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Questions and Answers
What effect does an increase in pH from 7.4 to 7.6 have on [H+]?
What effect does an increase in pH from 7.4 to 7.6 have on [H+]?
How much does [H+] increase when pH decreases from 7.4 to 7.2?
How much does [H+] increase when pH decreases from 7.4 to 7.2?
In which range does a given change in pH reflect a larger change in [H+]?
In which range does a given change in pH reflect a larger change in [H+]?
Which type of acid is produced from protein catabolism?
Which type of acid is produced from protein catabolism?
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What is the role of carbonic anhydrase in acid-base balance?
What is the role of carbonic anhydrase in acid-base balance?
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What substance is eliminated by the kidneys in acid-base balance?
What substance is eliminated by the kidneys in acid-base balance?
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What condition could lead to the formation of β-hydroxy butyric acid in the body?
What condition could lead to the formation of β-hydroxy butyric acid in the body?
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Which of the following body fluids has a pH of 8.0?
Which of the following body fluids has a pH of 8.0?
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What effect does increased bicarbonate or decreased PCO2 have on the body's pH levels?
What effect does increased bicarbonate or decreased PCO2 have on the body's pH levels?
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Which mechanism primarily stabilizes plasma bicarbonate within the kidneys?
Which mechanism primarily stabilizes plasma bicarbonate within the kidneys?
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During metabolic alkalosis, what physiological change is most likely to occur?
During metabolic alkalosis, what physiological change is most likely to occur?
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What role does aldosterone play in the secretion of H+ ions in the kidneys?
What role does aldosterone play in the secretion of H+ ions in the kidneys?
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What is the primary regulator of ventilation that affects the acid/base balance?
What is the primary regulator of ventilation that affects the acid/base balance?
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What is the primary mechanism through which titratable acidity is achieved in renal processes?
What is the primary mechanism through which titratable acidity is achieved in renal processes?
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In the presence of acidosis, what is the expected renal response regarding bicarbonate?
In the presence of acidosis, what is the expected renal response regarding bicarbonate?
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How do buffer systems function in response to acid-base disturbances?
How do buffer systems function in response to acid-base disturbances?
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What triggers the secretion of H+ in the renal system?
What triggers the secretion of H+ in the renal system?
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How does the renal system compensate for HCO3- deficits generated by metabolism?
How does the renal system compensate for HCO3- deficits generated by metabolism?
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Which mechanism is primarily responsible for urine buffering through titratable acidity?
Which mechanism is primarily responsible for urine buffering through titratable acidity?
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What is the effect of aldosterone on H+ secretion in the renal system?
What is the effect of aldosterone on H+ secretion in the renal system?
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What happens to luminal pH when HCO3- is completely neutralized in the nephron?
What happens to luminal pH when HCO3- is completely neutralized in the nephron?
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How does the secretion of H+ as NH4+ occur in the proximal tubule?
How does the secretion of H+ as NH4+ occur in the proximal tubule?
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What is the primary role of the kidneys in response to the secretion of non-volatile acids?
What is the primary role of the kidneys in response to the secretion of non-volatile acids?
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What is the consequence of plasma alkalosis on H+ secretion?
What is the consequence of plasma alkalosis on H+ secretion?
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Study Notes
Renal Control of Bicarbonate
- 99.9% of the filtered bicarbonate (HCO3-) is neutralized in the nephron, primarily in the proximal tubule
- For every HCO3- neutralized in the tubule, one HCO3- is released into the peritubular capillaries
- Once HCO3- is removed from the filtrate, the luminal pH falls, reaching as low as 4.5
- The pH gradient from 7.4 (normal) to 4.5 is about 1000-fold
- Plasma acidosis promotes H+ secretion, while plasma alkalosis decreases H+ secretion
Repairing Plasma HCO3- Deficits
- Non-volatile acids (like sulfuric and phosphoric acid) are liberated by metabolism
- HCO3- deficit is repaired by the kidneys, releasing more HCO3- into the peritubular capillary blood than present in the filtrate
- New HCO3- synthesis in tubule cells requires secretion of H+ beyond filtered HCO3-
- Additional H+ is unloaded using phosphate and ammonium (NH4+) as buffers due to the limited pH drop in tubular fluid (maximum 4.5)
Titratable Acidity for Urine Buffering
- This is primarily filtered phosphate (also lactate, acetoacetate, etc.)
