Clinical Chemistry: Acid-Base Balance

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Questions and Answers

What is the normal range of blood pH?

7.1-7.7

7.2-7.6

7.35-7.45 (correct)

6.8-7.8

What would be the effect of a blood pH below 6.8 or above 7.8?

Increased oxygen delivery to tissues

Electrolyte imbalance only

No effect on oxygen delivery

Reduced oxygen delivery to tissues (correct)

What is the term used for a blood pH greater than 7.45?

Acidosis

Homeostasis

Alkalosis (correct)

Acid-base balance

What is the primary buffer system in blood?

Bicarbonate buffer Signup and view all the answers

What is the role of the respiratory mechanism in acid-base balance?

Removal of excess hydrogen ions Signup and view all the answers

What is the equation that relates pH to the concentrations of HCO3- and H2CO3?

Henderson-Hasselbalch equation Signup and view all the answers

What happens when a strong acid like HCl is added to the bicarbonate buffer?

HCO3- and H+ combine to form H2CO3 Signup and view all the answers

Why is it essential to maintain blood pH within a narrow range?

To maintain normal cell metabolism Signup and view all the answers

What is the formula for pH in terms of HCO3- and H2CO3 concentrations?

pH = 6.1 + log ([HCO3-] / [H2CO3]) Signup and view all the answers

What is the primary function of the lungs in acid-base balance?

To excrete excess CO2 from the blood Signup and view all the answers

What is the enzyme found in renal tubule cells that facilitates the formation of carbonic acid?

Carbonic anhydrase Signup and view all the answers

What is the consequence of a rise in CO2 concentration in the blood?

Increased ventilation Signup and view all the answers

What is the primary site of hydrogen ion elimination in the body?

Kidneys Signup and view all the answers

What is the name of the blood test used to identify and monitor acid-base disturbances?

Arterial Blood Gases (ABG) Signup and view all the answers

What is the result of a disturbance in acid-base balance?

Disease or damage to organs Signup and view all the answers

What is the direction of the reaction between CO2, H2O, and carbonic acid?

Reversible Signup and view all the answers

What is the primary cause of respiratory acidosis?

Inadequate alveolar ventilation Signup and view all the answers

Which of the following conditions is associated with respiratory alkalosis?

Severe anemia Signup and view all the answers

What happens to bicarbonate concentration in metabolic acidosis?

It decreases Signup and view all the answers

What is the renal compensation for respiratory acidosis?

Increased reabsorption of bicarbonate Signup and view all the answers

What is the characteristic of metabolic alkalosis?

Increased bicarbonate concentration Signup and view all the answers

What is the compensation for metabolic acidosis?

Decreased pCO2 Signup and view all the answers

What is the result of excessive alveolar ventilation in respiratory alkalosis?

Increased elimination of CO2 from blood Signup and view all the answers

What is the characteristic of respiratory acidosis?

Increased pCO2 Signup and view all the answers

Study Notes

Acid-Base Balance

Normal blood pH range is 7.35-7.45, and any variation outside this range can have deleterious effects, including reduced oxygen delivery to tissues, electrolyte disturbances, and changes in heart muscle contractility.
Survival is rare if blood pH falls below 6.8 or rises above 7.8.

Maintenance of Blood pH

The body has three lines of defense to regulate acid-base balance and maintain blood pH:
- Blood buffers
- Respiratory mechanism
- Renal mechanism

Blood Buffer

The principal buffer system in blood is the weak acid, carbonic acid (H2CO3), and its conjugate base, bicarbonate (HCO3–).
The Henderson-Hasselbalch equation shows that pH is governed by the ratio of base [HCO3–] concentration to acid [H2CO3] concentration: pH = 6.1 + log ([HCO3–] / [H2CO3])

Role of the Lung in Acid-Base Balance

The lungs ensure removal of carbonic acid (as CO2) by regulating the rate of CO2 excretion through ventilation.
Respiratory chemoreceptors in the brain respond to changes in CO2 concentration, causing increased ventilation if CO2 concentration rises and decreased ventilation if CO2 falls.

Role of the Kidneys in Acid-Base Balance

The kidneys eliminate hydrogen ions and regenerate bicarbonate through the enzyme carbonic anhydrase.
Carbonic acid dissociates to bicarbonate and hydrogen ions, and the bicarbonate is reabsorbed into blood while the hydrogen ions are eliminated in urine.

Disturbances of Acid-Base Balance

Disturbances occur due to disease or damage to organs necessary for acid-base homeostasis.
Arterial blood gases (ABG) are used to identify and monitor acid-base disturbances, measuring:
- Arterial blood pH
- Partial pressure of carbon dioxide (pCO2)
- Concentration of bicarbonate (HCO3–)

Arterial pH

Decreased pH (acidemia) is associated with acidosis, while increased pH (alkalemia) is associated with alkalosis.

Types of Acidosis and Alkalosis

Respiratory acidosis: increased pCO2 due to inadequate alveolar ventilation, often associated with respiratory diseases or drugs.
Respiratory alkalosis: decreased pCO2 due to excessive alveolar ventilation, often associated with severe anemia, pulmonary embolism, and adult respiratory syndrome.
Metabolic acidosis: reduced bicarbonate due to increased acid load or losses of bicarbonate from the body.
Metabolic alkalosis: increased bicarbonate, often associated with compensation mechanisms involving depression of respiration and retention of carbon dioxide.

Compensation Mechanisms

Renal compensation for respiratory acidosis: increased reabsorption of bicarbonate.
Renal compensation for respiratory alkalosis: reduced bicarbonate reabsorption.
Compensation for metabolic acidosis: lower pCO2.
Compensation for metabolic alkalosis: elevation of pCO2.

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Description

This quiz covers the basics of acid-base balance in clinical chemistry, including the importance of maintaining blood pH within a narrow range and the effects of variations outside this range.