Mechanism of respiration MCQs With Answer

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Mechanism of respiration MCQs With Answer is an essential study resource for B. Pharm students focusing on respiratory physiology, pulmonary ventilation, gas exchange, and cellular respiration. This concise, keyword-rich guide covers mechanics of breathing, alveolar gas laws, oxygen and carbon dioxide transport, hemoglobin-oxygen affinity, surfactant action, ventilation-perfusion relationships, and pharmacological interventions relevant to pulmonary function. Each MCQ is designed to reinforce core concepts such as intrapleural pressure changes, diffusion limitations, chemoreceptor regulation, and acid–base balance, helping you master clinical and theoretical applications. Clear answers are provided to boost retention and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which muscle is the primary active muscle of quiet inspiration?

  • External intercostal
  • Diaphragm
  • Sternocleidomastoid
  • Internal intercostal

Correct Answer: Diaphragm

Q2. During quiet inspiration intrapleural pressure becomes:

  • More positive than atmospheric pressure
  • Less negative (approaches zero)
  • More negative (decreases)
  • Equal to intrapulmonary pressure

Correct Answer: More negative (decreases)

Q3. Boyle’s law, which explains the mechanism of ventilation, states that at constant temperature:

  • Pressure is proportional to volume
  • Pressure is inversely proportional to volume
  • Pressure equals volume squared
  • Pressure is independent of volume

Correct Answer: Pressure is inversely proportional to volume

Q4. Pulmonary surfactant that reduces alveolar surface tension is produced by which cells?

  • Type I pneumocytes
  • Type II pneumocytes
  • Alveolar macrophages
  • Club (Clara) cells

Correct Answer: Type II pneumocytes

Q5. According to Laplace’s law for alveoli, the pressure required to keep an alveolus open is directly proportional to:

  • The cube of alveolar radius
  • Surface tension and inversely proportional to radius
  • AIRFLOW rate
  • Alveolar volume only

Correct Answer: Surface tension and inversely proportional to radius

Q6. Lung compliance is typically decreased in which condition?

  • Emphysema
  • Pulmonary fibrosis
  • Normal aging
  • Asthma during bronchodilation

Correct Answer: Pulmonary fibrosis

Q7. Approximately what percentage of CO2 is transported as bicarbonate (HCO3−) in blood?

  • 7%
  • 23%
  • 70%
  • 100%

Correct Answer: 70%

Q8. The enzyme that catalyzes the conversion of CO2 and H2O to H2CO3 in red blood cells is:

  • Carbonic anhydrase
  • Carboxylase
  • Hemoglobin esterase
  • ATPase

Correct Answer: Carbonic anhydrase

Q9. The Bohr effect describes how which change shifts the oxyhemoglobin dissociation curve to the right?

  • Increased pH (alkalosis)
  • Decreased pH (acidosis)
  • Decreased temperature
  • Decreased PCO2

Correct Answer: Decreased pH (acidosis)

Q10. The Haldane effect refers to the influence of oxygenation of hemoglobin on:

  • Its affinity for oxygen
  • CO2 carrying capacity of blood
  • Plasma bicarbonate formation only
  • Alveolar ventilation

Correct Answer: CO2 carrying capacity of blood

Q11. An increase in body temperature causes the oxyhemoglobin dissociation curve to shift:

  • Left, increasing O2 affinity
  • Right, decreasing O2 affinity
  • No change
  • Initially right then left

Correct Answer: Right, decreasing O2 affinity

Q12. 2,3-Bisphosphoglycerate (2,3-BPG) in red blood cells functions to:

  • Increase hemoglobin affinity for oxygen
  • Decrease hemoglobin affinity for oxygen to facilitate O2 release
  • Convert CO2 to bicarbonate
  • Bind to oxygen directly as an alternative carrier

Correct Answer: Decrease hemoglobin affinity for oxygen to facilitate O2 release

Q13. Hypoxic hypoxia is primarily due to which of the following?

  • Decreased hemoglobin concentration
  • Low arterial PO2 (hypoxemia)
  • Impaired tissue utilization of O2
  • Carbon monoxide poisoning

Correct Answer: Low arterial PO2 (hypoxemia)

Q14. Anemic hypoxia is characterized by which of the following?

  • Normal PaO2 with reduced O2 content due to low hemoglobin
  • Low PaO2 with normal hemoglobin
  • Impaired tissue oxygen utilization despite normal delivery
  • Excessive hemoglobin binding to CO2

Correct Answer: Normal PaO2 with reduced O2 content due to low hemoglobin

Q15. In carbon monoxide (CO) poisoning, arterial PO2 is generally:

  • Markedly decreased
  • Normal because dissolved O2 is unaffected
  • Undetectable
  • Inversely proportional to COHb level

Correct Answer: Normal because dissolved O2 is unaffected

Q16. Fick’s law of diffusion states that gas transfer across a membrane is directly proportional to all EXCEPT:

  • Surface area
  • Diffusion coefficient of the gas
  • Membrane thickness
  • Partial pressure difference across the membrane

Correct Answer: Membrane thickness

Q17. Which gas is primarily diffusion-limited rather than perfusion-limited under normal conditions?

