Metabolic Alkalosis and Renal Compensation

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Questions and Answers

What happens to bicarbonate reabsorption from tubules during raised pCO2 levels?

More HCO3– are reabsorbed from the tubules in response to raised pCO2 levels.

How is metabolic alkalosis defined biochemically?

Metabolic alkalosis is characterized by an absolute or relative increase in [HCO3–].

What biochemical changes occur during uncompensated metabolic disorders?

There is a disproportionate increase in [H2CO3], along with increased [HCO3–] and total CO2 content.

What role do kidneys play in response to increased pCO2?

The kidneys reabsorb more HCO3– to manage elevated pCO2 levels. Signup and view all the answers

Identify a condition that can cause suppression of respiration affecting CO2 levels.

Brain damage due to trauma is one condition that can suppress respiration. Signup and view all the answers

What happens to urinary NH3 and titratable acidity in compensated metabolic alkalosis?

Urinary NH3 and titratable acidity are both increased. Signup and view all the answers

How does metabolic alkalosis affect the respiratory center (RC)?

Metabolic alkalosis inhibits the respiratory center, leading to shallow and irregular breathing. Signup and view all the answers

What is the primary cause of clinically observed metabolic alkalosis?

The primary cause is an increase in the 'alkali reserve' or excess HCO3–. Signup and view all the answers

What is the effect of decreased ventilation on pCO2 and respiratory compensation?

Decreased ventilation raises pCO2, which stimulates respiratory compensation. Signup and view all the answers

What happens to cation and HCO3– excretion during renal compensation?

Cation and HCO3– excretion increase due to decreased H+-Na+ exchange. Signup and view all the answers

List one compensatory mechanism in response to alkalosis.

Increased alkali excretion is one compensatory mechanism. Signup and view all the answers

How does alkalosis affect urinary acidity?

Urinary acidity decreases and there is a decrease in NH3 formation. Signup and view all the answers

What biochemical changes occur in hypokalaemia during alkalosis?

Increased excretion of K+ can lead to K+ depletion or hypokalaemia. Signup and view all the answers

What characterizes uncompensated metabolic alkalosis biochemically?

It is characterized by disproportionate increases in [HCO3–], pCO2, and total CO2 content. Signup and view all the answers

What occurs in fully compensated metabolic alkalosis regarding [HCO3–] and [H2CO3]?

In fully compensated alkalosis, [HCO3–] and [H2CO3] increase proportionately. Signup and view all the answers

Describe the urinary findings in fully compensated metabolic alkalosis.

Decreases in urinary NH3 and titratable acidity are observed. Signup and view all the answers

What causes metabolic acidosis?

Metabolic acidosis is caused by a reduction in plasma HCO3– leading to a decrease in the pH. Signup and view all the answers

Describe the role of the respiratory center in the primary compensatory mechanism for acidosis.

The respiratory center is stimulated by acidosis, causing deep and rapid breathing to increase ventilation and reduce CO2 levels. Signup and view all the answers

What is the ratio of [HCO3–] to [H2CO3] during metabolic acidosis?

The ratio is decreased from the normal 20:1. Signup and view all the answers

What happens to pCO2 during the primary compensatory mechanism for acidosis?

pCO2 levels decrease due to increased ventilation. Signup and view all the answers

In uncompensated acidosis, what happens to the concentration of H+ ions?

The concentration of H+ ions in the blood increases. Signup and view all the answers

What renal mechanisms are employed during compensatory responses to metabolic acidosis?

Renal mechanisms include conserving cations, increasing NH3 formation, H+ excretion, and HCO3– reabsorption. Signup and view all the answers

What is the difference between compensated and uncompensated phases of acid-base imbalance?

In compensated phase, the body actively corrects the imbalance, while in uncompensated phase, these compensatory mechanisms fail. Signup and view all the answers

Explain the two opposing forces in respiratory compensation during acidosis.

Acidosis stimulates the respiratory center while low pCO2 depresses it, creating a partial compensatory effect. Signup and view all the answers

What are the biochemically characteristic changes in uncompensated metabolic alkalosis?

