Acid Base - Pt 2

Question 1

The distal tubule and collecting ducts are responsible for [] the urine.

Answer 1

acidifying

Question 2

The alpha-intercalated cells are the workhouse in the late DCT/CD when it comes to [] H⁺

Answer 2

secreting

Question 3

What 3 types of cells are found in the late DCT/CD that regulate HCO₃^-, H⁺, etc…

Answer 3

Princple Cells

Alpha-intercalated cells

Beta-intercalated cells

Question 4

Alpha-intercalated Cells in the late DCT/CD:

• Primarily in charge of secreting [] []
• 2 specific types of transporters in [] membrane
  
  • [] Pumps (K+/H+-ATPase)
  • H+-[]

Answer 4

• Primarily in charge of secreting acidic H+
• 2 specific types of transporters in apical membrane
  
  • Proton Pumps (K+/H+-ATPase)
  • H+-ATPase

Question 5

Alpha-Intercalated cells in the late DCT/CD:

• HCO₃^- is pumped into the blood through the [] membrane via the [] ([] [] [] []).
  
  • This moves [] into the cell and []out of the cell.

Answer 5

• HCO₃^- is pumped into the blood through the basolateral membrane via the AE2 (Anion Exchanger Type 2).
  
  • This moves Cl^- into the cell and HCO₃^- out of the cell.

Question 6

B-Intercalated cells

• Exist within the [] []
• Secrets [] rather than H⁺ into the tubular fluid
• [] membrane contains [] proteins - anion exchangers.
  
  • These exchangers secrete HCO₃^- while bringing in []
• Only active when blood levels of HCO₃^- are []

Answer 6

• Exist within the collecting duct
• Secrets HCO₃^- rather than H⁺ into the tubular fluid
• Apical membrane contains PENDRIN proteins - anion exchangers.
  
  • These exchangers secrete HCO₃^- while bringing in Cl^-
• Only active when blood levels of HCO₃^- are elevated

Question 7

• B-intercalated cells reabsorb H⁺ by a [] that move hydrogen ions across the [] membrane

Answer 7

B-intercalated cells reabsorb H⁺ by a H+-ATPase that move hydrogen ions across the basal lateral membrane

Question 8

Under normal conditions, [] secretion predominates in the collecting ducts.

Answer 8

Under normal conditions, H⁺ secretion predominates in the collecting ducts.

Question 9

Phosphate Buffer System: Mechanism

• H+ secreted into the tubular lumen combines with [] to form [] which is then exreted
• Since the H+ did not bind with bicarbonate in the tubular lumen, the intracellular [] is reabsorbed and considered to be [] []

Answer 9

• H+ secreted into the tubular lumen combines with HPO₄^2- to form H₂PO₄^- which is then excreted
• Since the H+ did not bind with bicarbonate in the tubular lumen, the intracellular HCO₃^- is reabsorbed and considered to be new bicarbonate

Question 10

Quantitatively, the most important buffer system for the Renal system is the [] []

Answer 10

Quantitatively, the most important buffer system for the Renal system is the NH₄⁺/NH₃​ system

Question 11

Ammonia/Ammonium Formation in PCT

• Filtered glutamine is reabsorbed in [], [], and []
• Glutamine is metabolized in 2 [] and 2 []
• NH₄⁺ can dissociate into [] and [] intracellularly
• [] can freely diffuse across apical membrane, and [] is secreted by [] counter transporters by substituting itself for H⁺
• H⁺ is actively secreted across the apical membrane via the [] as well as being extruded via the [] - which allows H+ to bind with [] in the tubular lumen.

Answer 11

• Filtered glutamine is reabsorbed in PCT, TAL, and early DCT
• Glutamine is metabolized into 2 NH₄⁺ and 2 HCO₃^-
• NH₄⁺ can dissociate into H₊ and NH₃ intracellularly
• NH₃ can freely diffuse across apical membrane, and NH₄⁺ is secreted by NHE3 counter transporters by substituting itself for H⁺
• H⁺ is actively secreted across the apical membrane via the H+-ATPase as well as being extruded via the NHE3 - which allows H+ to bind with NH₃ in the tubular lumen.

