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Renal water handling in states of maximum antidiuresis and maximum diuresis. Numbers to the right indicate interstitial osmolality; numbers in the tubules
indicate luminal osmolality. The dashed line indicates the cortico-medullary border. Arrows indicate sites of water movement. In both antidiuresis and
diuresis, most (65%) of the filtered water is reabsorbed in the proximal tubule and another 10% in the descending loop of Henle. The greater relative
reabsorption of solute versus water by the loop as a whole and distal tubule results in luminal fluid that is quite dilute (110 mOsm) as it enters the collecting
ducts. During antidiuresis (A) the actions of antidiuretic hormone permit most remaining water to be reabsorbed in the cortical collecting duct. Additional
reabsorption in the medullary collecting ducts results in a final fluid that is very hyperosmotic (1200 mOsm). During diuresis (B) no water reabsorption
Source: Chapter 6. Basic Renal Processes for Sodium, Chloride, and Water, Vander’s Renal Physiology, 8e
occurs in the cortical collecting tubule, but some occurs in the inner medullary collecting tubule independent of ADH. Despite the medullary water
Eaton
DC, Pooler
JP.reabsorption
Vander’s Renal
Physiology,
2013relatively
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13, 2017
reabsorption,Citation:
continued
medullary
solute
reduces
solute 8e;
content
than water content and
the final
urine
is very dilute (70
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mOsm). In the parallel vasa recta, there is considerable exchange of both solute and water. The ascending vasa recta ultimately remove all the solute and
water reabsorbed in the medulla. Because there is always some net volume reabsorption in the medulla, the vasa recta plasma flow out of the medulla
always exceeds the plasma flow in.