SHolroydAtWeilCornellMedQatar/Urology/Kidney/Tubules/WaterReabsorption/ControlToSweating

POINT!

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

narrated video explanation

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

video just after sweating
Step 1: With sweating, water leaves the plasma and osmolarity increases (the plasma becomes hypertonic).

Step 2: With reabsorption (through the water channels, which are increased by vasopressin, ADH), water enters the plasma and osmolarity decreases. This is the opposite effect of sweating. Thus, with the high plasma osmolarity produced by sweating (hypertonic plasma), the baseline strength of the plasma osmolarity-decreasing effect of reabsorption would be too weak. Control by negative feedback is needed.

video just after the increase in vasopressin (ADH) caused by sweating
Step 3: With the baseline effect of the reabsorption (through the water channels, which are increased by vasopressin, ADH) being too weak, the negative feedback increases the synthesis, secretion, and blood concentration of vasopressin (ADH).

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

video showing the changes in plasma and urine after the increase in vasopressin (ADH) caused by sweating
Step 5: The ratio of Na⁺ to water entering the plasma due to reabsorption decreases. This decreases plasma osmolarity. This will lead to a decrease in the increased plasma osmolarity from sweating (hypertonic plasma), returning it towards normal (baseline) osmolarity (isotonic plasma). Because a lower ratio of Na⁺ to water leaves the tubule due to reabsorption, the fluid remaining in the tubule has a higher osmolarity (hypertonic). Also, with an increase in water reabsorption, there is less water remaining in the tubule. Overall, the urine becomes more concentrated (hypertonic) and lower in volume.

Challenge Quiz

1.

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

2.

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

3.

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

4.

With sweating, negative feedback increases decreases  正解! urine volume.

5.

With sweating, negative feedback increases decreases  正解! urine osmolarity.

6.

With sweating, negative feedback increases decreases  正解! plasma osmolarity.

7.

With sweating, 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 the reabsorption would be too weak too strong  正解! prior to control by negative feedback. 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 number of water channels in the kidney causing increased decreased  正解! water reabsorption. Urine osmolarity increases decreases  正解! while volume increases decreases  正解!. This decreases increases  正解! plasma osmolarity, returning to normal separating from normal  正解!.