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Sem3: PHYS30240 GI and Renal Physiology > L13 Renal Contribution to Acid/Base Ballance > Flashcards

L13 Renal Contribution to Acid/Base Ballance Flashcards

1
Q

What is acid derived from the hydration of CO2 called?

How is it eliminated?

A

Volatile Acid

Eliminated Via the Lungs

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2
Q

What is acid derived from the protein metabolism and dietary intake of Sulfates/phosphates called?

How is it eliminated?

A

Non-Volatile Acid

Kidneys

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3
Q

In order to maintain acid-base balance, the kidney must accomplish what two tasks?

A

1) Reabsorption of all filtered bicarbonate

2) Excrete the daily non-volatile acid (not derived from hydration of CO2)

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4
Q

How is H+ Excreted?

A

Hydrogen Ion Secretion: H+ is buffered in the blood, NOT filtered by kidneys as free ions

In the Tubular Fluid Secreted H+:

  • Combine with filtered bicarbonate => Bicarbonate Reabsorption
  • Combine with urinary buffers to be excreted as ((Titratable Acids and Ammonium**
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5
Q

Segmental Reabsorption of HCO3?

A
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6
Q

What renal mechanisms come into play to bring pH back to normal when [H+] is elevated?

A
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7
Q

Cellular Mechanisms for Proximal Tubule H+ and HCO3 Transport?

A

H+ secretion across apical membrane:

  • Primarily via a Na+/H+ antiporter (NHE_3)_
  • Via H+ ATPase

Carbonic Anhydrase (CA) plays important role in H+ secretion/HCO3 reabsorption

  • Within cells, Carbonic Anhydrase 2 generates H+ and HCO3 from CO2 and H20
  • Membrane bound Carbonic Anhydrase 4 produces H20 and CO2 from luminal carbonic acid (H2CO3)

Exit of HCO3 across basolateral membrane:

  • Primarily via a Na+/3HCO3 Symporter (NBC1)
  • Also via a Cl-/HCO3-antiporter (AE2)
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8
Q

How do Cellular Mechanisms for H+/HCO3 transport by TAL and Early DCT differ from the PCT?

A

PCT

  • H+ secretion across apical membrane occurs primarily via a Na+/H+ antiporter (NHE 3) and via H+-ATPase
  • HCO3-reabsorption across basolateral membrane occurs primarily via a Na+/ 3 HCO3-symporter (NBC1) and via a Cl-/HCO3-antiporter

TAL and Early DCT

  • H+ secretion across apical membrane occurs primarily via a Na+/H+ antiporter (NHE 2) and via H+-ATPase
  • HCO3-reabsorption across basolateral membrane occurs primarily via a Na+/HCO3-symporter (NBC n 1) and via a Cl-/HCO3-antiporter
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9
Q

Type A intercalated cells secrete ____and reabsorb ______

Type B intercalated cells secrete _____ and reabsorb _____

Activity of Type A cells increases when blood _______; activity of Type B cells increases if blood _________

A

Type A intercalated cells secrete H+ and reabsorb HCO3-

Type B intercalated cells secrete HCO3- and reabsorb H+

Activity of Type A cells (A= ACID) increases when blood academic; activity of Type B (B= BASE) cells increases if blood alkalemia

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10
Q

Cellular Mechanisms for H+ and HCO3 Secretion by Type A Intercalated Cells of the Collecting Duct

A

H+ secretion across apical membrane occurs by H+/K+ ATPase and H+/ATPase

HCO3-reabsorption across basolateral membrane occurs via a Cl-/HCO3-antiporter (AE-1)

No Na+, K+/ATPase pumps on basolateral side: energy required for transport function of these cells is derived from H+ gradient generated by H+-ATPases on apical side

Aldosterone stimulates H+ ATPase Activity

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11
Q

Cellular Mechanisms for H+ and HCO3 Secretion by Type B Intercalated Cells of the Collecting Duct

A

H+/HCO3-secretion across apical membrane occurs via Cl-/HCO3-antiporter (Pendrin)

H+ reabsorption across basolateral membrane occurs via ((H+/ATPase((

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12
Q

Titratable Acid vs Ammonium?

A

A titratable acid refers to any acid that can lose proton(s) in an acid-base reaction

In renal physiology, a titratable acid is a term that refers to non-volatile acids (i.e. phosphoric acid, sulfuric acid) and is used to explicitly exclude ammonium (NH4+)

Ammonium is not measured as part of the titratable acidity because the high pK (pK=9) of ammonium means no H+ is removed from NH4+ during titration to a pH of 7.4

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13
Q

Mechanisms by which tubules add additional HCO3- to plasma?

