BSCI202: Acid Base Imbalance

Dr. Justicia Opoku

To maintain homeostasis, the human body maintains an acid-base balance of the blood pH between ___ to ___.

7.35; 7.45

Why does the blood pH for acid-base balance have such a narrow range?

Most enzymes that catalyze physiological reactions prefer this pH range

A blood pH below 7.35 is termed ________.

Acidosis

A blood pH above 7.45 is termed ________.

Alkalosis

What are the two main categories of acid-base imbalances?

Respiratory disturbances and Metabolic disturbances

Respiratory disturbances is also known as what?

Respiratory acid-base imbalances

What are the sub-conditions of respiratory disturbances?

Respiratory acidosis and Respiratory alkalosis

Respiratory acidosis is due to what? How does this affect blood CO2 levels?

Hypoventilation; increases blood CO2 levels

What is the rate of alveolar ventilation in respiratory acidosis?

Rate of alveolar ventilation falls behind CO2 production

Respiratory alkalosis is due to what? How does this affect blood CO2?

Hyperventilation; decreases blood CO2 levels

What is the rate of CO₂ elimination in respiratory alkalosis?

CO2 is eliminated faster than it is produced

Metabolic disturbances is also known as what?

Metabolic acid-base imbalances

What are the sub-conditions of metabolic disturbances?

Metabolic acidosis and Metabolic alkalosis

Metabolic acidosis is due to what? (process)

Addition of metabolic acids to blood or loss of HCO3- from the blood

What are some triggers that cause metabolic acidosis?

Strenuous exercise, starvation, alcoholism, diabetes, acidic drugs (aspirin)

Metabolic alkalosis is due to what? (process)

Loss of metabolic acids from blood or addition of HCO3-

What are some triggers that cause metabolic alkalosis?

This condition is rare; some triggers are overuse of bicarbonates (antacids), loss of acid (chronic vomiting)

What are the disorders of acid-base balances?

Respiratory acidosis, Respiratory alkalosis, Metabolic acidosis, Metabolic alkalosis

What chemical compound is a source of acid?

Carbon dioxide

What is the chemical equation for CO2 in the blood?

CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+

This is the equation for CO2 in the blood - Why does it matter for acid-base balance?

Free H+ dictates blood pH; CO2 acts as an acid source

In respiratory acid-base imbalances, how do HCO₃⁻ and H⁺ change relative to each other?

They change in the SAME direction (both decrease together or both increase together) because both come from H2CO3

What happens to blood pH and PCO2 in respiratory acidosis?

Increased PCO2 causes increased blood H+ and decreased blood pH below 7.35

What is the kidney's compensatory mechanism for respiratory acidosis?

A-type intercalated cells increase H+ excretion and increase HCO3- reabsorption

What happens to blood pH and PCO2 in respiratory alkalosis?

Decreased PCO2 causes decreased blood H+ and increased blood pH above 7.45

What is the kidney's compensatory mechanism for respiratory alkalosis?

B-type intercalated cells increase HCO3- excretion and increase H+ reabsorption

What causes metabolic acidosis via increased metabolic acids?

High protein diet (amino acids), high fat diet (fatty acids), heavy exercise (lactic acid), and severe diarrhea (loss of bicarbonate)

How does renal dysfunction cause metabolic acidosis?

Fails to secrete H+

What is the immediate compensatory mechanism for metabolic acidosis?

Hyperventilation increases CO2 expired, decreasing blood CO2 and H+ to raise pH

What is the renal compensatory mechanism for metabolic acidosis?

Type A intercalated cells increase H+ excretion and HCO3- reabsorption to increase blood pH

How does alcohol consumption cause metabolic acidosis?

Alcohol is metabolized to acetaldehyde then to acetic acid, contributing metabolic acids to blood

How does strenuous exercise cause metabolic acidosis?

It produces lactic acid via anaerobic catabolism of glucose

How does starvation or untreated diabetes cause metabolic acidosis?

Low insulin increases lipolysis, releasing free fatty acids that are converted to ketone bodies (acetoacetic acid, beta-hydroxybutyric acid, acetone)

How does aspirin overdose cause metabolic acidosis?

Aspirin is metabolized into acetylsalicylic acid, and overdose presents as metabolic acidosis

What causes metabolic alkalosis via loss of H+?

Excessive vomiting (hyperemesis) loses hydrogen ions from the stomach, so H+ shifts from blood into stomach, dropping blood H+ and increasing pH

What causes metabolic alkalosis via alkaline products?

Consumption of baking soda or antacids neutralizes stomach acid, causing H+ to shift from blood into stomach, dropping blood H⁺ and increasing pH

What is the immediate compensatory mechanism for metabolic alkalosis?

Hypoventilation increases blood CO2, which increases blood H+ to decrease pH toward normal

When metabolic alkalosis is not corrected by hypoventilation, renal compensatory mechanism is activated. What is the renal compensatory mechanism for metabolic alkalosis?

Type B intercalated cells increase HCO3- excretion and H+ reabsorption to increase blood H+ and decrease pH

What are possible causes of respiratory acidosis?

Impaired lung function (bronchitis, emphysema, pneumonia, pulmonary edema), impaired ventilatory movement (paralyzed muscles, chest injury, obesity), or brain stem depression (narcotic/barbiturate overdose, injury)

What are possible causes of respiratory alkalosis?

Strong emotions (pain, anxiety, panic), hypoxemia (asthma, pneumonia, high altitude), or brain tumor/injury

What are possible causes of metabolic acidosis?

Severe diarrhea, renal disease, untreated diabetes mellitus, starvation, and excess alcohol ingestion.

What are possible causes of metabolic alkalosis?

Vomiting or gastric suctioning, selected diuretics (K⁺ depletion), excessive sodium bicarbonate (antacids), and excess aldosterone (adrenal tumors)

If you encounter a patient who is hypoventilating, how would you know if the patient is developing respiratory acidosis or if the patient is using hypoventilation as a compensatory mechanism for metabolic alkalosis?

Hypoventilation with a pulmonary disorder causes respiratory acidosis, but hypoventilation after vomiting or antacid ingestion compensates for metabolic alkalosis

If you encounter a patient who is hyperventilating, how would you know if the patient is developing respiratory alkalosis or if the patient is using hyperventilation as a compensatory mechanism for metabolic acidosis?

Hyperventilation from panic attack or high altitude causes respiratory alkalosis, but hyperventilation from diarrhea, starvation, diabetes, alcohol, aspirin overdose, or kidney disease compensates for metabolic acidosis

Fill in the red blanks: Metabolic acidosis

Decrease; Increase; Decrease [HCO3-]; decrease pCO2

Fill in the red blanks: Metabolic alkalosis

Increase; Decrease; Increase [HCO3-]; increase pCO2

Fill in the red blanks: Respiratory acidosis*

Decrease; Increase; Increase [pCO2]; Increase [HCO3-]

Fill in the red blanks: Respiratory alkalosis*

Increase; Decrease; Decrease [pCO2]; Decrease [HCO3-]