Regulation of breathing MCQs With Answer

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Regulation of breathing MCQs With Answer is an essential resource for B. Pharm students studying respiratory physiology and pharmacology. This concise, Student-friendly post covers neural and chemical control of ventilation, central and peripheral chemoreceptors, lung reflexes, ventilation–perfusion balance, and drug effects on respiratory drive. Designed for exam prep and practical understanding, these MCQs emphasize mechanisms — medullary respiratory centers, pre-Bötzinger complex, Hering–Breuer reflex, carotid and aortic bodies, CO2/O2/pH sensing, and pharmacologic modulators like opioids, doxapram, and theophylline. Strengthen your clinical reasoning and drug-related knowledge with focused practice questions. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which structure is considered the primary respiratory rhythm generator in the medulla?

  • Apneustic center
  • Pneumotaxic center
  • Pre-Bötzinger complex
  • Dorsal respiratory group

Correct Answer: Pre-Bötzinger complex

Q2. Central chemoreceptors located on the ventral surface of the medulla primarily respond to changes in which of the following?

  • Arterial O2 tension (PaO2)
  • Plasma bicarbonate concentration
  • CSF hydrogen ion concentration (pH) secondary to PaCO2
  • Carotid sinus baroreceptor activity

Correct Answer: CSF hydrogen ion concentration (pH) secondary to PaCO2

Q3. Peripheral chemoreceptors in the carotid bodies are most sensitive to which change?

  • Mild hypercapnia when PaO2 is normal
  • Drop in PaO2 below approximately 60 mmHg
  • Increase in plasma bicarbonate
  • Increase in arterial pH

Correct Answer: Drop in PaO2 below approximately 60 mmHg

Q4. Which reflex prevents overinflation of the lungs during deep inspiration?

  • Cough reflex
  • Baroreceptor reflex
  • Gag reflex

Correct Answer: Hering–Breuer reflex

Q5. Which group of neurons is primarily active during inspiration and located in the nucleus tractus solitarius?

  • Ventral respiratory group (VRG)
  • Dorsal respiratory group (DRG)
  • Pneumotaxic center
  • Apneustic center

Correct Answer: Dorsal respiratory group (DRG)

Q6. The alveolar gas equation is used to estimate PAO2. Which simplified form is correct?

  • PAO2 = PIO2 + (PaCO2 × R)
  • PAO2 = PIO2 − (PaCO2 / R)
  • PAO2 = PaO2 − PaCO2
  • PAO2 = PaO2 × SaO2

Correct Answer: PAO2 = PIO2 − (PaCO2 / R)

Q7. Which condition most directly reduces the chemosensitivity of central chemoreceptors to CO2?

  • Acute metabolic acidosis
  • Chronic hypercapnia with renal compensation
  • Acute hypoxia
  • Increased 2,3-BPG

Correct Answer: Chronic hypercapnia with renal compensation

Q8. Which receptor type in the lungs responds to pulmonary edema and causes rapid shallow breathing and dyspnea?

  • Stretch receptors
  • Irritant receptors
  • J (juxtacapillary) receptors
  • Baroreceptors

Correct Answer: J (juxtacapillary) receptors

Q9. Which of the following shifts the oxygen–hemoglobin dissociation curve to the right?

  • Decrease in temperature
  • Increase in pH (alkalosis)
  • Increase in 2,3-BPG
  • Carbon monoxide exposure

Correct Answer: Increase in 2,3-BPG

Q10. How does carbon monoxide poisoning primarily impair oxygen delivery?

  • Decreases PaO2 by displacing O2 in plasma
  • Reduces hemoglobin concentration by hemolysis
  • Forms carboxyhemoglobin, decreasing O2 carrying capacity and shifting curve left
  • Increases ventilation causing respiratory alkalosis

Correct Answer: Forms carboxyhemoglobin, decreasing O2 carrying capacity and shifting curve left

Q11. Ventilation–perfusion (V/Q) mismatch is best described by which statement?

  • All alveoli are equally perfused and ventilated in V/Q mismatch
  • V/Q mismatch only occurs in pulmonary embolism
  • Gas exchange is impaired when ventilation and perfusion are not properly matched across lung units
  • V/Q mismatch can be corrected by increasing hemoglobin concentration

Correct Answer: Gas exchange is impaired when ventilation and perfusion are not properly matched across lung units

Q12. Which of the following is a perfusion-limited gas under normal physiology?