  • Nitrous oxide (N2O)
  • Oxygen (O2) in normal lungs
  • Carbon monoxide (CO)
  • Nitrogen (N2)

Correct Answer: Carbon monoxide (CO)

Q18. The normal ventilation-perfusion (V/Q) ratio for the whole lung is approximately:

  • 0.2
  • 0.8
  • 1.5
  • 2.5

Correct Answer: 0.8

Q19. Physiological dead space increases most characteristically in which condition?

  • Pulmonary embolism
  • Asthma with bronchospasm
  • Pneumonia with consolidation
  • Trace inhalation exposure to irritants

Correct Answer: Pulmonary embolism

Q20. Alveolar ventilation (VA) is calculated by which equation?

  • VA = VT × RR
  • VA = (VT − VD) × RR
  • VA = VD × RR
  • VA = FRC − RV

Correct Answer: VA = (VT − VD) × RR

Q21. The dorsal respiratory group (DRG), primarily responsible for inspiratory rhythm generation, is located in the:

  • Pons
  • Medulla oblongata
  • Cerebellum
  • Hypothalamus

Correct Answer: Medulla oblongata

Q22. Central chemoreceptors respond primarily to changes in:

  • Arterial PO2
  • Arterial pH directly
  • Cerebrospinal fluid H+ derived from CO2
  • Plasma bicarbonate concentration

Correct Answer: Cerebrospinal fluid H+ derived from CO2

Q23. Peripheral chemoreceptors in the carotid bodies are most sensitive to:

  • Low arterial PO2
  • High arterial bicarbonate
  • Changes in blood glucose
  • Plasma protein levels

Correct Answer: Low arterial PO2

Q24. During moderate exercise, minute ventilation increases primarily due to:

  • Increase in anatomical dead space only
  • Increase in tidal volume and some increase in respiratory rate
  • Decrease in metabolic CO2 production
  • Profound decrease in arterial PO2

Correct Answer: Increase in tidal volume and some increase in respiratory rate

Q25. Hyperventilation causes which primary acid–base disturbance?

  • Metabolic acidosis
  • Respiratory alkalosis
  • Metabolic alkalosis
  • Respiratory acidosis

Correct Answer: Respiratory alkalosis

Q26. In metabolic acidosis, respiratory compensation results in which change?

  • Hypoventilation to retain CO2
  • Hyperventilation to reduce PaCO2
  • No change in ventilation
  • Irregular apneic episodes

Correct Answer: Hyperventilation to reduce PaCO2

Q27. Which lung volume cannot be measured by simple spirometry?

  • Tidal volume (VT)
  • Vital capacity (VC)
  • Residual volume (RV)
  • Inspiratory capacity (IC)

Correct Answer: Residual volume (RV)

Q28. A reduced FEV1/FVC ratio is characteristic of which pattern?

  • Restrictive lung disease
  • Obstructive lung disease
  • Normal pulmonary function
  • Pulmonary vascular disease

Correct Answer: Obstructive lung disease

Q29. In restrictive lung disease which spirometry pattern is typically observed?

  • Decreased TLC with normal or increased FEV1/FVC ratio
  • Increased TLC with decreased FEV1/FVC ratio
  • Normal TLC and decreased FEV1/FVC ratio
  • Only increased residual volume

Correct Answer: Decreased TLC with normal or increased FEV1/FVC ratio

Q30. Neonatal respiratory distress syndrome is mainly due to deficiency of:

  • Surfactant (low lecithin)
  • Type I pneumocytes
  • Fetal hemoglobin
  • Bronchial smooth muscle tone

Correct Answer: Surfactant (low lecithin)

Q31. Which drug is a short-acting beta-2 adrenergic agonist used for acute bronchodilation?

  • Salbutamol (albuterol)
  • Budesonide
  • Ipratropium
  • Theophylline

Correct Answer: Salbutamol (albuterol)

Q32. Which bronchodilator acts as an inhaled anticholinergic by blocking muscarinic receptors?

