 Osmolar threshold for drink ´ Threshold for drinking ´ 2meq/L above normal 32 32 11