SHolroydAtWeilCornellMedQatar/Urology/Kidney/Tubules/WaterReabsorption/ControlToWaterIntake

POINT!

With water intake, the plasma osmolarity increases, and negative feedback decreases the water reabsorption.

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 water reabsorption as well as normal plasma and urine osmolarities (isotonic) and urine volume.

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

Step 2: This is in same direction as the plasma osmolarity-decreasing effect of the water reabsorption. Thus, although the strength of the plasma osmolarity-decreasing effect of water reabsorption was adequate before sweating (at baseline), this strength is now too strong (red) to reverse the decreased plasma osmolarity (diluted, hypotonic) produced by water intake. Control by negative feedback is needed.

Step 3: With the strength of the plasma osmolarity-decreasing effect of the water reabsorption before water intake (at baseline) being too strong (red), the negative feedback decreases (blue) the water reabsorption.

Step 4: With the decrease in water reabsorption, concentrated (hypertonic) solution enters the plasma. This will lead to a reverse in the decreased plasma osmolarity (diluted, hyportonic) produced by water intake, increasing it towards normal (baseline, isotonic) osmolarity. Because diluted (hypotonic) solution leaves the tubule due to reabsorption, the fluid remaining in the tubule has increased osmolarity (diluted, hypotonic). Also, with the decrease in water reabsorption, there is more water remaining in the tubule. Overall, the urine becomes diluted and increases in volume.

Challenge Quiz

1.

With water intake, the plasma osmolarity deceases, and negative feedback increases decreases  正解! the water reabsorption from the tubule.

2.

With water intake, the plasma osmolarity increases decreases  正解!. This is in the same direction as opposite direction to  正解! the plasma osmolarity-increasing osmolarity-decreasing  正解! effect of the water reabsorption from the tubule. The negative feedback increases decreases  正解! the water reabsorption from the tubule. This will increase decrease  正解! plasma osmolarity (towards isotonic).

3.

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 water reabsorption. Thus, although the strength of the plasma osmolarity-decreasing effect of water reabsorption 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 increased decreased  正解! plasma osmolarity produced by water intake. The negative feedback increases decreases  正解! water reabsorption from the tubule. Thus, concentrated diluted  正解! solution enters the plasma. This will lead to a reverse 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 an increased a decreased  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 concentrated diluted  正解! and increases decreases  正解! in volume.