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REABSORPTION & SECRETION OF PROXIMAL TUBULE

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REABSORPTION & SECRETION OF PROXIMAL TUBULE

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Q. 1 Which one of the following statements regarding water re-absorption in the tubules is True?
 A The bulk of water re-absorption occurs secondary to Na+ re-absorption
 B

Majority of facultative re-absorption occurs in proximal tubule
 C

Obligatory re-absorption is ADH dependent
 D

20% of water is always re-absorbed irrespective of water balance
Q. 2

The primary active step for sodium reabsorption in the proximal tubule involves:

 A

Sodium-glucose cotransport across the luminal membrane
 B

Sodium/hydrogen ion countertransport across the luminal membrane
 C

Sodium transport via the Na+-K+-ATPase at the basolateral membrane
 D

Sodium-amino acid cotransport across the luminal membrane
Q. 3

Various solutes are reabsorbed in the proximal tubule during tubular reabsorption. Which of the following ion is exchanged for H+ in proximal convoluted tubule?

 A

K+
 B

Na+
 C

HC03
 D

CI-
Q. 4

Reabsorption and secretion of various substances in various quantity is taking place throughout the renal tubules. Minimal reabsorption in kidney occurs for which of the following?

 A

Urea
 B

Glucose
 C

Na
 D

HC03
Q. 5

Water reabsorption in renal tubules varies at different levels. The maximum reabsorption is at:

 A

PCT
 B

Collecting duct
 C

Descending Loop of Henle
 D

Ascending limb of Henle
Q. 6

Which of the following is reabsorbed along with sodium in early portion of proximal tubules?

 A

Glucose
 B

Amino acids
 C

Bicarbonate
 D

All of the above
Q. 7

The highest percentage of glomerular filtrate reabsorption occurs in:

 A

Bowman’s capsule
 B

Proximal tubule
 C

Thick ascending limb of loop of Henle
 D

Distal tubule
Q. 8

Which of the following statements regarding tubular reabsorption is INCORRECT?

 A

It refers to the movement of a substance from the tubular fluid to the peritubular capillary blood
 B

It takes place only in the proximal convoluted tubules
 C

It is important for the conservation of substances important to the body such as Na+, Cl-, glucose, and amino acids
 D

It can occur by active or passive transport mechanisms
Q. 9

Active reabsorption of glucose occurs in the ‑

 A

Distal tubule
 B

Proximal tubule
 C

Loop of henle
 D

Collecting ducts
Q. 10

The main site of bicarbonate reabsorption is:

 A

Proximal convoluted tubule.
 B

Distal convoluted tubule.
 C

Cortical collecting duct.
 D

Medullary collecting duct.
Q. 11

Reabsorption of Water is maximum in:

September 2009, September 2012, March 2013

 A

PCT
 B

DCT
 C

Collecting duct
 D

Loop of henle
Q. 12

Active resorption of sodium ion occurs in:

March 2008

 A

Ascending loop of henle
 B

Early distal tubule
 C

Proximal tubule
 D

All of the above
Q. 13

True about renal secretion—-

 A

Maximum reabsorption in distal tubule
 B

Urea is absorbed 100%
 C

Glucose is reabsorbed in proximal tubule
 D

None
Q. 14

Maximum phosphate is reabsorbed in ‑

 A

PCT
 B

DCT
 C

Loop of Henle
 D

Collecting duct
Q. 1

Which one of the following statements regarding water re-absorption in the tubules is True?

 A

The bulk of water re-absorption occurs secondary to Na+ re-absorption
 B

Majority of facultative re-absorption occurs in proximal tubule
 C

Obligatory re-absorption is ADH dependent
 D

20% of water is always re-absorbed irrespective of water balance
Ans. A
Explanation:

Changes in sodium re-absorption significantly influence the re-absorption of water.

Ref: Textbook of Medical Physiology By Guyton, 10th Edition, Page 299

Q. 2

The primary active step for sodium reabsorption in the proximal tubule involves:

 A

Sodium-glucose cotransport across the luminal membrane
 B

Sodium/hydrogen ion countertransport across the luminal membrane
 C

Sodium transport via the Na+-K+-ATPase at the basolateral membrane
 D

Sodium-amino acid cotransport across the luminal membrane
Ans.
C
Explanation:

Sodium transport via the Na-K-ATPase at the basolateral membrane. This is the only transport step for sodium in the proximal tubule that involves the direct input of energy to move sodium against its electrochemical gradient (in this case from the inside of the cell to the outside).

