Respiratory System Practice Questions

Q: Ventilation-perfusion ratio is maximum at which part of the lung?

Apex of the lung. **Explanation:** The Ventilation-Perfusion ratio (V/Q) is the ratio of the amount of air reaching the alveoli (V) to the amount of blood reaching the alveoli (Q). In a standing individual, gravity exerts a significant influence on both ventilation and blood flow, but the effect is much more pronounced on **perfusion**. 1. **Why the Apex is Correct:** Both ventilation and perfusion decrease as you move from the base to the apex. However, perfusion (Q) decreases much more sharply than ventilation (V) due to the low hydrostatic pressure in the pulmonary arteries at the top of the lung. Because the denominator (Q) decreases more than the numerator (V), the **V/Q ratio is highest at the apex** (approximately 3.0). 2. **Why the Base is Incorrect:** At the base of the lung, gravity increases both ventilation and perfusion. However, the increase in perfusion is disproportionately higher. This results in a **lower V/Q ratio** (approximately 0.6), making the base the most common site for "shunt-like" effects. 3. **Why Other Options are Incorrect:** The middle and posterior lobes follow the same gravitational gradient. In the upright position, the V/Q ratio progressively decreases from the superior (apex) to the inferior (base) segments. **High-Yield Facts for NEET-PG:** * **V/Q = 1:** The "ideal" ratio, usually found around the level of the 3rd rib. * **Apex (High V/Q):** Higher $P_AO_2$ (132 mmHg) and lower $P_ACO_2$ (28 mmHg). This high oxygen tension explains why **Mycobacterium tuberculosis** preferentially colonizes the apices. * **Base (Low V/Q):** Lower $P_AO_2$ and higher $P_ACO_2$. * **West Zones:** The apex corresponds to Zone 1 (potential dead space), while the base corresponds to Zone 3 (continuous flow).

Q: Which of the following is true about residual volume?

Cannot be measured directly with a spirometer. **Explanation:** **Residual Volume (RV)** is the volume of air remaining in the lungs after a maximal forced expiration. **Why Option C is correct:** Spirometry measures the volume of air that can be moved into or out of the lungs. Since RV can never be exhaled, it cannot be measured using a simple spirometer. To determine RV, indirect methods such as **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** (the most accurate) must be used. **Analysis of Incorrect Options:** * **Option A:** RV is the air left *after* the Expiratory Reserve Volume (ERV) has been exhaled. They are distinct components of the Functional Residual Capacity (FRC = ERV + RV). * **Option B:** Vital Capacity (VC) is the maximum volume of air a person can exhale after a maximum inhalation. It consists of TV + IRV + ERV. Since RV cannot be exhaled, it is **not** part of the Vital Capacity. * **Option D:** The "resting volume" of the lungs (the volume at the end of a normal quiet expiration) is the **Functional Residual Capacity (FRC)**, not RV. **High-Yield Clinical Pearls for NEET-PG:** * **Lung Capacities involving RV:** Any capacity that includes RV cannot be measured by spirometry. This includes **FRC** and **Total Lung Capacity (TLC)**. * **Obstructive vs. Restrictive:** RV is typically **increased** in obstructive diseases (like emphysema due to air trapping) and **decreased** in restrictive lung diseases (like pulmonary fibrosis). * **Closing Volume:** This is the volume at which small airways in the lower lobes begin to close; it is equal to RV plus a portion of the ERV.

Q: The pre-Bötzinger complex is a part of which respiratory center?

Ventral Respiratory Group (VRG). **Explanation:** The **pre-Bötzinger complex (pre-BötC)** is a small cluster of interneurons located in the ventrolateral medulla. It is considered the **pacemaker of respiration**, responsible for generating the basic respiratory rhythm. **1. Why Option A is Correct:** The pre-Bötzinger complex is anatomically and functionally a part of the **Ventral Respiratory Group (VRG)**. The VRG is a column of neurons in the medulla divided into three parts: the rostral VRG (containing the pre-BötC), the intermediate VRG, and the caudal VRG. While the VRG as a whole is primarily active during forceful breathing, the pre-BötC sub-region is essential for setting the basal rhythm of quiet breathing. **2. Why Incorrect Options are Wrong:** * **Option B (DRG):** The Dorsal Respiratory Group is located in the nucleus tractus solitarius (NTS). It primarily consists of inspiratory neurons and acts as the integration center for sensory input from the glossopharyngeal and vagus nerves. It does not contain the pacemaker cells. * **Option C & D:** Since the pre-BötC has a specific anatomical localization within the VRG, these options are incorrect. **High-Yield Clinical Pearls for NEET-PG:** * **Pacemaker Activity:** The pre-BötC contains G-protein coupled receptors; opioids (acting on $\mu$-receptors) inhibit these neurons, which is the mechanism behind **opioid-induced respiratory depression**. * **DRG vs. VRG:** Remember "D" for **D**orsal and **D**iaphragm (quiet inspiration), and "V" for **V**entral and **V**igorous (forced breathing). * **Pontine Centers:** The **Pneumotaxic center** (upper pons) limits inspiration (the "off-switch"), while the **Apneustic center** (lower pons) prolongs inspiration.