Question 12

NH₃ is…

NH₄⁺ is….

Answer 12

NH₃ is…ammonia

NH₄⁺ is….ammonium

Question 13

[] [] or [] [] refers to that fact that NH₄⁺ is not permeable across the apical membrane and therefore becomes trapped int he lumen of the collecting duct

Answer 13

Diffusion Trapping or Ammonia Trapping refers to that fact that NH₄⁺ is not permeable across the apical membrane and therefore becomes trapped int he lumen of the collecting duct

Question 14

For each molecule of NH₄⁺ that is exreted, a molecule of [] is added to the extracelular fluid. Thereby generating a [] [] [] []

Answer 14

For each molecule of NH₄⁺ that is exreted, a molecule of HCO₃^- is added t the extracelular fluid. Thereby generating a net increase in HCO₃^-​​

Question 15

NH₄⁺ can be viewed as an excretion marker of [] [] in the proximal tubule

Answer 15

glutamine metabolism

Question 16

• Increases in extracellular H⁺ stimulates renal [] metabolism
• Increased glutamine metabolism leads to an increase in [] in the tubule and [] in the intersitium.
• Increased NH₄⁺ and HCO₃^- effectively buffer the increased []
• Under “normal” conditions ammonia buffers account for about 50% of the [] [] and 50% of the new [] []

Answer 16

• Increases in extracellular H⁺ stimulates renal glutamine metabolism
• Increased glutamine metabolism leads to an increase in NH₄⁺ in the tubule and HCO₃^- in the intersitium.
• Increased NH₄⁺ and HCO₃^- effectively buffer the increased H⁺
• Under “normal” conditions ammonia buffers account for about 50% of the acid secreted and 50% of the new HCO₃^- formed

Question 17

The kidney is considered to [] [] most changes in the pH…except there is a renal maximum compensation.

Answer 17

completely correct

Question 18

What is the Net Acid Exretion Equation?

What is urinary titrabable acid?

Answer 18

80 mEq/day = (NH₄⁺ Excretion) + ( Urinary Titratable Acid) - (HCO₃^- excretion)

UTA is Free H+

Question 19

Regulation of Renal Tubular H+ Secretion:

• Most important stimuli: Increased []/Decreased [] of ICF
  
  • increases activity of transporters [] H+, increases activty of [], stimulates increase in renal [] synthesis
• Increased Na+ reabsorption Increases [] secretion
• Plasma K⁺ - [], increases H⁺ secretion which leads to a [] alkalosis

Answer 19

• Most important stimuli: Increased H⁺/Decreased pH of ICF
  
  • increases activity of transporters secreting H+, increases activty of glutaminase, stimulates increase in renal ammonia synthesis
• Increased Na⁺ reabsorption Increases H⁺ secretion
• Plasma K⁺ - Hypokalemia, increases H⁺ secretion which leads to a metabolic alkalosis

Question 20

Renal regulation of H+ secretion:

• Increased [] stimualtes H⁺ secretion, resulting in Alkalosis
• Increased Na⁺ reabsorption, leads to a more negative [] [] and promotes [] secretion.
• Also promotes [] secretion by principle cell sof the CD, leading to Hypokalemia

Answer 20

• Increased aldosterone stimulates H⁺ secretion, resulting in Alkalosis
• Increased Na⁺ reabsorption, leads to a more negative intraluminal potential and promotes H⁺ secretion.
• Also promotes K+ secretion by principle cell sof the CD, leading to Hypokalemia

Question 21

Example of Respiratory Alkalosis/Acidosis:

High altitude –> decreased [] –> Stimulates Respiration –> Increases CO₂ [] [] –> Decreases P_CO2 of ECF –> Respiratory []

Answer 21

High altitude –> decreased O₂ –> Stimulates Respiration –> Increases CO₂ Blow off –> Decreases P_CO2​ of ECF –> Respiratory alkalosis