  • Oxygen during exercise at high cardiac output
  • Carbon monoxide (CO)
  • Carbon dioxide (CO2)
  • Oxygen under all conditions

Correct Answer: Carbon dioxide (CO2)

Q13. The primary drive to breathe in a healthy adult at sea level is governed by which parameter?

  • Arterial PO2
  • Arterial PCO2
  • Arterial bicarbonate
  • Peripheral chemoreceptor stimulation by lactate

Correct Answer: Arterial PCO2

Q14. Which drug is commonly known to cause dose-dependent respiratory depression by acting on μ-opioid receptors in the brainstem?

  • Atropine
  • Fentanyl
  • Doxapram
  • Theophylline

Correct Answer: Fentanyl

Q15. Doxapram stimulates respiration primarily by acting on which site?

  • Central chemoreceptors in medulla
  • Peripheral chemoreceptors in carotid bodies
  • Alveolar stretch receptors
  • Cerebral cortex respiratory centers

Correct Answer: Peripheral chemoreceptors in carotid bodies

Q16. Which equation gives the total arterial O2 content (CaO2)?

  • CaO2 = PaO2 × 0.003 + (Hb × 1.34 × SaO2)
  • CaO2 = PaO2 + PaCO2
  • CaO2 = Hb × PaO2
  • CaO2 = SaO2 × 100

Correct Answer: CaO2 = PaO2 × 0.003 + (Hb × 1.34 × SaO2)

Q17. Which of the following best describes a physiologic shunt?

  • Ventilated alveoli without perfusion
  • Perfused alveoli without ventilation
  • Areas with equal ventilation and perfusion
  • Increased anatomical dead space

Correct Answer: Perfused alveoli without ventilation

Q18. Which pulmonary reflex is mediated by rapidly adapting irritant receptors and triggers cough and bronchoconstriction?

  • Hering–Breuer reflex
  • Irritant receptor reflex
  • Baroreceptor reflex
  • Chemoreceptor reflex

Correct Answer: Irritant receptor reflex

Q19. During exercise, ventilation increases in proportion to metabolic CO2 production. Which mechanism is most responsible for the immediate increase at exercise onset?

  • Slow renal compensation
  • Central command and afferent signals from moving limbs
  • Adaptive increase of 2,3-BPG
  • Increased hematocrit

Correct Answer: Central command and afferent signals from moving limbs

Q20. Which factor does NOT shift the O2–Hb dissociation curve to the right?

  • Increased CO2
  • Increased temperature
  • Decreased 2,3-BPG
  • Decreased pH (acidosis)

Correct Answer: Decreased 2,3-BPG

Q21. Which statement about hypoxic pulmonary vasoconstriction (HPV) is correct?

  • HPV diverts blood away from poorly ventilated lung regions to better ventilated areas
  • HPV increases perfusion to hypoxic alveoli to improve oxygenation
  • HPV is primarily mediated by peripheral chemoreceptors
  • HPV results in systemic vasodilation

Correct Answer: HPV diverts blood away from poorly ventilated lung regions to better ventilated areas

Q22. Chronic hypoventilation with CO2 retention leads to which renal compensation?

  • Decreased bicarbonate reabsorption
  • Increased bicarbonate retention to normalize pH
  • Increased chloride retention only
  • Immediate renal compensation within minutes

Correct Answer: Increased bicarbonate retention to normalize pH

Q23. Which anesthetic class most commonly depresses the ventilatory response to CO2?

  • Inhalational anesthetics (e.g., isoflurane)
  • Antibiotics
  • Proton pump inhibitors
  • Thyroid hormones

Correct Answer: Inhalational anesthetics (e.g., isoflurane)

Q24. Which statement best describes alveolar dead space?

  • Ventilated alveoli that are not perfused
  • Perfused alveoli that are not ventilated
  • Volume of conducting airways only
  • Portion of tidal volume that participates in gas exchange

Correct Answer: Ventilated alveoli that are not perfused

Q25. Which parameter is directly measured to calculate minute ventilation?

  • Tidal volume × respiratory rate
  • Alveolar ventilation × respiratory rate
  • PaO2 × SaO2
  • Hb × SaO2

Correct Answer: Tidal volume × respiratory rate

Q26. What is the main effect of opioids on the respiratory pattern?

