Free Respiratory Physiology MCQs with Answers

• A. 0.5 L
• B. 2.0 L
• C. 1.1 L
• D. 1.8 L

Explanation: Air remaining after maximal forced expiration is the residual volume, which is approximately 1.1 L in an average woman.

• A. Differential pressure of oxygen in venous blood
• B. Differential pressure of oxygen in arterial blood
• C. Differential pressure of oxygen in in tissue fluids
• D. Differential pressure of oxygen in in hemoglobin synthesis

Explanation: Carotid bodies primarily detect a fall in arterial oxygen partial pressure, especially when PaO₂ falls markedly, and then stimulate…

• A. Partial pressure of CO is less
• B. Bind avidly with Hb
• C. CO is less absorbed in water
• D. Alveolar membrane is less permeable

Explanation: Carbon monoxide binds haemoglobin very avidly, so capillary blood maintains an extremely low dissolved CO partial pressure and continued…

• A. 200 ML
• B. 400 ML
• C. 600 ML
• D. 800 ML

Explanation: Expired air is fully humidified in the airways, causing roughly 400 mL of water loss per day in a resting adult under ordinary conditions.

• A. Increased workload, decreasing duration of exercise
• B. Decreasing workload, increasing duration of exercise
• C. Increased workload, increasing duration of exercise
• D. Decreasing workload, decreasing duration of exercise

Explanation: At high altitude, reduced oxygen availability limits aerobic power, so work capacity is best maintained by lowering the workload and…

• A. is not affected by respiratory
• B. remains constant during exercise
• C. is inversely related to lung compliance
• D. decreased in lying posture

Explanation: When lung compliance is low, greater pressure and muscular effort are needed to produce the same tidal volume, so the elastic work of…

• A. Increased 2,3 BPG
• B. Increased temperature
• C. Increased concentration of carbon - di - oxide
• D. Increased concentration of oxygen

Explanation: Raised 2,3-BPG, temperature and carbon dioxide each reduce haemoglobin's oxygen affinity and shift the dissociation curve to the right.

• A. Increase in respiratory rate
• B. Increase in partial pressure of CO2
• C. Increase in oxygen carrying capacity of blood
• D. Increases in depth of respiration

Explanation: High altitude causes hyperventilation, with increased respiratory rate and depth, and later increases oxygen-carrying capacity through…

• A. It is secreted by Type II pneumocytes
• B. It contains lecithin and sphingomyelin
• C. It increases surface tension
• D. It prevents collapse of smaller alveoli

Explanation: Surfactant is secreted by type II pneumocytes and contains phospholipids including lecithin; it lowers surface tension and prevents small…

• A. Haldane effect
• B. Hamburger effect
• C. Breur effect
• D. Bohr effect

Explanation: The Bohr effect describes reduced haemoglobin affinity for oxygen when tissue CO2 and hydrogen ion concentration rise, promoting oxygen…

• A. Apex of lung
• B. Base of lung
• C. Posterior lobe of lung
• D. Middle lobe of lung

Explanation: The apex has relatively greater ventilation-perfusion ratio because perfusion decreases more sharply than ventilation toward the top of…

• A. Tidal volume
• B. Inspiratory reserve volume plus expiratory volume
• C. Tidal volume plus inspiratory reserve volume plus expiratory reserve volume
• D. Expiratory reserve volume plus reserve volume

Explanation: Vital capacity is the maximum volume expired after a maximal inspiration, so it equals tidal volume plus inspiratory reserve volume plus…

• A. Increased pH
• B. Hypothermia
• C. HbF
• D. Hypoxia

Explanation: Hypoxia decreases haemoglobin's oxygen affinity mainly through increased 2,3-BPG, shifting the dissociation curve to the right.

• A. Hypoxia
• B. Alkalosis
• C. Increased HbF
• D. Hypothermia

Explanation: Alkalosis, hypothermia and HbF increase haemoglobin's oxygen affinity by shifting the dissociation curve to the left.

• A. Dopamine metabolism
• B. Serotonin metabolism
• C. Adrenaline metabolism
• D. PGE2 production

Explanation: Pulmonary endothelial cells metabolise circulating serotonin, making serotonin clearance a recognised non-respiratory function of the…

• A. Ciliary motility
• B. Cellular hyperplasia
• C. Mucous secretion
• D. All of the above

Explanation: Smoking impairs ciliary movement and causes mucous gland or epithelial hyperplasia with increased mucus secretion.

• A. Herring - Breur reflex
• B. Bainbridge reflex
• C. Autonomic reflex
• D. Dynamic stretch reflex

Explanation: The Hering-Breuer inflation reflex is triggered by vagal stretch receptors during lung inflation and limits further inspiration.

• A. The relative proportion of reduced and oxygenated hemoglobin
• B. The absolute amount of reduced hemoglobin
• C. Thickness of the skin
• D. Fragility of capillaries

Explanation: Cyanosis becomes clinically apparent when the absolute amount of reduced haemoglobin rises to roughly 5 g/dL, rather than simply from a…

• A. Intrapulmonary pressure falls
• B. Intra thoracic pressure rises
• C. Intra-abdominal pressure rises
• D. The partial pressure of O2 in dead space rises

Explanation: During inspiration, intrapulmonary and intrathoracic pressures fall, while descent of the diaphragm raises intra-abdominal pressure.

• A. Decrease in arterial carbon dioxide level
• B. None of the above
• C. Increase in arterial oxygen level
• D. Increase in arterial carbon dioxide level

Explanation: An increase in arterial CO₂ raises hydrogen ion concentration in brain extracellular fluid and strongly stimulates the medullary…