05.3 Acid-base balance
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Questions and Answers

What is the primary consequence of uncontrolled acidosis on cellular functions?

  • Increased bicarbonate production
  • Decreased potassium secretion
  • Enhanced renal bicarbonate handling
  • Impaired cellular functions (correct)

Which mechanism reduces tubular pH to 4.5 in the late distal and collecting tubules?

  • Carbonic anhydrase activity increase
  • H⁺-K⁺ ATPase secretion (correct)
  • Na⁺-H⁺ counter-transport
  • Bicarbonate reabsorption enhancement

Which medication class primarily influences acid-base balance through alterations in Na⁺ and K⁺ levels?

  • Diuretics (correct)
  • Beta-blockers
  • ACE inhibitors
  • Calcium channel blockers

What is a key physiological response to manage acidosis concerning bicarbonate production?

<p>Excess H⁺ combining with buffer systems (D)</p> Signup and view all the answers

How is anion gap calculated, and what does it indicate?

<p>[Na⁺] - ([Cl⁻] + [HCO₃⁻]); indicates acid-base disturbance (C)</p> Signup and view all the answers

What characterizes metabolic alkalosis in terms of bicarbonate levels?

<p>Primary increase in HCO₃⁻ (D)</p> Signup and view all the answers

Which type of acidosis is identified by a high anion gap?

<p>Metabolic acidosis (C)</p> Signup and view all the answers

What is a crucial distinguishing factor between metabolic and respiratory causes of acid-base disturbances?

<p>The interpretation of arterial blood gas measurements (D)</p> Signup and view all the answers

How do the kidneys primarily manage extracellular pH?

<p>By secreting hydrogen ions and reabsorbing bicarbonate (A)</p> Signup and view all the answers

What mechanism allows bicarbonate reabsorption in the kidneys?

<p>HCO₃⁻ combines with secreted H⁺ to form H₂CO₃ (A)</p> Signup and view all the answers

Which buffer system is particularly effective in tubular fluid for correcting acidosis?

<p>Phosphate buffer system (C)</p> Signup and view all the answers

During metabolic acidosis, how does the kidney compensate?

<p>By increased hydrogen ion excretion (C)</p> Signup and view all the answers

What is the role of ammonia in renal acid-base balance?

<p>To buffer hydrogen ions during acidosis (C)</p> Signup and view all the answers

What clinical assessment is vital for differentiating acid-base disturbances?

<p>Assess ABG values including pH and anion gap (C)</p> Signup and view all the answers

In which situation might you expect to see increased hydrogen ion excretion?

<p>Metabolic acidosis from gastrointestinal loss (A)</p> Signup and view all the answers

Which of these statements about acidic and basic urine is true?

<p>Acidic urine decreases extracellular base by secreting hydrogen ions (B)</p> Signup and view all the answers

Flashcards

Acidic urine

The kidneys excrete hydrogen ions (H+) in the urine, making it acidic. This reduces excess acid in the body's fluids.

Basic urine

The kidneys can produce urine that contains bicarbonate (HCO3-), making it basic. This helps to remove excess base from the body's fluids.

Hydrogen ion secretion

The kidneys remove hydrogen ions (H+) from the blood and release them into the urine. This process helps maintain a balanced pH in the body.

Bicarbonate reabsorption

Filtered bicarbonate (HCO3-) in the blood is reabsorbed back into the blood. This helps keep bicarbonate levels normal, which is important for pH balance.

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Bicarbonate production

The kidneys can create new bicarbonate (HCO3-) and release it into the blood. This is a crucial mechanism to counter acid build-up in the body.

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Phosphate buffer system

A chemical system in the kidneys that uses phosphate molecules to neutralize excess hydrogen ions (H+).

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Ammonia buffer system

A chemical system in the kidneys that uses ammonia (NH3) to neutralize excess hydrogen ions (H+). This system is vital for managing acidosis.

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Renal compensation for acidosis and alkalosis

Kidneys adjust their bicarbonate reabsorption and hydrogen ion secretion to compensate for changes in blood pH. If the blood is too acidic, they increase bicarbonate reabsorption and hydrogen ion secretion. If the blood is too basic, they do the opposite.

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Kidney Acid-Base Balance

The process by which the kidneys regulate the pH of the blood by balancing the secretion of hydrogen ions (H+) and the reabsorption of bicarbonate (HCO3-), helping maintain a stable internal environment.

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Acidosis

A condition where the pH of the blood is too low, making it acidic. Caused by either an excess of acid or a loss of bicarbonate.

