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Relationship between plasma antidiuretic hormone (ADH) concentration and urine osmolality and urine production rate.
Relationship between plasma antidiuretic hormone (ADH) concentration and urine osmolality and urine production rate. Click for higher resolution image.
Relationship between plasma antidiuretic hormone (ADH) concentration and urine osmolality and urine production rate.
In the complete absence of the antidiuretic hormone (ADH; also known as vasopressin), the water permeability of the kidney collecting ducts is very low, allowing for unaltered passage of tubular fluid to become urine. This leads to the production of a large volume (high production rate; red line) of very dilute (low osmolality; blue line) urine. This situation can be brought about by ingesting large volumes of water, which leads to the dilution of plasma solutes (reduced plasma osmolality). Plasma osmolality values less than ~280 mOsm/kg stop ADH release into the bloodstream (see figure). In the presence of maximal concentrations of ADH, the water permeability of kidney collecting ducts is very high due to the fact that ADH stimulates the trafficking of aquaporin-2 (AQP-2) water channels to the apical membrane of collecting duct epithelial cells. This leads to the production of a small volume (low production rate; red line) of very concentrated (high osmolality; blue line) urine. This situation can be brought about by severe dehydration, leading to significantly elevated plasma osmolality levels which, in turn, simulate maximal ADH secretion into the bloodstream (see figure). The human kidney can achieve a minimum urine osmolality of approximately 50 mOsm/kg and a maximum osmolality of approximately 1200 mOsm/kg (see figure). The minimum urine production rate in the presence of maximal concentrations of ADH (antidiuretic urine) is approximately 0.2 mL/min. This is the obligatory urine production rate and is the minimum volume that must be voided in order to adequately rid the body of metabolic waste products. The maximum urine production rate (in the absence of ADH) is about 20 mL/min, which can be achieved after significant water ingestion in healthy individuals with normal kidney function.






Posted: Sunday, November 29, 2015
Last updated: Sunday, November 29, 2015