Respiratory System Practice Questions

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: 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: A healthy 30-year-old male runs on the treadmill for 30 minutes. Which of the following muscles are primarily used during expiration?

Internal intercostals and abdominal recti. **Explanation:** The key to answering this question lies in distinguishing between **quiet breathing** and **forced (active) breathing**. 1. **Why Option C is Correct:** In a healthy individual at rest, expiration is a **passive process** resulting from the elastic recoil of the lungs. However, during exercise (like running on a treadmill), ventilation increases, and expiration becomes an **active process**. * **Abdominal Recti:** These are the most important muscles for forced expiration. They contract to push the abdominal contents upward against the diaphragm, forcefully decreasing the thoracic volume. * **Internal Intercostals:** These muscles pull the rib cage downward and inward (depressing the ribs), further decreasing the thoracic dimensions. 2. **Analysis of Incorrect Options:** * **Option A & B (Diaphragm):** The diaphragm is the primary muscle of **inspiration**. While it relaxes during expiration, it does not "drive" the expiratory phase. * **Option A & D (Sternocleidomastoid):** This is an **accessory muscle of inspiration**. It helps lift the sternum upward during deep or labored breathing (e.g., respiratory distress) to increase thoracic volume. 3. **NEET-PG High-Yield Pearls:** * **Primary Muscle of Quiet Inspiration:** Diaphragm (contributes ~75% of air movement). * **Accessory Muscles of Inspiration:** Sternocleidomastoid (lifts sternum), Scalene (lifts first two ribs), and External Intercostals. * **Active Expiration:** Occurs during exercise, coughing, sneezing, or in obstructive pathologies like COPD/Asthma. * **Bucket Handle Movement:** Mediated by external intercostals (increases transverse diameter). * **Pump Handle Movement:** Mediated by the sternum/upper ribs (increases anteroposterior diameter).

Q: All of the following muscles are involved in inspiration except?

Internal intercostal muscle. **Explanation:** The mechanics of breathing depend on the coordinated contraction of specific muscle groups to alter thoracic volume. **1. Why the Correct Answer is Right:** The **Internal Intercostal muscles** (specifically the interosseous portion) are primarily **muscles of expiration**. When they contract, they pull the ribs downward and inward, decreasing the transverse and anteroposterior diameters of the thorax. This increases intrapulmonary pressure, forcing air out of the lungs. Note: The *external* intercostals are inspiratory, while *internal* are expiratory (Mnemonic: **Ex**ternal = **In**spiration; **In**ternal = **Ex**piration). **2. Why the Other Options are Wrong:** * **Diaphragm (Option C):** This is the **primary muscle of inspiration**, responsible for about 75% of air movement during quiet breathing. Its contraction increases the vertical dimension of the thoracic cavity. * **Scalene (Option A) & Sternocleidomastoid (Option D):** These are **accessory muscles of inspiration**. The scalene muscles elevate the first two ribs, while the sternocleidomastoid elevates the sternum. They are typically recruited during deep breathing or respiratory distress to further expand the thoracic cage. **Clinical Pearls for NEET-PG:** * **Quiet Breathing:** Inspiration is an **active** process (requires muscle contraction), while quiet expiration is a **passive** process (due to elastic recoil of the lungs). * **Forced Expiration:** This is an **active** process involving the **Abdominal muscles** (Rectus abdominis, Obliques) and Internal intercostals. * **Nerve Supply:** The Diaphragm is supplied by the Phrenic nerve (C3, C4, C5). "C3, 4, 5 keep the diaphragm alive."

Q: Which of the following conditions can cause hypoxemia?

All of the above. **Explanation:** Hypoxemia is defined as a decrease in the partial pressure of oxygen in arterial blood ($PaO_2$). It is caused by five primary physiological mechanisms: **Hypoventilation, V/Q Mismatch, Right-to-Left Shunt, Diffusion Impairment, and Low Inspired Oxygen ($FiO_2$).** * **Hypoventilation (Option A):** When the rate of alveolar ventilation decreases, $CO_2$ accumulates in the alveoli. According to the Alveolar Gas Equation, as $PACO_2$ rises, $PAO_2$ must fall, leading to hypoxemia. * **Myasthenia Gravis (Option B):** This is a neuromuscular junction disorder that leads to weakness of the respiratory muscles (diaphragm and intercostals). This results in **Type II Respiratory Failure** characterized by hypoventilation, thereby causing hypoxemia. * **Pulmonary Emboli (Option C):** An embolus obstructs blood flow to a portion of the lung. This creates areas that are ventilated but not perfused, leading to a **Ventilation-Perfusion (V/Q) Mismatch** (specifically, an increase in physiological dead space). This is one of the most common clinical causes of hypoxemia. **High-Yield Clinical Pearls for NEET-PG:** 1. **A-a Gradient:** This is the key to differentiating causes. The A-a gradient is **normal** in Hypoventilation and Low $FiO_2$, but **increased** in V/Q Mismatch, Shunt, and Diffusion impairment. 2. **Oxygen Response:** Hypoxemia caused by a **Right-to-Left Shunt** is the only type that does not significantly improve with 100% supplemental oxygen. 3. **V/Q Ratios:** In a standing position, both ventilation and perfusion are highest at the **base** of the lung, but the V/Q ratio is highest at the **apex**.

Question 1

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 2

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 3

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 4

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 5

A healthy 30-year-old male runs on the treadmill for 30 minutes. Which of the following muscles are primarily used during expiration?

Accepted Answer

Internal intercostals and abdominal recti

Answer

Sternocleidomastoid and Diaphragm

Answer

Diaphragm and Internal intercostals

Answer

Sternocleidomastoid

Question 6

All of the following muscles are involved in inspiration except?

Accepted Answer

Internal intercostal muscle

Answer

Scalene

Answer

Diaphragm

Answer

Sternocleidomastoid

Question 7

What is true regarding the physiology of surfactant?

Accepted Answer

SP-A plays a major role in the innate host defense of the lung.

Answer

SP-A and SP-D are hydrophobic, and SP-B and SP-D are hydrophilic.

Answer

Surfactant is secreted into the alveolar lumen as tubular myelin.

Answer

Pulmonary surfactant is composed of 80% lipids and 20% proteins.

Question 8

Regarding dead space volume in a normal individual, which of the following statements is true?

Accepted Answer

Anatomical dead space is less than physiological dead space.

Answer

Anatomical dead space is greater than physiological dead space.

Answer

Anatomical dead space is equal to physiological dead space.

Answer

Anatomical dead space is not related to physiological dead space.

Question 9

Which of the following conditions can cause hypoxemia?

Accepted Answer

All of the above

Answer

Hypoventilation

Answer

Myasthenia gravis

Answer

Pulmonary emboli

Question 10

Which parameter best denotes airway resistance?

Accepted Answer

Mid respiratory flow rates

Answer

Vital Capacity

Answer

FEV1

Answer

Total volume

Respiratory System — MCQs

Respiratory System — MCQs

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