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Renal Functions, Basic Processes, and Anatomy

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Chloride reabsorption parallels sodium reabsorption mainly because

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a. chloride is almost always transported via a symporter with sodium.

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b. chloride is the most abundant negatively charged species available to balance the reabsorption of the positive charge on sodium.

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c. chloride has such a high passive permeability.

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d. chloride and sodium are both part of the sodium chloride molecule and cannot be separated.

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(b) Reabsorbed sodium must be balanced by reabsorbed anions. Once most of the bicarbonate is reabsorbed, only chloride exists in high enough concentration to match the continued reabsorption of sodium.

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The obligatory water loss in the kidney

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a. is another name for insensible loss of water.

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b. occurs because there is always at least some excretion of waste solutes.

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c. occurs because there is an upper limit to how fast aquaporins can reabsorb water.

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d. is the amount of water that accompanies salt excretion.

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(b) So long as there is filtration there is excretion of organic waste, which obligates water to be excreted also.

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Which region of the tubule secretes water?

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a. The descending thin limb.

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b. The cortical collecting duct.

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c. The medullary collecting duct (when ADH is absent).

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d. No region secretes water.

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(d) Osmotic conditions in all tubule regions favor water reabsorption.

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If the thick ascending limb stopped reabsorbing sodium, then the final urine would be

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a. iso-osmotic with plasma in all conditions.

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b. dilute.

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c. concentrated.

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d. dilute or concentrated, depending on ADH.

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(a) The tubular fluid entering the medulla is iso-osmotic. If the tubules did not separate salt from water, the medullary interstitium would remain iso-osmotic. The luminal fluid would also remain iso-osmotic because there would be no tendency to either dilute it or concentrate it.

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If a healthy young person drinks a large amount of water, which of the following is unlikely to happen?

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a. An increase in medullary blood ...

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