In uncompensated metabolic alkalosis, there is a disproportionate decrease in [H2CO3] and pCO2, a decrease in [HCO3–], a decrease in CO2 content, an increase in the [HCO3–] : [H2CO3] ratio, and an increase in pH. Signup and view all the answers

How does fully compensated metabolic alkalosis differ from uncompensated?

Fully compensated metabolic alkalosis has low CO2 content with proportionate decreases in [HCO3–] and [H2CO3], and maintains normal limits for the [HCO3–] : [H2CO3] ratio and pH. Signup and view all the answers

What urinary findings suggest normal kidney function during metabolic alkalosis?

In metabolic alkalosis with normal kidney function, urinary NH3 and titratable acidity both decrease. Signup and view all the answers

List two causes of respiratory alkalosis and their mechanisms.

Two causes of respiratory alkalosis are CNS diseases, like meningitis, which stimulate the respiratory center, and salicylate poisoning, leading to hyperventilation. Signup and view all the answers

How does hyperpyrexia influence respiratory rate and relate to metabolic alkalosis?

Hyperpyrexia increases body temperature, resulting in an elevated respiratory rate which can lead to hyperventilation and contribute to the development of metabolic alkalosis. Signup and view all the answers

What is primarily lost from the stomach in cases of excessive HCl loss, leading to alkalosis?

Chloride ions (Cl–) are primarily lost. Signup and view all the answers

What effect does excessive alkali administration have on the body's bicarbonate levels?

It increases bicarbonate (HCO3–) levels due to conversion of administered bases. Signup and view all the answers

How does hyperventilation contribute to respiratory alkalosis?

Hyperventilation causes excessive loss of CO2, leading to decreased levels of carbonic acid (H2CO3). Signup and view all the answers

In respiratory alkalosis, what compensatory mechanism is primarily utilized by the body?

The renal system compensates by excreting bicarbonate (HCO3–). Signup and view all the answers

What is the typical pH ratio associated with a normal bicarbonate to carbonic acid balance?

The typical pH ratio is 20:1 for [HCO3–]/[H2CO3]. Signup and view all the answers

What ion retention occurs in the blood as a compensatory response during respiratory alkalosis?

Chloride ions (Cl–) are retained in the blood. Signup and view all the answers

What is one consequence of decreased excretion of NH3 in the urine during respiratory alkalosis?

It contributes to the retention of bicarbonate and alkalosis. Signup and view all the answers

What condition is also referred to as a primary H2CO3 deficit?

Respiratory alkalosis is referred to as a primary H2CO3 deficit. Signup and view all the answers

What biochemical changes characterize an uncompensated state in plasma or blood?

Uncompensated states show a disproportionate decrease in [HCO3–] and [H2CO3], leading to decreased pH and total CO2 content. Signup and view all the answers

Describe the characteristics of a fully compensated acid-base state.

In fully compensated states, [HCO3–] and [H2CO3] decrease proportionately, keeping the [HCO3–]:[H2CO3] ratio and pH within normal limits. Signup and view all the answers

What is the urine pH and acidity when there is an abnormal loss of HCO3–?

The urine pH is acidic, with increased excretion of NH4Cl and NaH2PO4. Signup and view all the answers

List two conditions that can lead to respiratory acidosis due to impaired CO2 elimination.

Emphysema and depression of the respiratory center are two conditions that can impair CO2 elimination. Signup and view all the answers

What compensatory mechanism occurs in response to respiratory acidosis?

The renal mechanism becomes more important, while the respiratory mechanism increases respiratory rate and depth to excrete more CO2. Signup and view all the answers

What leads to an abnormal increase in anions other than HCO3- in acid gain?

Diabetic acidosis, starvation, high fever, and lactic acidosis can lead to an abnormal increase in anions. Signup and view all the answers

How does the [HCO3–]/[H2CO3] ratio change in respiratory acidosis?

The [HCO3–]/[H2CO3] ratio decreases in respiratory acidosis due to increased levels of H2CO3. Signup and view all the answers

What factors may contribute to a decrease in carbon dioxide elimination?

