Respiratory System Practice Questions

Q: Which of the following statements concerning alveolar macrophages is true?

They secrete elastase.. ### Explanation **Correct Option: B (They secrete elastase)** Alveolar macrophages (Dust cells) are the primary immune defense in the distal airways. When activated—particularly by irritants like cigarette smoke—they secrete various inflammatory mediators, including **elastase** (a matrix metalloproteinase). Elastase breaks down elastin, the protein responsible for the elastic recoil of the lungs. Under normal physiological conditions, this enzyme is neutralized by **$\alpha_1$-antitrypsin**. An imbalance between elastase and its inhibitor leads to the destruction of alveolar walls, resulting in **emphysema**. **Analysis of Incorrect Options:** * **Option A:** $\alpha_1$-antitrypsin is primarily synthesized and secreted by the **liver (hepatocytes)**, not macrophages. It serves as a protective protease inhibitor. * **Option C:** Alveolar macrophages originate from **blood monocytes**, which migrate into the lung tissue and differentiate. Neutrophils are different myeloid cells that are recruited to the lungs only during acute inflammation. * **Option D:** Hyaline membrane disease (Infant Respiratory Distress Syndrome) is caused by a **deficiency of surfactant** produced by **Type II pneumocytes**, not by macrophage activity. **High-Yield NEET-PG Pearls:** * **Protease-Antiprotease Hypothesis:** Emphysema is the result of excessive elastase (from macrophages and neutrophils) or deficient $\alpha_1$-antitrypsin. * **Smoking Effect:** Smoking increases the number of macrophages and inhibits the activity of $\alpha_1$-antitrypsin, accelerating lung tissue destruction. * **Heart Failure Cells:** In left-sided heart failure, alveolar macrophages that ingest extravasated RBCs and contain hemosiderin are called "Heart Failure Cells."

Q: When a normal subject develops a spontaneous pneumothorax of their right lung, which of the following would you expect to occur?

Right lung contracts. ### Explanation **1. Why the Correct Answer is Right:** The lungs and the chest wall are held together by the **negative intrapleural pressure** (typically -5 cm H₂O). This pressure acts as a "vacuum" that counteracts the natural elastic recoil of the lungs (which want to collapse inward) and the elastic recoil of the chest wall (which wants to expand outward). In a **spontaneous pneumothorax**, air enters the pleural space, equalizing the intrapleural pressure with atmospheric pressure. Once this negative pressure is lost, the lung’s inherent **elastic recoil** is unopposed, causing the **right lung to contract** or collapse toward the hilum. **2. Why the Other Options are Wrong:** * **B. Chest wall on the right contracts:** Incorrect. Because the chest wall’s natural tendency is to expand outward, the loss of negative intrapleural pressure allows the chest wall on the affected side to **expand** or move outward, not contract. * **C. Diaphragm on the right moves up:** Incorrect. The accumulation of air in the pleural space increases pressure, which typically pushes the diaphragm **downward** (flattening it) on the affected side. * **D. Mediastinum moves to the right:** Incorrect. In a pneumothorax, the increased pressure on the affected side (right) pushes the mobile mediastinum toward the **opposite side (left)**. This is most pronounced in a tension pneumothorax. **3. High-Yield Clinical Pearls for NEET-PG:** * **Resting Position:** At Functional Residual Capacity (FRC), the inward recoil of the lung exactly balances the outward recoil of the chest wall. * **Tension Pneumothorax:** Characterized by a "one-way valve" mechanism leading to rapid mediastinal shift, decreased venous return, and hypotension. This is a medical emergency requiring immediate needle decompression. * **Radiology:** Look for a "visceral pleural line" and the absence of peripheral lung markings on a chest X-ray.

Q: In the oxyhemoglobin dissociation curve, what is the corresponding oxygen tension in arterial blood for 95% oxygen saturation?