  • Increased tidal volume with increased rate
  • Decreased ventilatory response to CO2 and slowed respiratory rate
  • Enhanced peripheral chemoreceptor sensitivity
  • Bronchodilation via β2 stimulation

Correct Answer: Decreased ventilatory response to CO2 and slowed respiratory rate

Q27. Which molecule produced in red blood cells facilitates O2 unloading in tissues by binding to hemoglobin?

  • Carbonic anhydrase
  • 2,3-Bisphosphoglycerate (2,3-BPG)
  • Carboxyhemoglobin
  • Myoglobin

Correct Answer: 2,3-Bisphosphoglycerate (2,3-BPG)

Q28. The ventilatory response to hypoxia is mainly mediated by which of these?

  • Central chemoreceptors sensing CSF pH
  • Peripheral chemoreceptors (carotid bodies)
  • Pulmonary stretch receptors
  • Herring bodies in hypothalamus

Correct Answer: Peripheral chemoreceptors (carotid bodies)

Q29. Which condition would blunt the ventilatory response to hypoxia in chronic COPD patients?

  • Enhanced peripheral chemoreceptor sensitivity
  • Chronic hypercapnia with central chemoreceptor desensitization
  • Acute respiratory alkalosis
  • Increased cardiac output

Correct Answer: Chronic hypercapnia with central chemoreceptor desensitization

Q30. Which drug acts as an adenosine receptor antagonist and can stimulate respiratory drive at toxic doses?

  • Theophylline
  • Succinycholine
  • Metoprolol
  • Ranitidine

Correct Answer: Theophylline

Q31. Which of the following best explains why PaO2 monitoring alone can be misleading for oxygen delivery assessment?

  • PaO2 directly determines hemoglobin concentration
  • Oxygen content depends on hemoglobin concentration and saturation, not just PaO2
  • PaO2 is identical to CaO2 in all circumstances
  • PaO2 measures dissolved CO2, not O2

Correct Answer: Oxygen content depends on hemoglobin concentration and saturation, not just PaO2

Q32. Which of the following reduces the effectiveness of alveolar ventilation for CO2 elimination?

  • Increased alveolar surface area
  • Increased physiologic dead space
  • Decreased anatomic dead space
  • Higher tidal volumes reaching alveoli

Correct Answer: Increased physiologic dead space

Q33. Which center in the pons modulates the transition between inspiration and expiration, limiting inspiratory time?

  • Apneustic center
  • Pneumotaxic center
  • Pre-Bötzinger complex
  • Dorsal respiratory group

Correct Answer: Pneumotaxic center

Q34. Which gas exchange abnormality is least likely to correct with 100% oxygen administration?

  • Hypoventilation-induced hypoxemia
  • Low inspired oxygen (high altitude)
  • Right-to-left shunt (significant physiologic shunt)
  • Diffusion limitation due to emphysema

Correct Answer: Right-to-left shunt (significant physiologic shunt)

Q35. What effect does increased metabolic acidosis have on ventilation?

  • It decreases ventilatory drive to conserve CO2
  • It increases ventilation to blow off CO2 and compensate
  • It has no effect on ventilation
  • It causes immediate renal excretion of bicarbonate without ventilatory change

Correct Answer: It increases ventilation to blow off CO2 and compensate

Q36. Which of the following best describes the Haldane effect?

  • Oxygenation of hemoglobin decreases its affinity for CO2, promoting CO2 release in the lungs
  • CO2 increases affinity of hemoglobin for O2 in tissues
  • Increased temperature enhances CO2 binding to hemoglobin
  • 2,3-BPG binds CO2 and increases its transport

Correct Answer: Oxygenation of hemoglobin decreases its affinity for CO2, promoting CO2 release in the lungs

Q37. Which of these is a common pharmacologic respiratory stimulant used in acute respiratory depression due to drugs?

  • Naloxone for opioid overdose
  • Propranolol for beta-blocker overdose
  • Furosemide for pulmonary edema
  • Insulin for hyperkalemia

Correct Answer: Naloxone for opioid overdose

Q38. In the context of ventilation, what does “dead space” refer to?

  • Portion of stroke volume not ejected by heart
  • Volume of inspired air that does not take part in gas exchange
  • Alveoli with excessive perfusion
  • Volume of blood bypassing the lungs

Correct Answer: Volume of inspired air that does not take part in gas exchange

Q39. Which of the following best characterizes central sleep apnea?