Q: What is false regarding emphysema?

Increased diffusion capacity. **Explanation:** Emphysema is a chronic obstructive pulmonary disease (COPD) characterized by the permanent enlargement of air spaces distal to the terminal bronchioles and the **destruction of alveolar walls**. **Why Option D is the Correct Answer:** The hallmark of emphysema is the destruction of the alveolar-capillary membrane. According to Fick’s Law, the rate of gas diffusion is directly proportional to the surface area available. In emphysema, the loss of septal walls significantly **decreases the surface area** for gas exchange, leading to a **decreased Diffusion Capacity (DLCO)**. Therefore, the statement "Increased diffusion capacity" is false. **Analysis of Incorrect Options:** * **A & B (Decreased FEV1 and Timed Vital Capacity):** Emphysema is an obstructive lung disease. Destruction of elastic tissue leads to loss of radial traction, causing small airway collapse during expiration. This results in increased airway resistance, significantly reducing the Forced Expiratory Volume in 1 second (FEV1) and the FEV1/FVC ratio (timed vital capacity). * **C (Increased Residual Volume):** Due to loss of elastic recoil and premature airway closure, air becomes trapped in the lungs (air trapping). This leads to hyperinflation, which increases the Residual Volume (RV) and Total Lung Capacity (TLC). **High-Yield Clinical Pearls for NEET-PG:** * **Compliance:** Emphysema is characterized by **increased lung compliance** due to the loss of elastic fibers. * **Pink Puffers:** Patients are often thin, distressed, and use pursed-lip breathing to maintain airway pressure. * **DLCO:** This is the most useful test to differentiate emphysema (low DLCO) from chronic bronchitis or asthma (often normal DLCO). * **Chest X-ray:** Look for flattened diaphragms and increased retrosternal space.

Q: What is the cause of unilateral diaphragmatic paralysis?

Decrease in inspiratory reserve volume. **Explanation:** Unilateral diaphragmatic paralysis occurs due to the dysfunction of one phrenic nerve (C3-C5). Since the diaphragm is the primary muscle of inspiration, its paralysis leads to a restrictive ventilatory defect. **Why the correct answer is right:** In unilateral paralysis, the affected side of the diaphragm fails to descend and may even move paradoxically upward (cephalad) during inspiration due to negative intrathoracic pressure. This significantly limits the expansion of the thoracic cavity, leading to a **decrease in Inspiratory Reserve Volume (IRV)** and Inspiratory Capacity (IC). Because the lung cannot expand fully, the volume of air that can be inspired above a normal tidal breath is markedly reduced. **Analysis of Incorrect Options:** * **A. No change in Total Lung Capacity (TLC):** Incorrect. TLC **decreases** (typically by 15-25%) because the total volume of gas contained in the lungs at full inspiration is restricted by the elevated, non-functional hemidiaphragm. * **B. Increase in Forced Vital Capacity (FVC):** Incorrect. FVC **decreases**. Restrictive lung pathologies always lead to a reduction in vital capacity as the bellows function of the chest is compromised. * **D. No change in Maximum Breathing Capacity (MBC):** Incorrect. MBC (or MVV - Maximum Voluntary Ventilation) **decreases** significantly because the patient cannot sustain high-volume, rapid breathing due to the mechanical disadvantage of the paralyzed muscle. **Clinical Pearls for NEET-PG:** * **Radiology:** The "Sniff Test" (fluoroscopy) is the gold standard, showing **paradoxical movement** of the paralyzed dome. * **Positioning:** Dyspnea and lung volumes worsen in the **supine position** because abdominal contents push the paralyzed diaphragm further into the thorax. * **Etiology:** The most common cause is malignancy (bronchogenic carcinoma) involving the phrenic nerve, followed by trauma or idiopathic causes.

Q: Haemoglobin is the major buffer in blood. Bicarbonate ions diffuse out of erythrocytes into plasma in exchange for which ion?

