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Respiratory System: Mixed Bag MCQs
Section 1: Mechanism, Pressures, and Compliance
1. During normal quiet inspiration, which of the following events occurs? A. Alveolar pressure rises above atmospheric pressure. B. The diaphragm relaxes and moves upward. C. Intrapleural pressure becomes more negative. D. The process is entirely passive.
2. A 25-year-old male presents with a stab wound to the chest resulting in a pneumothorax. In this condition, the intrapleural pressure becomes: A. More negative than normal. B. Equal to atmospheric pressure. C. Highly positive throughout the cycle. D. Unchanged.
3. Which of the following is responsible for the "Hysteresis" observed in a pressure-volume curve of the lung? A. Airway resistance. B. Alveolar surface tension and surfactant dynamics. C. The presence of residual volume. D. Elastic recoil of the chest wall.
4. According to the Law of Laplace (P=2T/r), if two alveoli have the same surface tension but different radii, the smaller alveolus will: A. Have a lower collapsing pressure. B. Have a higher collapsing pressure. C. Expand more easily. D. Be more compliant.
5. Pulmonary surfactant increases lung compliance by: A. Increasing the work of breathing. B. Reducing the surface tension of the fluid lining the alveoli. C. Increasing the elastic recoil of the lung. D. Constricting the bronchioles.
6. In a patient with Pulmonary Fibrosis, which change is expected in the lung compliance curve? A. The curve shifts upward and to the left (increased compliance). B. The curve shifts downward and to the right (decreased compliance). C. The slope of the curve increases. D. FRC is significantly increased.
7. Which muscle is primarily responsible for active, forced expiration? A. Diaphragm. B. External intercostals. C. Internal intercostals and abdominal muscles. D. Sternocleidomastoid.
Section 2: Lung Volumes and Capacities
8. Which of the following cannot be measured by a simple student spirometer? A. Vital Capacity (VC). B. Tidal Volume (TV). C. Functional Residual Capacity (FRC). D. Inspiratory Capacity (IC).
9. Calculate the Vital Capacity (VC) given: TV=500 mL, IRV=2500 mL, ERV=1100 mL, RV=1200 mL. A. 3000 mL. B. 4100 mL. C. 5300 mL. D. 3600 mL.
10. Functional Residual Capacity (FRC) represents the equilibrium volume of the lungs where: A. Alveolar pressure is maximum. B. The collapsing force of the lungs is balanced by the expanding force of the chest wall. C. Intrapleural pressure is zero. D. All respiratory muscles are maximally contracted.
11. A patient has a TV of 500 mL and a breathing rate of 12/min. If the anatomical dead space is 150 mL, what is the Alveolar Ventilation? A. 6000 mL/min. B. 4200 mL/min. C. 1800 mL/min. D. 5850 mL/min.
12. In Obstructive Lung Diseases like Asthma, which of the following is typically decreased? A. Total Lung Capacity (TLC). B. FEV
1
/FVC ratio. C. Residual Volume (RV). D. Functional Residual Capacity (FRC).
13. The Bohr Effect explains the shift in the oxygen-hemoglobin dissociation curve due to changes in: A. 2,3-DPG. B. Temperature. C. PCO
2
and pH. D. Exercise.
Section 3: Gas Transport and Exchange
14. Most of the carbon dioxide (CO
2
) is transported in the blood in the form of: A. Dissolved CO
2
. B. Carbaminohemoglobin. C. Bicarbonate ions (HCO
3
−
). D. Carbonic acid.
15. The "Chloride Shift" (Hamburger Phenomenon) in systemic tissues involves the movement of: A. Cl
−
into the RBC and HCO
3
−
out of the RBC. B. Cl
−
out of the RBC and HCO
3
−
into the RBC. C. Na
+
and Cl
−
into the RBC. D. H
+
out of the RBC.
16. Which of the following causes a RIGHT shift of the Oxygen-Hemoglobin Dissociation Curve (decreased affinity)? A. Decreased Temperature. B. Increased pH (Alkalosis). C. Increased 2,3-DPG concentration. D. Carbon Monoxide poisoning.
17. If a patient’s Hemoglobin is 15 g/dL, what is the maximum oxygen-carrying capacity of their blood? (Assume 1 g Hb binds 1.34 mL O
2
) A. 15 mL/dL. B. 20.1 mL/dL. C. 13.4 mL/dL. D. 40 mL/dL.
18. In perfusion-limited oxygen exchange, equilibration of PO
2
between alveoli and capillaries occurs within: A. The last one-third of the capillary length. B. The first one-third of the capillary length. C. Only during heavy exercise. D. It never equilibrates.
19. Carbon Monoxide (CO) poisoning is particularly dangerous because it: A. Increases the P
50
value. B. Competes for O
2
binding sites and shifts the curve to the left, hindering O
2
unloading. C. Decreases the solubility of O
2
in plasma. D. Stimulates peripheral chemoreceptors to cause hyperventilation.
Section 4: Regulation of Respiration
20. The primary stimulus for Central Chemoreceptors is: A. Low Arterial PO
2
(<60 mmHg). B. High Arterial PCO
2
(via H
+
in CSF). C. Lactic acid in the blood. D. High Arterial pH.