- Phosphate's pK (6.8) is ideal for buffering urine
- H+ binding to phosphate allows for additional HCO3- synthesis
- Aldosterone stimulates H+ secretion into the lumen via the H+/ATPase in intercalated cells of the cortical collecting tubules
Mechanism of Excretion of H+ as NH4+
- The proximal tubule metabolizes glutamine from blood to yield NH3 and α-ketoglutarate
- Highly diffusible NH3 enters the tubular fluid
- NH3 is protonated in the lumen, becoming NH4+
- This H+ secretion as NH4+ is known as diffusion trapping
- α-ketoglutarate is metabolized to HCO3-
- Each glutamine molecule yields two HCO3- (to blood) and two NH4+ (lost in urine)
pH and H+ Concentrations of Body Fluids
- Normal plasma pH is 7.4, corresponding to an H+ concentration of 4 x 10-8 mol/L (0.00004 mEq/L)
- Extreme acidosis can lower pH to 7.0 with an H+ concentration of 1 x 10-7 mol/L (0.0001 mEq/L)
- Extreme alkalosis can raise pH to 7.7 with an H+ concentration of 2 x 10-8 mol/L (0.00002 mEq/L)
- Maximum urine acidity is pH 4.5, with an H+ concentration of 3 x 10-5 mol/L (0.03 mEq/L)
- Gastric HCl has a pH of 0.8, with an H+ concentration of 0.15 mol/L (150 mEq/L)
Types of H+ in the Body
- Volatile acid (eliminated by lungs): CO2 produced from aerobic metabolism
- Non-volatile or fixed acids (eliminated by kidneys): sulfuric acid (from protein catabolism)
- Non-volatile or fixed acids (eliminated by kidneys): phosphoric acid (from phospholipid catabolism)
- Non-volatile or fixed acids (eliminated by kidneys): additional acid loads from exercise (lactate), diabetic ketosis (β-hydroxy butyric and acetoacetic acids), and poison ingestion (salicylic acid, glycolic acid)
Buffers and How They Work
- Buffers minimize pH changes but cannot return pH to normal
- The important buffer system in the blood is the bicarbonate buffer system:
- Normal plasma bicarbonate concentration is 24 mEq/L
- Normal PCO2 is 40 mmHg
- This gives a bicarbonate/CO2 ratio of 20:1
- Decreased bicarbonate or increased PCO2 leads to acidosis
- Increased bicarbonate or decreased PCO2 leads to alkalosis
Acid-Base Map and Acid-Base Balance
- Isohydric lines on the acid-base map represent constant pH
- One can maintain the same pH by changing both PCO2 and [HCO3-]
- The ellipse on the acid-base map represents the normal pH range
Renal/Respiratory Compensation
- Lungs and kidneys regulate CO2 and HCO3-, respectively, to maintain the ratio of [HCO3-] to dissolved CO2 near 20
- This regulation is called compensation, which helps to restore pH to normal following an acid/base disturbance
Acid/Base Functions of the Lungs
- Lungs exchange CO2 and O2, regulating PaCO2 and PaO2 within narrow limits via respiratory control mechanisms
- PaCO2 is the primary regulator of ventilation, crucial for acid-base balance and affected by hyperventilation and hypoventilation
Renal Control of Bicarbonate
- Kidneys stabilize plasma [HCO3-] (22-26 mEq/L) by:
- Complete recovery of filtered bicarbonate when [HCO3-]plasma is below 26 mEq/L
- Synthesis of new HCO3- beyond that entering the glomerular filtrate
- Excretion of excess HCO3- (above 26 mEq/L) in urine
- Reabsorption of HCO3- is saturated at 40 mEq/L
Mechanism of HCO3- Recovery
- H+ secretion drives this process
- H+ is formed in the intracellular fluid via the reaction of CO2 and water catalyzed by carbonic anhydrase
- H+ is exchanged for Na+ (proximal tubule) or actively secreted (distal tubule)
- ATII directly stimulates Na+ exchange in the proximal tubule
- HCO3- enters the peritubular capillary blood
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Description
This quiz focuses on the renal mechanisms involved in bicarbonate (HCO3-) control, including its neutralization in the nephron and the repair of plasma HCO3- deficits. It explores the impact of pH changes and the role of non-volatile acids in renal function. Test your understanding of these critical processes in maintaining acid-base balance in the body.