  • Obstruction of upper airway during sleep with continued respiratory effort
  • Reduced central respiratory drive leading to intermittent cessation of effort
  • Primary hyperventilation during sleep
  • Excessive nasal secretions causing apnea

Correct Answer: Reduced central respiratory drive leading to intermittent cessation of effort

Q40. Which ionic change in cerebrospinal fluid is the signal that central chemoreceptors detect when arterial CO2 rises?

  • Increased bicarbonate originating from CSF buffering
  • Increased hydrogen ion concentration due to CO2 hydration
  • Increased sodium concentration
  • Decreased potassium concentration

Correct Answer: Increased hydrogen ion concentration due to CO2 hydration

Q41. Which physiologic adaptation occurs during acclimatization to high altitude to improve oxygen delivery?

  • Decreased 2,3-BPG in red blood cells
  • Increased hemoglobin concentration and 2,3-BPG levels
  • Suppressed ventilation due to reduced chemoreceptor sensitivity
  • Decreased cardiac output permanently

Correct Answer: Increased hemoglobin concentration and 2,3-BPG levels

Q42. Which statement best describes diffusion-limited gas exchange?

  • Gas equilibration is limited by blood flow through pulmonary capillaries
  • Gas transfer is limited by the diffusion capacity of the alveolar–capillary membrane
  • Occurs only for CO2 under all circumstances
  • Is improved by reducing alveolar surface area

Correct Answer: Gas transfer is limited by the diffusion capacity of the alveolar–capillary membrane

Q43. Which measurement increases when physiologic dead space increases?

  • Alveolar ventilation for a given minute ventilation
  • PaO2 for a given minute ventilation
  • PaCO2 if minute ventilation is unchanged
  • Hemoglobin concentration

Correct Answer: PaCO2 if minute ventilation is unchanged

Q44. Which drug class can antagonize opioid-induced respiratory depression when given systemically?

  • Beta-adrenergic agonists
  • Opioid antagonists (e.g., naloxone)
  • Calcium channel blockers
  • H2 receptor antagonists

Correct Answer: Opioid antagonists (e.g., naloxone)

Q45. Which receptor population provides afferent input to the respiratory centers about blood pressure and can indirectly influence ventilation?

  • Pulmonary stretch receptors
  • Carotid sinus baroreceptors
  • Irritant receptors
  • Juxtacapillary receptors

Correct Answer: Carotid sinus baroreceptors

Q46. Which of the following is true about the ventilatory response curve to CO2 after administration of a respiratory depressant drug?

  • The slope increases, enhancing CO2 sensitivity
  • The curve shifts left with increased baseline ventilation
  • The slope decreases, reducing ventilatory sensitivity to CO2
  • The response becomes independent of PaCO2

Correct Answer: The slope decreases, reducing ventilatory sensitivity to CO2

Q47. Which of the following best explains why chronic COPD patients may rely more on hypoxic drive for ventilation?

  • They have increased central chemoreceptor sensitivity to CO2
  • Chronic hypercapnia desensitizes central chemoreceptors, making hypoxia a more important stimulus
  • They have elevated arterial O2 tensions
  • Peripheral chemoreceptors are suppressed permanently

Correct Answer: Chronic hypercapnia desensitizes central chemoreceptors, making hypoxia a more important stimulus

Q48. Which clinical intervention improves V/Q matching by recruiting poorly ventilated alveoli?

  • Increasing FiO2 only without PEEP
  • Positive end-expiratory pressure (PEEP) to open collapsed alveoli
  • Lowering hemoglobin concentration
  • Administering systemic vasodilators to pulmonary circulation

Correct Answer: Positive end-expiratory pressure (PEEP) to open collapsed alveoli

Q49. Which laboratory change is most characteristic of acute respiratory alkalosis from hyperventilation?

  • Increased PaCO2 and decreased pH
  • Decreased PaCO2 and increased pH
  • Increased HCO3- immediately due to renal compensation
  • Increased PaCO2 with metabolic acidosis

Correct Answer: Decreased PaCO2 and increased pH

Q50. Which statement about carotid body glomus (type I) cells is correct?

  • They respond primarily to increases in arterial pH
  • They depolarize when PaO2 falls, releasing neurotransmitters to increase ventilation
  • They are part of the central chemoreceptor network in the medulla
  • They sense alveolar stretch rather than blood gas changes

Correct Answer: They depolarize when PaO2 falls, releasing neurotransmitters to increase ventilation

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