80 mm Hg. **Explanation:** The relationship between the partial pressure of oxygen ($PaO_2$) and the percentage of hemoglobin saturation ($SaO_2$) is represented by the **S-shaped (sigmoidal) Oxyhemoglobin Dissociation Curve**. This shape is due to the "cooperative binding" property of hemoglobin. **Why 80 mm Hg is correct:** In a healthy adult, a $PaO_2$ of **80 mm Hg** typically corresponds to an oxygen saturation ($SaO_2$) of approximately **95%**. This point lies on the upper "plateau" phase of the curve. In this region, even if the partial pressure of oxygen drops slightly (e.g., from 100 to 80 mm Hg), the hemoglobin remains highly saturated, ensuring adequate oxygen delivery to tissues. **Analysis of Incorrect Options:** * **90 mm Hg:** At this tension, the saturation is higher, approximately **97-98%**. * **70 mm Hg:** At this tension, the saturation begins to dip slightly below the 95% mark, usually around **93%**. * **60 mm Hg:** This is a critical "knee" point of the curve. At 60 mm Hg, the saturation is approximately **90%**. Below this level, the curve becomes very steep, meaning small drops in $PaO_2$ lead to large drops in $SaO_2$. **High-Yield NEET-PG Pearls:** 1. **$P_{50}$ Value:** The $PaO_2$ at which hemoglobin is 50% saturated is **26.6 mm Hg**. An increase in $P_{50}$ indicates a **Right Shift** (decreased affinity). 2. **Right Shift Factors (CADET, face Right!):** **C**O2 increase, **A**cidosis ($H^+$), 2,3-**D**PG increase, **E**xercise, and **T**emperature increase. 3. **The Plateau Phase:** Occurs above $PaO_2$ of 60 mm Hg; it acts as a safety buffer for oxygen loading in the lungs. 4. **The Steep Phase:** Occurs below 60 mm Hg; it facilitates the unloading of oxygen to the tissues.

Q: What is the V/Q ratio at the base of the lung?

0.6. **Explanation:** The Ventilation-Perfusion (V/Q) ratio is the ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli. In a standing individual, both ventilation (V) and perfusion (Q) increase from the apex to the base of the lung due to gravity. However, **perfusion increases much more steeply than ventilation.** At the **base of the lung**, there is a relative excess of perfusion compared to ventilation. While ventilation is high, the blood flow is even higher, leading to a **V/Q ratio of approximately 0.6** (less than 1). Conversely, at the **apex**, ventilation exceeds perfusion, resulting in a V/Q ratio of approximately **3.0**. **Analysis of Options:** * **Option A (1):** This represents the "ideal" V/Q ratio where ventilation and perfusion are perfectly matched, but this does not occur at the base. * **Option B (3):** This is the V/Q ratio at the **apex** of the lung, where perfusion is significantly lower due to gravitational effects. * **Option C (0.6):** **Correct.** This reflects the physiological state at the base where Q > V. * **Option D (1.8):** This is an intermediate value and does not represent the physiological ratio at either extreme of the lung. **High-Yield NEET-PG Pearls:** 1. **V/Q Gradient:** V/Q ratio is highest at the apex (~3.3) and lowest at the base (~0.6). 2. **Gas Exchange:** $P_{O2}$ is highest at the apex (due to high V/Q), while $P_{CO2}$ is highest at the base. 3. **Clinical Correlation:** Tuberculosis (TB) bacilli prefer the apex because of the high $P_{O2}$ (aerobic environment) resulting from the high V/Q ratio. 4. **West Zones:** The base of the lung typically corresponds to West Zone 3, where arterial and venous pressures exceed alveolar pressure.

Q: What is the partial pressure of oxygen in the expired air?

116 mm Hg. **Explanation:** The partial pressure of oxygen ($PO_2$) in **expired air** is approximately **116 mm Hg**. This value is a result of the mixing of two distinct air volumes during exhalation: 1. **Dead Space Air:** This air remains in the conducting zones (trachea, bronchi) and does not participate in gas exchange. Its $PO_2$ is similar to humidified inspired air (~149–150 mm Hg). 2. **Alveolar Air:** This air has undergone gas exchange, resulting in a lower $PO_2$ of approximately 100 mm Hg. When these two volumes mix during expiration, the resulting $PO_2$ (116 mm Hg) is higher than alveolar air but lower than atmospheric air. **Analysis of Incorrect Options:** * **Option B (158 mm Hg):** This is the $PO_2$ of **atmospheric (dry) air** at sea level. Once air is inspired and humidified in the upper airways, the $PO_2$ drops to ~149 mm Hg due to the addition of water vapor pressure. * **Option C (100 mm Hg):** This is the $PO_2$ of **alveolar air**. It is lower than inspired air because oxygen is constantly diffusing into the pulmonary capillaries. * **Option D (0.3 mm Hg):** This is the partial pressure of **Carbon Dioxide ($PCO_2$)** in atmospheric air. **NEET-PG High-Yield Pearls:** * **$PCO_2$ in Expired Air:** Approximately **27–32 mm Hg** (lower than alveolar $PCO_2$ of 40 mm Hg due to dilution with dead space air). * **Water Vapor Pressure:** At body temperature (37°C), it is always **47 mm Hg**. * **Alveolar Gas Equation:** $PAO_2 = FiO_2(P_{atm} - PH_2O) - (PaCO_2 / R)$. This is crucial for calculating the A-a gradient.