  • Salmeterol
  • Ipratropium
  • Zafirlukast
  • Montelukast

Correct Answer: Ipratropium

Q33. Theophylline, a methylxanthine bronchodilator, primarily exerts effects by:

  • Beta-2 receptor agonism
  • Inhibition of phosphodiesterase increasing cAMP
  • Leukotriene receptor antagonism
  • Blocking histamine H1 receptors

Correct Answer: Inhibition of phosphodiesterase increasing cAMP

Q34. Inhaled corticosteroids improve asthma control mainly by:

  • Immediate bronchodilation via smooth muscle relaxation
  • Reducing airway inflammation and cytokine production
  • Blocking leukotriene synthesis directly
  • Antagonizing muscarinic receptors

Correct Answer: Reducing airway inflammation and cytokine production

Q35. Montelukast is classified pharmacologically as a:

  • Beta-2 agonist
  • Leukotriene receptor antagonist
  • Short-acting muscarinic antagonist
  • Systemic corticosteroid

Correct Answer: Leukotriene receptor antagonist

Q36. Pulmonary capillary wedge pressure is used clinically as an estimate of:

  • Right atrial pressure
  • Pulmonary vascular resistance
  • Left atrial pressure (left ventricular preload)
  • Pulmonary artery systolic pressure

Correct Answer: Left atrial pressure (left ventricular preload)

Q37. Central cyanosis becomes clinically apparent when deoxygenated hemoglobin exceeds approximately:

  • 1 g/dL
  • 3 g/dL
  • 5 g/dL
  • 10 g/dL

Correct Answer: 5 g/dL

Q38. The alveolar gas equation shows alveolar PO2 is inversely related to:

  • Inspired oxygen fraction (FIO2)
  • Alveolar CO2 partial pressure (PaCO2) divided by respiratory quotient (R)
  • Barometric pressure only
  • Hemoglobin concentration

Correct Answer: Alveolar CO2 partial pressure (PaCO2) divided by respiratory quotient (R)

Q39. Total arterial oxygen content (CaO2) depends primarily on which variable?

  • Arterial PO2 alone
  • Hemoglobin concentration and SaO2
  • Plasma bicarbonate concentration
  • Partial pressure of CO2

Correct Answer: Hemoglobin concentration and SaO2

Q40. A right-to-left shunt causes hypoxemia that is:

  • Corrected fully by 100% oxygen
  • Not corrected well by supplemental oxygen
  • Due to increased physiological dead space
  • Always caused by pulmonary embolism

Correct Answer: Not corrected well by supplemental oxygen

Q41. Thickening of the alveolar-capillary membrane most directly impairs which process?

  • Perfusion of pulmonary capillaries
  • Diffusion of oxygen across the membrane
  • Hemoglobin synthesis
  • Bronchial smooth muscle contraction

Correct Answer: Diffusion of oxygen across the membrane

Q42. Chronic pulmonary hypertension can lead to enlargement and failure of which cardiac chamber?

  • Left ventricle
  • Right ventricle
  • Left atrium
  • Right atrium only

Correct Answer: Right ventricle

Q43. The afferent limb of the cough reflex is primarily mediated by which nerve supplying airway receptors?

  • Phrenic nerve
  • Vagus nerve
  • Glossopharyngeal nerve
  • Facial nerve

Correct Answer: Vagus nerve

Q44. The ventral respiratory group (VRG) primarily contributes to which aspect of breathing?

  • Quiet inspiration only
  • Forced inspiration and expiration (active breathing)
  • Regulation of heart rate
  • Long-term oxygen sensing

Correct Answer: Forced inspiration and expiration (active breathing)

Q45. Opioid drugs produce respiratory depression mainly by:

  • Stimulating peripheral chemoreceptors
  • Depressing brainstem respiratory centers and reducing CO2 sensitivity
  • Blocking neuromuscular transmission in respiratory muscles
  • Increasing lung compliance dramatically

Correct Answer: Depressing brainstem respiratory centers and reducing CO2 sensitivity

Q46. The most common cause of hypoxemia in clinical practice is:

  • Low inspired oxygen at high altitude
  • Ventilation-perfusion (V/Q) mismatch
  • Pure diffusion impairment alone
  • Right-to-left intracardiac shunt in young adults

Correct Answer: Ventilation-perfusion (V/Q) mismatch

Q47. Chronic hypoxia increases red blood cell 2,3-BPG which results in:

  • Left shift of oxyhemoglobin curve increasing O2 affinity
  • Right shift of oxyhemoglobin curve promoting O2 unloading
  • No change in oxygen unloading
  • Reduced tissue oxygen delivery

Correct Answer: Right shift of oxyhemoglobin curve promoting O2 unloading

Q48. The immediate recommended treatment for severe carbon monoxide poisoning is:

  • 100% oxygen and consideration of hyperbaric oxygen therapy
  • Administration of methylene blue
  • Exchange transfusion only
  • High-flow nitrogen inhalation

Correct Answer: 100% oxygen and consideration of hyperbaric oxygen therapy

Q49. Diffusing capacity of the lung for carbon monoxide (DLCO) is typically decreased in:

  • Emphysema due to loss of alveolar surface area
  • Asthma during acute bronchodilation
  • Obesity with normal lungs
  • Acute upper airway obstruction

Correct Answer: Emphysema due to loss of alveolar surface area

Q50. A normal alveolar-arterial (A–a) oxygen gradient in a young healthy adult breathing room air is approximately:

  • 0–2 mmHg
  • 5–15 mmHg
  • 30–40 mmHg
  • Over 50 mmHg

Correct Answer: 5–15 mmHg

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