 

Q. 3

Various solutes are reabsorbed in the proximal tubule during tubular reabsorption. Which of the following ion is exchanged for H+ in proximal convoluted tubule?

 A

K+
 B

Na+
 C

HC03
 D

CI-
Ans.
B
Explanation:

Na+/H+ exchanger (NHE3) is located in the luminal membrane of the proximal tubule epithelial cell.

This transport system allows Na+ to enter the cell from the tubular lumen in exchange for a proton (H+) from inside the cell. 

As in all portions of the nephron, Na+/K+-ATPase in the basolateral membrane pumps the reabsorbed Na+ into the interstitium so as to maintain a low intracellular Na+ concentration. 

The H+ secreted into the lumen combines with bicarbonate (HCO3–) to form H2CO3 (carbonic acid).

Ref: Ives H.E. (2012). Chapter 15. Diuretic Agents. In B.G. Katzung, S.B. Masters, A.J. Trevor (Eds), Basic & Clinical Pharmacology, 12e.

Q. 4

Reabsorption and secretion of various substances in various quantity is taking place throughout the renal tubules. Minimal reabsorption in kidney occurs for which of the following?

 A

Urea
 B

Glucose
 C

Na
 D

HC03
Ans.
A
Explanation:
  • Approximately 66% of filtered sodium ions (Na+), 85% of the NaHCO3, 65% of the K+, 60% of the water, and virtually all of the filtered glucose and amino acids are reabsorbed in the proximal tubule.
  • About half of filtered urea is reabsorbed in the proximal tubule. 
  • An amount equal to that reabsorbed is then secreted back into the loop of Henle. 
  • Finally, about half is reabsorbed again in the medullary collecting duct. The net result is that about half the filtered load is excreted.
 
Ref: Eaton D.C., Pooler J.P. (2009). Chapter 5. Renal Handling of Organic Substances. In D.C. Eaton, J.P. Pooler (Eds), Vander’s Renal Physiology, 7e. 
Q. 5

Water reabsorption in renal tubules varies at different levels. The maximum reabsorption is at:

 A

PCT
 B

Collecting duct
 C

Descending Loop of Henle
 D

Ascending limb of Henle
Ans.
A
Explanation:

Sites of water reabsorption in the kidney:

  • Proximal tubule (65% of the filtered water)
  • Descending thin limb of Henle’s loop (10%)
  • Collecting-duct system (where the fractional reabsorption is the most variable)
 
Ref: Eaton D.C., Pooler J.P. (2009). Chapter 6. Basic Renal Processes for Sodium, Chloride, and Water. In D.C. Eaton, J.P. Pooler (Eds), Vander’s Renal Physiology, 7e.

Q. 6

Which of the following is reabsorbed along with sodium in early portion of proximal tubules?

 A

Glucose
 B

Amino acids
 C

Bicarbonate
 D

All of the above
Ans.
D
Explanation:

Glucose, amino acids, and bicarbonate are reabsorbed along with Na+ in the early portion of the proximal tubule. Glucose is typical of substances removed from the urine by secondary active transport.

 
Also know:
  • Normally about 60% of the filtered Na+ is reabsorbed in the proximal tubule, primarily by Na–H exchange. 
  • Another 30% is absorbed via the Na–2Cl–K cotransporter in the thick ascending limb of the loop of Henle.
Ref: (2012). Chapter 37. Renal Function & Micturition. In Barrett K.E., Boitano S, Barman S.M., Brooks H.L. (Eds), Ganong’s Review of Medical Physiology, 24e.
Q. 7 The highest percentage of glomerular filtrate reabsorption occurs in:
 A

Bowman’s capsule
 B

Proximal tubule
 C

Thick ascending limb of loop of Henle
 D

Distal tubule
Ans.
B
Explanation:

Under all circumstances most of the filtrate is reabsorbed in the proximal tubule. Normally, this reabsorption amounts to about two-thirds of the sodium and water filtered. Normally 60% of Na+ is reabsorbed in the proximal tubule, primarily by Na-H exchange.