Q: In upper airway obstruction, all of the following changes are seen except?

RV decreased. In upper airway obstruction (UAO), the primary physiological challenge is increased resistance to airflow. This leads to characteristic changes in lung volumes and capacities. ### **Explanation of the Correct Answer** **Option B (RV decreased) is the correct "except" choice because Residual Volume (RV) actually increases or remains unchanged in airway obstruction.** In UAO, the increased resistance makes it difficult to exhale completely (air trapping). This leads to **hyperinflation**, which increases the Residual Volume (RV) and Functional Residual Capacity (FRC). Therefore, a decrease in RV is physiologically inconsistent with obstructive pathology. ### **Analysis of Incorrect Options** * **A. Decreased Maximum Breathing Capacity (MBC):** MBC (or MVV) is the most sensitive indicator of upper airway obstruction. Increased resistance significantly limits the volume of air that can be moved in and out of the lungs per minute. * **C. Decreased FEV1:** Obstruction increases airway resistance, which slows down the expiratory flow rate, leading to a reduction in Forced Expiratory Volume in 1 second (FEV1). * **D. Decreased Vital Capacity (VC):** While VC is primarily a measure of lung volume, in severe or chronic UAO, air trapping (increased RV) occurs at the expense of the Vital Capacity (since Total Lung Capacity remains relatively constant), leading to a decrease in VC. ### **High-Yield Clinical Pearls for NEET-PG** * **Flow-Volume Loops:** UAO is best diagnosed using flow-volume loops. * *Fixed obstruction:* Flattening of both inspiratory and expiratory limbs. * *Variable extrathoracic obstruction:* Flattening of the inspiratory limb only. * **FEV1/PEFR Ratio:** A ratio >10 mL/L/min (Empey’s Index) suggests upper airway obstruction rather than small airway disease (like asthma). * **Stridor:** The hallmark clinical sign of upper airway obstruction.

Question 1

High airway resistance is seen in which part of the respiratory system?

Accepted Answer

Main bronchus

Answer

Respiratory bronchiole

Answer

Terminal bronchiole

Answer

Intermediate bronchiole

Question 2

Which of the following statements concerning alveolar macrophages is true?

Accepted Answer

They secrete elastase.

Answer

They secrete a1-antitrypsin.

Answer

They originate from blood neutrophils.

Answer

They may play a role in causing hyaline membrane disease.

Question 3

When a normal subject develops a spontaneous pneumothorax of their right lung, which of the following would you expect to occur?

Accepted Answer

Right lung contracts

Answer

Chest wall on the right contracts

Answer

Diaphragm on the right moves up

Answer

Mediastinum moves to the right

Question 4

Hypoxemia in emphysema is due to all of the following except:

Accepted Answer

Anatomical dead space

Answer

Destruction of alveoli

Answer

Physiological dead space

Answer

Reduced elastic recoil

Question 5

In the oxyhemoglobin dissociation curve, what is the corresponding oxygen tension in arterial blood for 95% oxygen saturation?

Accepted Answer

80 mm Hg

Answer

90 mm Hg

Answer

60 mm Hg

Answer

70 mm Hg

Question 6

Which of the following is NOT seen in precapillary pulmonary hypertension?

Accepted Answer

Increased pulmonary wedge pressure

Answer

Increased pressure in pulmonary circulation

Answer

Increased capillary pressure

Answer

Right ventricular hypertrophy

Question 7

What is the V/Q ratio at the base of the lung?

Accepted Answer

0.6

Answer

1

Answer

3

Answer

1.8

Question 8

In the upright position, what happens to ventilation and perfusion from the apex to the base of the lung?

Accepted Answer

Ventilation increases, perfusion increases

Answer

Ventilation decreases, perfusion decreases

Answer

Ventilation decreases, perfusion increases

Answer

Ventilation increases, perfusion decreases

Question 9

What is the partial pressure of oxygen in the expired air?

Accepted Answer

116 mm Hg

Answer

158 mm Hg

Answer

100 mm Hg

Answer

0.3 mm Hg

Question 10

In upper airway obstruction, all of the following changes are seen except?

Accepted Answer

RV decreased

Answer

Decreased maximum breathing capacity

Answer

Decreased FEV1

Answer

Decreased vital capacity

Respiratory System — MCQs

Respiratory System — MCQs

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