Breathing air with high CO2 percentage and pulmonary conditions that impede CO2 elimination contribute to decreased carbon dioxide excretion. Signup and view all the answers

Study Notes

Medical Biochemistry: Acid-Base Imbalance

Acid-base imbalance can manifest as acidosis or alkalosis. Acidosis can be metabolic or respiratory, while alkalosis can also be metabolic or respiratory. Compensated or uncompensated phases exist for all types.

Metabolic Acidosis

Also known as primary alkali deficit, this is the most common acid-base disturbance clinically.
It's caused by a decrease in plasma bicarbonate (HCO₃^-) with little or no change to the H₂CO₃ fraction.
The ratio [HCO₃^-]/[H₂CO₃] = 20/1
A lower ratio means decreased pH, leading to metabolic acidosis.

Primary Compensatory Mechanism (Metabolic Acidosis)

The respiratory center increases breathing rate (Kussmaul respiration) to eliminate excess CO₂ and reduce H₂CO₃.
This restores the [HCO₃^-]/[H₂CO₃] ratio towards 20:1, but eventually, reduced pCO₂ depresses the respiratory centers.
Compensatory mechanisms are only partially effective.
In early stages of the deficit, the body is in a state of compensated acidosis. But worsening conditions and untreated conditions can lead to uncompensated acidosis.

Secondary Compensatory Mechanism (Metabolic Acidosis)

The kidneys increase the formation and excretion of ammonia (NH₃) to secrete excess H⁺ions.
This helps conserve bicarbonate (HCO₃^-).
More H⁺ is excreted and more K⁺ is excreted, compared to H⁺, in the distal tubule.

Biochemical Characteristics (Metabolic Acidosis) - Uncompensated

Significant decrease in [HCO₃^-].
Decreased [H₂CO₃] and pCO₂.
Decrease in total CO₂ content ([HCO₃^-] + [H₂CO₃]).
Decrease in the [HCO₃^-]/[H₂CO₃] ratio.
Decreased pH.

Biochemical Characteristics (Metabolic Acidosis) - Fully Compensated

Low CO₂ content .
Proportional decrease in [HCO₃^- ] and [H₂CO₃] .
[HCO₃^-]/[H₂CO₃] and pH are within normal limits

Urinary Findings (Metabolic Acidosis)

Acidic urine (pH).
Increased excretion of NH₄Cl and NaH₂PO₄.
Increased titratable acidity.

Causes (Metabolic Acidosis)

Excessive gain of acids (e.g., diabetic acidosis, starvation, high fever, violent exercise).
Increased production of acid ions (e.g., lactic acidosis).
Ingestion of acidic salts.
Renal insufficiency.
Impaired acid excretion.
Severe diarrhea (loss of bicarbonate).

Respiratory Acidosis

Characterized by “primary [H₂CO₃] carbonic acid excess.”
Results from an increase in carbon dioxide (CO₂) in the blood (pCO₂↑) due to impaired CO₂ elimination.
Can be caused by breathing air with high CO₂, or impaired lung function (e.g., emphysema) or depressed respiratory centers.

Mechanism (Respiratory Acidosis)

Impaired CO₂ excretion leads to its accumulation, increasing [H₂CO₃].
This lowers [HCO₃^-] / [H₂CO₃] ratio, which leads to decreased pH.
Respiratory compensation becomes secondary, with renal compensation taking on more importance.

Biochemical Characteristics (Respiratory Acidosis) - Uncompensated

Significantly increased [H₂CO₃] (and pCO₂).
Increased [HCO₃^-].
Increased total CO₂ content.
Decreased [HCO₃^-]: [H₂CO₃] ratio.
Decreased pH

Biochemical Characteristics (Respiratory Acidosis) - Fully Compensated

High CO₂ content,
Proportionate increases in [H₂CO₃] & [HCO₃^-],
Ratio [HCO₃^-] : [H₂CO₃] & pH are within normal limits.

Urinary Findings (Respiratory Acidosis)

Increased urinary NH₃.
Increased titratable acidity.