Equation [4] indicates that the free water clearance will be greater than zero whenever the urine osmolality is less than the plasma osmolality. In other words, whenever the urine is dilute compared with the plasma, free water is being lost from the body and the plasma is being concentrated. On the other hand, whenever the urine osmolality is greater than the plasma osmolality, the free water clearance becomes negative. A negative free water clearance indicates that relatively more solute than water is being excreted and that water is being conserved and returned to the plasma. The negative free water clearance is sometimes given by a different symbol, TCH2O; however, there is little justification for this additional term and it is simpler to refer to a negative CH2O as indicating urinary concentration.

As described earlier, when the kidneys are excreting hypo-osmotic urine, the plasma is being concentrated. On the other hand, when hyperosmotic urine is being excreted, the kidneys are effectively diluting the plasma. To understand this more fully, the mass balance relations involved in urinary dilution and concentration are shown in the following examples. The few minutes spent working out and understanding the calculations in each example will be rewarding in appreciating the concentrating and diluting capacity of the kidneys.

From these two examples, it can be seen that the kidney is more effective in clearing free water from the plasma than in concentrating the urine and conserving water. The maximal rate of free water clearance can be as high as 10-12 mL/min in a maximal water diuresis. On the other hand, with maximal vasopressin levels, free water clearance can become only as negative as about 2.0 mL/min. The human kidney is less able to conserve water than are the kidneys of many other mammals. For example, desert animals can develop urine osmolalities up to 5000 mOsm/kg H2O, and certain desert rats in Australia can develop urine osmolalities of 9000 mOsm/ kg H2O!

Get Rid of Gallstones Naturally

Get Rid of Gallstones Naturally

One of the main home remedies that you need to follow to prevent gallstones is a healthy lifestyle. You need to maintain a healthy body weight to prevent gallstones. The following are the best home remedies that will help you to treat and prevent gallstones.

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