SHolroydAtWeilCornellMedQatar/Endocrinology/VasopressinADH/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

video prior to sweating
Prior to sweating (at baseline), we will make the assumption that the subject is in homeostasis with adequate strength of the plasma osmolarity-decreasing effect of reabsorption (through the water channels, which are increased by vasopressin, ADH) as well as normal plasma and urine osmolarities (isotonic) and urine volume.

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

Step 2: This is in the opposite direction as the plasma osmolarity-decreasing effect of the reabsorption (through the water channels, which are increased by vasopressin, ADH). Thus, although the strength of the plasma osmolarity-decreasing effect of reabsorption (through the water channels, which are increased by vasopressin, ADH) was adequate before sweating (at baseline), this strength is now too weak to reverse the high plasma osmolarity (hypertonic plasma) produced by sweating. Control by negative feedback is needed.

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

Step 4: The water channel-increasing effect of vasopressin (ADH) becomes stronger, which increases 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: With the increase in water reabsorption, diluted (hypotonic) solution enters the plasma. This decreases plasma osmolarity. This will lead to a reverse in the increased plasma osmolarity from sweating (hypertonic plasma), decreasing it towards normal (baseline) osmolarity (isotonic plasma). Because diluted (hypotonic) solution leaves the tubule due to reabsorption, the fluid remaining in the tubule has a higher osmolarity (hypertonic). Also, with the 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!.