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Alkalosis

A condition where the pH of the blood is too high, making it alkaline. Caused by either a loss of acid or an excess of bicarbonate.

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Hydrogen Secretion Mechanism

A process where carbon dioxide (CO2) diffuses into cells, combines with water to form carbonic acid (H2CO3), and then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). This is the primary mechanism for H+ secretion in the early parts of the kidney.

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Arterial Blood Gas (ABG)

A blood test that measures the pH, partial pressure of carbon dioxide (pCO2), bicarbonate (HCO3-), partial pressure of oxygen (pO2), and anion gap.

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Anion Gap

A measure of the difference between cations (positively charged ions) and anions (negatively charged ions) in the blood. It can help determine the cause of metabolic acidosis.

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Diuretics

A group of medications that increase urine production by inhibiting the reabsorption of sodium in the kidneys. They can indirectly affect acid-base balance by influencing sodium and potassium levels.

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ACE Inhibitors and ARBs

A group of medications that block the action of the angiotensin-converting enzyme (ACE) or angiotensin II receptor blockers (ARBs), reducing blood pressure. They can indirectly influence acid-base balance by affecting sodium reabsorption and altering hydrogen and bicarbonate handling.

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Study Notes

Acid-Base Balance: Renal Control

  • The kidneys regulate extracellular pH by excreting either acidic or basic urine.
  • This process involves hydrogen ion secretion, bicarbonate reabsorption, and bicarbonate generation.
  • Acidic urine decreases extracellular acid, while basic urine removes base.

Renal Hydrogen Ion Secretion

  • Occurs in the renal tubules via counter-transport with sodium.
  • Carbon dioxide (CO2) and water (H2O) form carbonic acid (H2CO3), which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-).

Bicarbonate Reabsorption

  • Filtered bicarbonate combines with secreted hydrogen ions to form carbonic acid (H2CO3).
  • Carbonic acid dissociates into carbon dioxide (CO2) and water (H2O), enabling bicarbonate reabsorption.

Renal Bicarbonate Production

  • Newly generated bicarbonate compensates for losses or increases.

Phosphate Buffer System

  • Phosphate buffers hydrogen ions (H+), particularly effective in tubular fluid due to concentration.

Ammonia Buffer System

  • Ammonia (NH3) and ammonium ions (NH4+) derived from glutamine act as buffers for hydrogen ions, crucial in acidosis.

Clinical Applications

  • Metabolic acidosis (e.g., diarrhea) can lead to low bicarbonate levels, prompting the kidneys to increase hydrogen excretion.
  • ABGs (arterial blood gases) help diagnose metabolic and respiratory acid-base imbalances.
  • Treatment of metabolic acidosis involves bicarbonate reabsorption; respiratory acidosis involves compensatory adjustments in plasma bicarbonate.

Pathophysiology

  • Early tubular segments (proximal tubule, thick ascending limb, early distal tubule) secrete hydrogen ions from carbon dioxide.
  • CO2 diffuses into cells, forming carbonic acid (H2CO3), which then dissociates into hydrogen ions and bicarbonate.
  • Hydrogen ions are secreted via sodium-hydrogen counter-transport (Na-H counter-transport).

Pharmacology

  • Diuretics influence acid-base balance by altering sodium and potassium levels.
  • ACE inhibitors and ARBs decrease angiotensin II, reducing sodium reabsorption, indirectly influencing hydrogen and bicarbonate handling.

Differential Diagnosis

  • Metabolic acidosis is categorized based on anion gap.
  • Respiratory acidosis results from hypoventilation, while metabolic alkalosis results from primary increase in bicarbonate (e.g., vomiting, diuretic use).
  • Respiratory alkalosis occurs due to hyperventilation.

Investigations

  • Arterial blood gases (ABGs) measure pH, pCO2, HCO3, pO2, and anion gap.
  • Anion gap calculation is used to determine metabolic derangements.

Summary and Key Takeaways

  • Kidneys maintain pH balance by controlling hydrogen ion secretion and bicarbonate reabsorption.
  • Phosphate and ammonia buffer systems are vital in managing excess hydrogen ions, particularly in acidosis.
  • Distinguishing metabolic from respiratory acid-base causes is essential for proper diagnosis and treatment.

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Acid-Base Balance PDF Lecture Notes

Description

This quiz explores the renal mechanisms involved in maintaining acid-base balance in the body. Key processes such as hydrogen ion secretion and bicarbonate reabsorption are examined in detail. Test your understanding of how the kidneys regulate extracellular pH through urine composition.

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