Renal Regulation Of Acid-Base Balance

RENAL REGULATION OF ACID-BASE BALANCE

Q. 1

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. 1

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. 2

Bicarbonate is maximally absorbed in which part of the nephron?

 A

PCT

 B

DCT

 C

Thick ascending loop of Henle

 D

Collecting duct

Q. 2

Bicarbonate is maximally absorbed in which part of the nephron?

 A

PCT

 B

DCT

 C

Thick ascending loop of Henle

 D

Collecting duct

Ans. A

Explanation:

80-90% of bicarbonate reabsorption occurs in the PCT. The secreted H+ ion combines with filtered HCO3– to form H2CO3 and the presence of carbonic anhydrase on the apical membrane of the proximal tubule catalyzes the formation of H2O and CO2 from H2CO3. The apical membrane of epithelial cells lining the proximal tubule is permeable to CO2 and H2O, and they enter the tubule rapidly. Eighty per cent of the filtered load of HCO3– is reabsorbed in the proximal tubule. The cells of the proximal tubule are also involved in vitamin D hydroxylation.

Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 39. Acidification of the Urine & Bicarbonate Excretion. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.


Q. 3

The main site of bicarbonate reabsorption is:

 A

Proximal convoluted tubule.

 B

Distal convoluted tubule.

 C

Cortical collecting duct.

 D

Medullary collecting duct.

Q. 3

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. 4

Following are true about HCO3-except:

 A

Extracellular concentration 25 m mol

 B

Intracellular concentration 10 m mol

 C

7.5% solution gives 2 nmols

 D

In kidney, HCO3- is produced by carbonic anhydrase

Q. 4

Following are true about HCO3-except:

 A

Extracellular concentration 25 m mol

 B

Intracellular concentration 10 m mol

 C

7.5% solution gives 2 nmols

 D

In kidney, HCO3- is produced by carbonic anhydrase

Ans. C

Explanation:

C i.e. 7.5% solution gives 2n mols

  • Concentration of bicarbonate

– Intracellular : 10 mmoVLQ

Extracellular : 27 mmol/LQ

In kidney bicarbonate is produced by carbonic anhydraseQ.


Q. 5

PCT absorbs all except: 

September 2008

 A

Sodium

 B

Amino acids

 C

Glucose

 D

Hydrogen ions

Q. 5

PCT absorbs all except: 

September 2008

 A

Sodium

 B

Amino acids

 C

Glucose

 D

Hydrogen ions

Ans. D

Explanation:

Ans. D: Hydrogen ions

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 secretes organic acids, bases and hydrogen ions into the tubular lumen.

 


Q. 6

Hydrogen ion is eliminated by:            

September 2005

 A

Kidney

 B

Lungs

 C

Liver

 D

Stomach

Q. 6

Hydrogen ion is eliminated by:            

September 2005

 A

Kidney

 B

Lungs

 C

Liver

 D

Stomach

Ans. A

Explanation:

Ans. A: Kidney

Cells of proximal and distal tubules secrete hydrogen ions which comes from carbonic acid For each hydrogen ion secreted, one sodium ion and one bicarbonate ion enters the interstitial fluid.


Q. 7

Collecting duct has which cells ‑

 A

Principle and intercalated

 B

Parietal and oxyntic

 C

Lacis cells

 D

Podocytes

Q. 7

Collecting duct has which cells ‑

 A

Principle and intercalated

 B

Parietal and oxyntic

 C

Lacis cells

 D

Podocytes

Ans. A

Explanation:

Ans. is ‘a’ i.e., Principle and intercalated

Collecting duct is 20 mm long and pass through the renal cortex and medulla to empty into the pelvis of the kidney at the apex of the medullary pyramids. The epithelium of the collecting ducts is made up of two types of cell

i)  Principal cells (P cells), which are involved in Na+ reabsorption and ADH stimulated water reabsorption.

ii) Intercalated cells (I cells) which are concerned with acid (H+) secretion and HCO3– transport.



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