21. The "Pneumotaxic Center" is located in the ________ and its function is to ________. A. Medulla; stimulate inspiration. B. Upper Pons; limit the duration of inspiration. C. Lower Pons; prolong inspiration. D. Medulla; control expiration.
22. Which group of neurons is responsible for the basic rhythm of spontaneous breathing? A. Ventral Respiratory Group (VRG). B. Dorsal Respiratory Group (DRG). C. Apneustic Center. D. Cerebral Cortex.
23. The Hering-Breuer Inflation Reflex is initiated by: A. Lung stretch receptors. B. Central chemoreceptors. C. Irritant receptors. D. J-receptors.
24. In the "Tug-of-War" during respiratory failure, why does a patient often present with tachycardia despite the primary chemoreceptor reflex favoring bradycardia? A. Direct stimulation of the SA node by CO
2
. B. Secondary reflex due to hyperventilation and lung stretch inhibiting the vagal center. C. Baroreceptor reflex being hyperactive. D. Lack of acetylcholine at the heart.
Section 5: V/Q Ratio and Regional Variations
25. In a standing person, compared to the base of the lung, the apex has a: A. Higher V/Q ratio. B. Lower PO
2
. C. Higher blood flow. D. Higher ventilation rate.
26. A V/Q ratio of zero indicates: A. Dead space (ventilation without perfusion). B. A physiological shunt (perfusion without ventilation). C. Ideal gas exchange. D. High altitude adaptation.
27. In Pulmonary Embolism, the affected region of the lung behaves as: A. A shunt. B. Physiological dead space (V/Q=infinity). C. A site of increased O
2
diffusion. D. A region with a V/Q of 0.8.
Section 6: Hypoxia and Environmental Changes
28. Which type of hypoxia is characterized by normal arterial PO
2
but decreased oxygen-carrying capacity? A. Hypoxemic Hypoxia. B. Anemic Hypoxia. C. Stagnant Hypoxia. D. Histotoxic Hypoxia.
29. At high altitudes, the immediate hyperventilation is caused by: A. Stimulation of central chemoreceptors by low CO
2
. B. Stimulation of peripheral chemoreceptors by low arterial PO
2
. C. Increased blood pH. D. Increased 2,3-DPG.
30. Acclimatization to high altitude involves all the following EXCEPT: A. Increased red blood cell count (polycythemia). B. Increased 2,3-DPG levels. C. Shift of the O
2
-Hb dissociation curve to the left. D. Renal excretion of bicarbonate to correct alkalosis.
31. In deep-sea diving, the risk of "Nitrogen Narcosis" occurs because: A. Nitrogen becomes more soluble in body fats at high pressure. B. Oxygen becomes toxic. C. Carbon dioxide is retained. D. Hemoglobin affinity for O
2
increases.
32. "The Bends" or Decompression Sickness is caused by: A. Rapid ascent leading to nitrogen bubbles forming in tissues and blood. B. Slow ascent. C. High PO
2
in the lungs. D. Increased lung compliance.
Section 7: Case Scenarios and Calculations
33. Case: A 60-year-old heavy smoker presents with a barrel chest and dyspnea. His FEV
1
is 1.2 L and FVC is 3.0 L. What is his FEV
1
/FVC ratio and the likely diagnosis? A. 40%; Restrictive disease. B. 40%; Obstructive disease (Emphysema). C. 75%; Normal. D. 90%; Fibrosis.
34. Calculate the Dead Space volume (V
D
) if TV=500 mL, Arterial PCO
2
=40 mmHg, and Mixed Expired PCO
2
=28 mmHg. A. 100 mL. B. 150 mL. C. 200 mL. D. 300 mL.
35. A climber at the base camp of Mt. Everest (P
B
=400 mmHg) breathes air. What is the PO
2
of the inspired dry air? A. 160 mmHg. B. 84 mmHg. C. 100 mmHg. D. 40 mmHg.
36. A patient in the ICU has a right-to-left shunt. If they are given 100% oxygen to breathe: A. Arterial PO
2
will immediately rise to 600 mmHg. B. Arterial PO
2
will show only a modest increase. C. Hemoglobin affinity for O
2
will decrease. D. The shunt will be abolished.
37. Which of the following describes "Kussmaul Breathing"? A. Periodic waxing and waning of breaths. B. Rapid, deep "hissing" breaths seen in metabolic acidosis. C. Temporary stoppage of breathing during swallowing. D. Shallow breaths with prolonged pauses.
38. In "Locked-in Syndrome," where is the lesion typically located? A. Medulla. B. Ventral Pons. C. Cerebral Cortex. D. Cerebellum.
39. Carbonic Anhydrase is essential in the lungs for: A. Binding CO
2
to Hemoglobin. B. Rapid conversion of HCO
3
−
and H
+
back into CO
2
and H
2
O. C. Pumping chloride out of cells. D. Reducing surface tension.
40. The A-a gradient is INCREASED in which of the following? A. Hypoventilation. B. High altitude. C. Diffusion defects (e.g., Fibrosis). D. Breathing 10% oxygen.
