SHolroydAtWeilCornellMedQatar/Urology/Kidney/Tubules/WaterChannels/ControlToWaterIntake

POINT!

With water intake, the plasma osmolarity decreases and negative feedback decreases the synthesis, secretion, and blood concentration of vasopressin (anti-diuretic hormone, ADH).

Prior to water intake (at baseline), we will make the assumption that the subject is in homeostasis with normal plasma and urine osmolarities (isotonic) and volumes.

Step 1: With water intake, water enters the plasma and osmolarity decreases (the plasma becomes hypotonic).

Step 2: With reabsorption (through the water channels, which are increased by vasopressin, ADH, water enters the plasma and osmolarity decreases. This the same effect as water intake. Thus, with the low plasma osmolarity produced by water intake (hypotonic plasma), the baseline strength of the plasma osmolarity-decreasing effect of reabsorption would be too strong. Control by negative feedback is needed.

Step 3: With the baseline effect of the reabsorption (through the water channels, which are increased by vasopressin, ADH) being too strong, the negative feedback decreases the synthesis, secretion, and blood concentration of vasopressin (ADH).

Step 4: The water channel-increasing effect of vasopressin (ADH) decreases, thereby decreasing the number of water channels. This decreases the reabsorption of water by the kidney.

Step 5: The ratio of Na⁺ to water entering the plasma due to reabsorption increases. This increases plasma osmolarity. This will lead to an increase in the decreased plasma osmolarity from water intake (hypotonic plasma), returning it towards normal (baseline) osmolarity (isotonic plasma). Because a higher ratio of Na⁺ to water leaves the tubule due to reabsorption, the fluid remaining in the tubule has a lower osmolarity (hypotonic). Also, with a decrease in water reabsorption, there is more water remaining in the tubule. Overall, the urine becomes less concentrated (hypotonic) and higher in volume.

Challenge Quiz

1.

With water intake, negative feedback increases decreases  正解! the synthesis, secretion, and blood concentration of vasopressin (anti-diuretic hormone, ADH).

2.

With water intake, negative feedback increases decreases  正解! the number of water channels in the kidney.

3.

With water intake, negative feedback increases decreases  正解! water reabsorption by the kidney.

4.

With water intake, negative feedback increases decreases  正解! urine volume.

5.

With water intake, negative feedback increases decreases  正解! urine osmolarity.

6.

With water intake, negative feedback increases decreases  正解! plasma osmolarity.

7.

With water intake, the plasma osmolarity decreases increases  正解!. The effect would be the same as opposite to  正解! that of reabsorption of water by the kidney, which decreases increases  正解! plasma osmolarity. The effect of reabsorption would be too little too much  正解!. Negative feedback increases decreases  正解! the synthesis, secretion, and blood concentration of vasopressin (anti-diuretic hormone, ADH). This in turn increases decreases  正解! the production of water channels in the kidney causing increased decreased  正解! water reabsorption. Urine osmolarity will increase decrease  正解! while volume will increase decrease  正解!. This will decrease increase  正解! plasma osmolarity, returning to normal separating from normal  正解!.