A

Reabsorption of filtered HCO3-alone cannot replenish the HCO3-lost during acid neutralization

  • PCT production/secretion of Ammonium (NH4+) (Ammonigenesis)- (quantitatively more important): => H+ is excreted, HCO3-is added to the plasma
  • In collecting tubule Type A intercallated cells secrete H+ which in the lumen with a buffer other than HCO3- (HPO42-, creatinine, uric acid) => production of “additional” HCO3-for the plasma as CA2 intracellular is able to generate more HCO3
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14
Q

Overall scheme of renal NH3/NH4+ Handling?

Key Point 1: Significant proportion of the NH4+ secreted by _______ is reabsorbed by ____ => ultimately excreted

Key Point 2: NH4+ excretion is ___________ in acidosis

A

Key Point 1: Significant proportion of the NH4+ secreted by PCT is reabsorbed by TAL => ultimately excreted

Key Point 2: NH4+ excretion is INCREASED in acidosis

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15
Q

__________ stimulates phosphaturia because phosphate serves as a titratable acid buffer. By contrast, __________ increases renal phosphate absorption

A

Acidosis stimulates phosphaturia because phosphate serves as a titratable acid. By contrast, alkalosis increases renal phosphate absorption

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16
Q

Summary of renal production/secretion of ammonium

  • NH4+ is formed by the ___________ from __________
  • ________ can readily diffuse through membranes, however, protonated _______ becomes trapped in the tubular lumen and can be excreted
  • Much of secreted NH4+ is reabsorbed by the ______ => accumulation of NH4+ in medullary interstitium
  • NH4+ in the medullary interstitium dissociates to ______ and ________ => diffuses into the collecting duct lumen (concentration gradient), again trapped due to protonation
  • Thus, H+ secretion by collecting duct is critical for excretion of ________ and reabsorption of _______
A

Summary of renal production/secretion of ammonium

  • NH4+ is formed by the proximal tubule from glutamine
  • NH3 can readily diffuse through membranes, however, protonated NH4+ becomes trapped in the tubular lumen and can be excreted
  • Much of secreted NH4+ is reabsorbed by the TAL => accumulation of NH4+ in medullary interstitium
  • NH4+ in the medullary interstitium dissociates to H+ and NH3 => diffuses into the collecting duct lumen (concentration gradient), again trapped due to protonation
  • Thus, H+ secretion by collecting duct is critical for excretion of NH4+ and reabsorption of HCO3-
17
Q

Renal responses to Acidosis

  • Sufficient H+ ions secreted to reabsorb all filtered ________
  • Still more H+ ions secreted, and this contributes additional HCO3-to the plasma as these H+ ions are excreted bound to _______________________________
  • Tubular glutamine metabolism and ammonium excretion are _____________, further contributing HCO3- to plasma

Net result: More new HCO3- than usual added to blood, plasma HCO3-is increased, thereby compensating for the acidosis. The urine is highly acidic (lowest attainable pH = _____)

A

Renal responses to Acidosis

  • Sufficient H+ ions secreted to reabsorb all filtered HCO3-
  • Still more H+ ions secreted, and this contributes additional HCO3-to the plasma as these H+ ions are excreted bound to non-bicarbonate urinary buffers (i.e. HPO42-)
  • Tubular glutamine metabolism and ammonium excretion are INCREASED, further contributing HCO3- to plasma

Net result: More new HCO3- than usual added to blood, plasma HCO3-is increased, thereby compensating for the acidosis. The urine is highly acidic (lowest attainable pH = 4.4)

18
Q

Renal Responses to Alkalosis

  • Reduced H+ => Significant amounts of HCO3-excreted in urine
  • Little to no excretion of H+ ions on non-bicarbonate urinary buffers
  • DECREASED tubular glutamine metabolism and ammonium excretion => little/no new HCO3- contributed to plasma.
A
  • Reduced H+ => Significant amounts of HCO3-excreted in urine
  • Little to no excretion of H+ ions on non-bicarbonate urinary buffers
  • DECREASED tubular glutamine metabolism and ammonium excretion => little/no new HCO3- contributed to plasma.
18
Q

Renal Responses to Alkalosis

  • Reduced H+ => Significant amounts of ___________excreted in urine
  • Little to no excretion of H+ ions on __________________
  • ________ tubular glutamine metabolism and ammonium excretion => little/no new HCO3- contributed to plasma.
A
  • Reduced H+ => Significant amounts of HCO3- excreted in urine
  • Little to no excretion of H+ ions on non-bicarbonate urinary buffers
  • DECREASED tubular glutamine metabolism and ammonium excretion => little/no new HCO3- contributed to plasma.
19
Q

Renal contribution to acid-base regulation=_________ + _________- _____________

A

Renal contribution to acid-base regulation= Titratable acid excreted + NH4 Excreted - HC03 Excreted

Sem3: PHYS30240 GI and Renal Physiology (24 decks)

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