Chloride ion. This question tests the understanding of the **Chloride Shift (Hamburger Phenomenon)**, a vital mechanism for CO₂ transport and acid-base balance. ### Explanation of the Correct Answer When CO₂ enters erythrocytes, it reacts with water (catalyzed by carbonic anhydrase) to form carbonic acid, which dissociates into **H⁺** and **HCO₃⁻**. 1. The H⁺ ions are buffered by deoxyhemoglobin. 2. As HCO₃⁻ (bicarbonate) concentrations rise, they diffuse out of the cell into the plasma along a concentration gradient. 3. To maintain **electrical neutrality**, an equivalent amount of negative charge must enter the cell. This is achieved by the influx of **Chloride ions (Cl⁻)** via the **Anion Exchanger 1 (Band 3 protein)**. This process is the Chloride Shift. ### Why Other Options are Incorrect * **A. Potassium:** Potassium is the primary intracellular cation. While it maintains osmotic balance, it does not exchange directly for bicarbonate during CO₂ transport. * **B. Phosphate:** Intracellular phosphates act as buffers, but they do not participate in the rapid transmembrane exchange required for systemic CO₂ transport. * **C. Carbonic acid:** This is an intermediate molecule (H₂CO₃) that quickly dissociates; it does not exist as a transportable ion in this exchange. ### High-Yield NEET-PG Pearls * **Reverse Chloride Shift:** Occurs in the **lungs**, where Cl⁻ moves *out* of the RBC and HCO₃⁻ moves *in* to be converted back to CO₂ for exhalation. * **Water Movement:** When Cl⁻ enters the RBC (in systemic tissues), osmotic pressure increases, causing water to enter the cell. Consequently, **venous RBCs are slightly larger (higher MCV)** than arterial RBCs. * **Haldane Effect:** Deoxygenation of blood increases its ability to carry CO₂, primarily because deoxyhemoglobin is a better buffer for H⁺ than oxyhemoglobin.

Question 1

Which of the following is FALSE regarding pulmonary circulation?

Accepted Answer

Vital capacity decreases when assuming a supine position.

Answer

The V/Q ratio at rest is approximately 0.8.

Answer

Ventilation is typically less at the apex than at the base of the lung.

Answer

All of the above are true.

Question 2

Ventilation-perfusion ratio is maximum at which part of the lung?

Accepted Answer

Apex of the lung

Answer

Base of the lung

Answer

Posterior lobe of the lung

Answer

Middle of the lung

Question 3

Which of the following conditions is characterized by thickening of the respiratory membrane?

Accepted Answer

Pneumonia

Answer

Bronchiectasis

Answer

Good-pasture syndrome

Answer

Henoch-Schönlein purpura (HSP)

Question 4

Which of the following is true about residual volume?

Accepted Answer

Cannot be measured directly with a spirometer

Answer

Part of the expiratory reserve volume

Answer

Part of the vital capacity

Answer

Represents the resting volume of the lungs

Question 5

The alveolar-arterial O2 tension gradient increases in which of the following conditions?

Accepted Answer

Hypoventilation

Answer

Right to left shunt

Answer

Diffusion defect

Answer

Ventilation-perfusion abnormality

Question 6

The pre-Bötzinger complex is a part of which respiratory center?

Accepted Answer

Ventral Respiratory Group (VRG)

Answer

Dorsal Respiratory Group (DRG)

Answer

Both VRG and DRG

Answer

Neither VRG nor DRG

Question 7

What is false regarding emphysema?

Accepted Answer

Increased diffusion capacity

Answer

Decreased FEV1

Answer

Decreased timed vital capacity

Answer

Increased residual volume

Question 8

What is the cause of unilateral diaphragmatic paralysis?

Accepted Answer

Decrease in inspiratory reserve volume

Answer

No change in total lung capacity

Answer

Increase in forced vital capacity

Answer

No change in maximum breathing capacity

Question 9

Which of the following is NOT a cause of a rightward shift of the oxygen-hemoglobin dissociation curve?

Accepted Answer

Hypokalemia

Answer

Hyperkalemia

Answer

Anemia

Answer

Metabolic alkalosis

Question 10

Haemoglobin is the major buffer in blood. Bicarbonate ions diffuse out of erythrocytes into plasma in exchange for which ion?

Accepted Answer

Chloride ion

Answer

Potassium

Answer

Phosphate

Answer

Carbonic acid

Respiratory System — MCQs

Respiratory System — MCQs

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