Introduction/NegativeFeedback(MiddleLevel)/CarDownhill

POINT!

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

Before water intake (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.

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

Step 2: This is in the same 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 water intake (at baseline), this strength is now too strong (red) to reverse the low plasma osmolarity (hypotonic plasma) produced by water intake. Control by negative feedback is needed.

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 water intake (at baseline) being too strong (red), the negative feedback decreases (blue) (the synthesis, secretion, and blood concentration of) vasopressin (ADH).

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

Step 5: With the decrease in water reabsorption, concentrated (hypertonic) solution enters the plasma. This increases plasma osmolarity. This will lead to a reverse in the decreased plasma osmolarity from water intake (hypotonic plasma), increasing it towards normal (baseline) osmolarity (isotonic plasma). Because concentrated (hypertonic) solution leaves the tubule due to reabsorption, the fluid remaining in the tubule has a lower osmolarity (hypotonic). Also, with the decrease in water reabsorption, there is more water remaining in the tubule. Overall, the urine becomes more diluted (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, water enters leaves  正解! the plasma and osmolarity increases decreases  正解!. This is in the same direction as opposite direction to  正解! 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 too strong adequate too weak  正解! before water intake (at baseline), this strength is now too strong adequate too weak  正解! to reverse the low plasma osmolarity produced by water intake. The negative feedback increases decreases  正解! (the synthesis, secretion, and blood concentration of) vasopressin (ADH). The water channel-increasing effect of vasopressin (ADH) becomes stronger weaker  正解!, which increases decreases  正解! the number of water channels. With the increases decrease  正解! in water reabsorption by the kidney, concentrated diluted  正解! solution enters the plasma. This increases decreases  正解! plasma osmolarity. This will lead to in the increased decreased  正解! plasma osmolarity from water intake, increasing decreasing  正解! it towards separate from  正解! normal osmolarity. Because concentrated diluted  正解! solution leaves the tubule due to reabsorption, the fluid remaining in the tubule has a higher lower  正解! osmolarity. Also, with the increase decrease  正解! in water reabsorption, there is more less  正解! water remaining in the tubule. Overall, the urine becomes more concentrated diluted  正解! and higher lower  正解! in volume.