Ref: Ganong’s review of Medical Physiology, 23rd Ed, page 648-650

 

Q. 8

Which of the following statements regarding tubular reabsorption is INCORRECT?

 A

It refers to the movement of a substance from the tubular fluid to the peritubular capillary blood
 B

It takes place only in the proximal convoluted tubules
 C

It is important for the conservation of substances important to the body such as Na+, Cl-, glucose, and amino acids
 D

It can occur by active or passive transport mechanisms
Ans.
B
Explanation:
Tubular reabsorption refers to the discrete transfer of substances from the tubular lumen into the peritubular capillaries. It is a highly selective process. In general, the tubules have a high reabsorption capacity for substances needed by the body and little or no reabsorption capacity for substances of no value. The entire sequence of steps involved, in either active or passive reabsorption, is known as transepithelial (“across the epithelium”) transport. The reabsorption of Na+ and Cl- play a major role in body electrolyte and water metabolism. In addition, Na+ transport is coupled to the movement of H+, other electrolytes, glucose, amino acids, organic acids, phosphate and other substances across the tubule walls. 
 
Ref: Cooper C.S., Joudi F.N., Williams R.D. (2010). Chapter 38. Urology. In G.M. Doherty (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.
Q. 9

Active reabsorption of glucose occurs in the ‑

 A

Distal tubule
 B

Proximal tubule
 C

Loop of henle
 D

Collecting ducts
Ans.
B
Explanation:

B i.e. Proximal tubule

Proximal convoluted tubule (early part) reabsorbs almost all of glucose, amino acids, protein, lactate & inorganic phosphate and most (65%) of bicorbonate,Na+,11)0, K+ and CI Q. PCT is also an important site for secretion of organic acids and bases such as oxalate, urate, bile salts, H+ and catecholamines, along with toxins, drugs eg penicillin, salicylates and PAH. So its’ a work horse of nephronQ.

Q. 10

The main site of bicarbonate reabsorption is:

 A

Proximal convoluted tubule.
 B

Distal convoluted tubule.
 C

Cortical collecting duct.
 D

Medullary collecting duct.
Ans.
A
Explanation:

A i.e. Proximal convoluted tubule

About 80 to 90 percent of bicarbonate reabsorption occurs in the proximal tubuleQ.

Segment

% HCO3 reabsorbed

% Na+ reabsorbed

Proximal tubule

80-90%Q

60%Q

Loop of Henle (thick)

10%

30%

Distal tubule & collecting duct.

Remainder

10%
Q. 11

Reabsorption of Water is maximum in:

September 2009, September 2012, March 2013

 A PCT
 B

DCT
 C

Collecting duct
 D

Loop of henle
Ans.
A
Explanation:

Ans. A: PCT

Normally about 65% of the filtered load of sodium and water, essentially all the filtered glucose and amino acids and a slightly lower percentage of filtered chloride are reabsorbed by the proximal tubule.

The proximal tubules also secrete organic acids, bases and hydrogen ions into the tubular lumen.

Q. 12

Active resorption of sodium ion occurs in:

March 2008

 A

Ascending loop of henle
 B

Early distal tubule
 C

Proximal tubule
 D

All of the above
Ans.
D
Explanation:

Ans. D: All of the above

About 65% of the filtered electrolytes are absorbed in PCT actively Thin ascending loop of Henle: Passive diffusion of sodium

Thick ascending loop of Henle: Active transportation of sodium

Early distal tubule: Similar properties as that of thick ascending loop of Henle

Q. 13 True about renal secretion—-
 A

Maximum reabsorption in distal tubule
 B

Urea is absorbed 100%
 C

Glucose is reabsorbed in proximal tubule
 D

None
Ans.
C
Explanation:

Ans. is ‘c’ i.e., Glucose is reabsorbed in proximal tubule

Q. 14

Maximum phosphate is reabsorbed in ‑

 A

PCT
 B

DCT
 C

Loop of Henle
 D

Collecting duct
Ans.
A
Explanation:

Ans. is ‘a’ i.e., PCT

About 60% -70% of filtered phosphate is absorbed in proximal tubule and most of the remaining in distal tubule.