Acid Base Balance In The Kidney

Question 1

Normal plasma pH range

Answer 1

7.35 - 7.45

Question 2

What is alkalemia?

Answer 2

Buildup of alkaline substances in body
High pH

Question 3

What is acidemia?

Answer 3

Increase in [H+] in blood
Decreases in pH

Question 4

Impact of alkalemia on Ca2+

Answer 4

• lowers free calcium by causing Ca2+ to come out of solution + bind to albumin
• Ca2+ swaps with H+
• increases neuronal excitability > fire action potentials at small signals
• numbness or tingling + muscle twitching
• paralysis of respiratory muscles if severe

Question 5

Impact of acidemia on Ca2+

Answer 5

• increases free calcium by causing Ca2+ to go into solution (breaks off from albumin)
• affects AP excitability > arrhythmia

Question 6

What are the 3 mechanisms to control pH of blood

Answer 6

Buffers
Ventilation
Renal regulation of H+ and HCO3-

Question 7

Sources of acids in diet

Answer 7

Lipids as fatty acids
Proteins as amino acids

Question 8

How do the kidneys alter pH?

Answer 8

• directly by excreting or reabsorbing H+
• indirectly by changing rates at which HCO3- is reabsorbed or excreted

Question 9

What is the % of H+ output of the lungs and kidneys?

Answer 9

Lungs 75% | rapidly
Kidneys 25% | over a couple days

Question 10

How much HCO3- is aimed to be reabsorbed in the kidney?

Answer 10

100%

Question 11

What are the buffer systems in the PCT?

Answer 11

• Ammonia: NH₃ + H⁺ > NH₄⁺
• Hydrogen phosphate: HPO₄^2- + H+ > H₂PO₄^-
• Glutamine in cell: glutamine > alpha ketoglutarate > 2HCO₃^- reabsorbed | glutamine > 2NH₄⁺ > 2NH₃ + H⁺ > H⁺ back into lumen + NH₃ diffuses back

Question 12

Primary cause of respiratory alkalosis

Answer 12

Excessive artificial ventilation - hyperventilation

Question 13

Compensation of respiratory alkalosis

Answer 13

From renal mechanisms:
- HCO₃^- not reabsorbed in PCT
- late DCT/CD HCO₃^- secreted + H⁺ reabsorbed in intercalating cells

Question 14

Cause of respiratory acidosis

Answer 14

Hypoventilation > CO2 retention

Question 15

Compensation of respiratory acidosis

Answer 15

From renal mechanisms that secrete H⁺ + reabsorb HCO₃^-
- glutamine
- alpha intercalated cells

Question 16

When does metabolic acidosis occur?

Answer 16

• When dietary and metabolic input of H+ exceeds excretion
  lactic acidosis | ketoacidosis
• or when body loses HCO₃^- e..g diarrhoea

Question 17

Causes of metabolic alkalosis

Answer 17

• excessive vomiting of acidic stomach contents
• excessive ingestion of bicarbonate containing antacid

Question 18

Compensation of metabolic alkalosis

Answer 18

Respiratory compensation
- hypoventilation to retain CO2
- this creates more H+ + HCO3-
- restores pH but also makes more bicarbonate

Renal compensation
- HCO3- not reabsorbed in PCT
- late DCT/CD HCO3- secreted + H+ reabsorbed in intercalating cells

Question 19

Compensation of metabolic acidosis

Answer 19

Respiratory compensation
- increases ventilation > CO₂ decreases

Renal compensation
- late DCT/CD secretion of H⁺ + reabsorption of HCO₃^-

Question 20

Compare respiratory and metabolic acidosis in regards to pH, pCO2 and HCO3-

Answer 20

• both pH low
• respiratory acidosis: pCO2 + HCO3- high
• metabolic acidosis: pCO2 normal/low + HCO3- low

Metabolic follows pH change

Question 21

Compare respiratory + metabolic alkalosis in regards to pH, pCO2 and HCO3-

Answer 21

• both pH high
• respiratory acidosis: pCO2 + HCO3- low
• metaboIic acidosis: pCO2 normal/high + HCO3- high

Metabolic follows pH change

Question 22

Outline the action of glutamine in the PCT

Answer 22

• becomes aKG (alpha ketoglutamate) > 2HCO3- > reabsorbed into blood with Na+
• becomes 2NH4+ > NH3 + H+ > H+ back into lumen swapped with Na2+ | NH3 diffuses back

Question 23

What is the anion gap?

Answer 23

Difference between the concentrations of cations and anions in the body due to anions that are not measured

Question 24

Equation for the anion gap

Answer 24

([Na+] + [K+]) - ([Cl-] +[HCO3-])

Question 25

When does the anion gap increased?

Answer 25

If HCO3- is replaced by other anions e.g. lactic acid

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