--------------------------------------------------------------------------------
Answer Key and Explanations
C. During inspiration, thoracic volume increases, causing P
IP
to become more negative (from −5 to −8 cm H
2
O) to pull the lungs open.
B. Pneumothorax breaks the seal; air enters the intrapleural space, and pressure equilibrates with atmospheric pressure (zero), allowing the lung to collapse.
B. Hysteresis is the difference between inflation and deflation limbs, caused primarily by the energy needed to overcome surface tension at the air-liquid interface.
B. Small alveoli have smaller radii; thus, the pressure required to keep them open is higher, making them prone to collapse without surfactant.
B. Surfactant reduces surface tension more effectively in smaller alveoli, preventing collapse and making the lung easier to inflate (increased compliance).
B. Fibrosis makes the lungs "stiff." Lower volume is achieved for the same pressure, shifting the curve down/right.
C. Normal expiration is passive (elastic recoil), but forced expiration requires the internal intercostals and abdominal muscles to compress the thorax.
C. Spirometry cannot measure RV (Residual Volume). Since FRC=ERV+RV, it also cannot be measured directly.
B. VC=TV+IRV+ERV→500+2500+1100=4100 mL. RV is not included in VC.
B. At FRC, the inward elastic recoil of the lungs and the outward spring of the chest wall are equal and opposite.
B. Alveolar Ventilation =(TV−Dead Space)×Rate→(500−150)×12=350×12=4200 mL/min.
B. In obstructive disease, FEV
1
falls much more than FVC, leading to a low ratio (<70%).
C. Bohr effect specifically refers to the reduced affinity of Hb for O
2
in the presence of high H
+
(acid) and CO
2
.
C. Approximately 70–90% of CO
2
is transported as bicarbonate in the plasma.
A. In tissues, HCO
3
−
produced in RBCs moves out into plasma; to maintain electrical neutrality, Cl
−
moves into the RBC.
C. Increased 2,3-DPG reduces Hb affinity for O
2
, helping tissues extract more O
2
(Right Shift).
B. 15 g/dL×1.34 mL/g=20.1 mL O
2
per 100 mL blood.
B. Oxygen is highly soluble and binds Hb; normally, it equilibrates with alveolar gas very quickly within the first 1/3 of capillary transit.
B. CO binds to Hb with 200x affinity of O
2
and prevents the other three sites from releasing O
2
to tissues (Left shift).
B. Central chemoreceptors detect pH changes in the CSF. Since H
+
can't cross the blood-brain barrier but CO
2
can, arterial PCO
2
is the primary driver.
B. The pneumotaxic center in the upper pons acts as an "off-switch" for the inspiratory ramp, limiting TV and increasing rate.
B. The DRG contains mainly inspiratory neurons that generate the basic rhythm.
A. When the lungs are over-inflated, stretch receptors send signals via the Vagus nerve to inhibit further inspiration.
B. Although the chemoreflex causes bradycardia, the mechanical effect of hyperventilation and the lung-inflation reflex usually dominate, causing tachycardia.
A. Blood flow (Q) falls faster than ventilation (V) as we move from base to apex; thus, V/Q is highest at the apex (∼3.0).
B. V/Q=0 means ventilation is zero; blood passes through without getting oxygenated (Shunt).
B. V/Q=infinity means perfusion is zero; ventilation is "wasted" because there is no blood to pick up the gas.
B. In anemia, PO
2
is normal, but because there is less Hb, the total O
2
content is low.
B. Low PO
2
(<60 mmHg) at altitude is the major drive for peripheral chemoreceptors to initiate hyperventilation.
C. Acclimatization causes a RIGHT shift (increased 2,3-DPG) to facilitate O
2
unloading at tissues.
A. At high partial pressures in deep sea, N
2
dissolves in the lipid-rich myelin sheath of neurons, acting like an anesthetic.
A. When a diver rises too fast, N
2
comes out of solution rapidly, forming bubbles that block capillaries and cause pain.
B. 1.2/3.0=40%. The low ratio plus the "barrel chest" description points to obstructive disease (COPD/Emphysema).
B. Bohr Equation: V
D
=TV×(PaCO
2
−PECO
2
)/PaCO
2
→500×(40−28)/40=500×0.3=150 mL.
B. PO
2
=Fractional concentration×Total Pressure→0.21×400=84 mmHg.
B. In a shunt, the blood completely bypasses ventilated alveoli. Adding 100% Oxygen to the ventilated part doesn't help the shunted blood.
B. Kussmaul breathing is the respiratory compensation for metabolic acidosis (e.g., diabetic ketoacidosis), characterized by deep, rapid breaths.
B. Locked-in syndrome is usually caused by a stroke in the ventral pons, sparing the RAS (consciousness) but destroying motor tracts.
B. In the pulmonary capillaries, CA is needed to quickly convert HCO
3
−
back to CO
2
so it can be exhaled.
C. A-a gradient increases in shunts, V/Q mismatch, and diffusion defects (Fibrosis) because O
2
can't equilibrate properly.
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