Respiratory System Practice Questions

Q: Which factor most affects the oxygen-carrying capacity of blood?

Hemoglobin. **Explanation:** The **oxygen-carrying capacity** of blood is defined as the maximum amount of oxygen that can be carried by a given volume of blood. This is primarily determined by the concentration of **Hemoglobin (Hb)**. **Why Hemoglobin is correct:** Each gram of pure hemoglobin can bind approximately **1.34 mL of oxygen** (Hüfner's constant). Since about 98-99% of oxygen in the blood is transported bound to hemoglobin (with only 1-2% dissolved in plasma), the total amount of oxygen the blood can hold is directly proportional to the hemoglobin concentration. The formula for Oxygen Content is: $(1.34 \times \text{Hb} \times \text{SaO}_2) + (0.003 \times \text{PaO}_2)$. **Why other options are incorrect:** * **pH and pCO2:** These factors influence the **Oxygen-Hemoglobin Dissociation Curve (OHDC)** and hemoglobin’s *affinity* for oxygen (Bohr Effect). While they determine how easily oxygen is loaded or unloaded, they do not change the total capacity of the blood to carry oxygen. * **Red blood cell count:** While RBCs contain hemoglobin, the count itself is not the direct measure of capacity. For example, in microcytic anemia, the RBC count might be normal or high, but the oxygen-carrying capacity is reduced because the total hemoglobin content is low. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Oxygen Capacity:** In a healthy adult with 15g/dL of Hb, the capacity is approximately **20.1 mL O2/100mL** of blood. * **Anemia vs. CO Poisoning:** In both conditions, the oxygen-carrying capacity is **decreased**, but the PaO2 (dissolved oxygen) remains normal. * **Methemoglobinemia:** Reduces oxygen-carrying capacity because iron is in the ferric state ($Fe^{3+}$), which cannot bind oxygen.

Q: Which of the following functions is associated with bronchial circulation?

Air conditioning of inhaled air. **Explanation:** The lungs have a dual blood supply: the **pulmonary circulation** (for gas exchange) and the **bronchial circulation** (the systemic nutritional supply). **1. Why Option A is Correct:** The bronchial circulation arises from the systemic arteries (aorta) and supplies the conducting airways down to the terminal bronchioles. One of its primary physiological roles is **air conditioning**. As air travels through the conducting zone, the extensive subepithelial capillary network of the bronchial vessels warms and humidifies the inhaled air to body temperature and 100% humidity before it reaches the delicate alveoli. **2. Why Other Options are Incorrect:** * **B. Drug absorption:** While some absorption occurs, it is not a primary physiological *function* of bronchial circulation. Most inhaled drugs are designed for local action or absorbed via the vast surface area of the pulmonary capillaries. * **C. Gaseous exchange:** This is the primary function of the **pulmonary circulation**. The bronchial circulation is "non-respiratory" as it supplies oxygenated blood to the tissues rather than picking up oxygen from the alveoli. * **D. Reserve volume:** This is a static lung volume (ERV) related to pulmonary mechanics and ventilation, not a function of the vascular supply. **Clinical Pearls & High-Yield Facts:** * **Bronchial Shunt:** About 1%–2% of the total cardiac output goes to the bronchial circulation. Most of this blood drains into the pulmonary veins (rather than the right atrium), contributing to the **physiological shunt** (venous admixture). * **Hemoptysis:** In cases of massive hemoptysis (e.g., in Bronchiectasis or TB), the bleeding usually originates from the high-pressure **bronchial arteries**, not the low-pressure pulmonary arteries. * **Nutritional Role:** It supplies the visceral pleura, large blood vessels, and the tracheobronchial tree.

Q: What is the respiratory quotient on a mixed diet?

0.85. **Explanation:** The **Respiratory Quotient (RQ)** is the ratio of the volume of carbon dioxide ($CO_2$) produced to the volume of oxygen ($O_2$) consumed per unit of time ($RQ = CO_2 \text{ produced} / O_2 \text{ consumed}$). It reflects the type of fuel being metabolized by the body. **Why 0.85 is correct:** The RQ varies depending on the substrate being oxidized: * **Carbohydrates:** $RQ = 1.0$ (Equal $O_2$ consumed and $CO_2$ produced). * **Proteins:** $RQ \approx 0.8$. * **Fats:** $RQ \approx 0.7$ (Require more $O_2$ for oxidation relative to $CO_2$ produced). On a **mixed diet** (a typical combination of carbohydrates, proteins, and fats), the average RQ is approximately **0.82 to 0.85**. Therefore, option C is the most accurate representation of a standard physiological state. **Analysis of Incorrect Options:** * **A (0.1) & B (0.33):** These values are physiologically impossible for human metabolism. An RQ below 0.7 is rarely seen except in states of extreme starvation or specific metabolic disorders (like ketogenesis), but even then, it does not drop to 0.1 or 0.33. * **D (0.91):** This value is higher than the average mixed diet. It would indicate a diet very high in carbohydrates or a state of hyperventilation (where $CO_2$ is "blown off" excessively). **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Exchange Ratio (RER):** While RQ is measured at the cellular level, RER is measured at the mouth using expired gases. In steady-state, $RQ = RER$. * **Hyperventilation:** Increases RER (can go $>1.0$) because $CO_2$ is eliminated faster than it is produced. * **Metabolic Acidosis:** Also increases RER as buffering of $H^+$ by bicarbonate produces extra $CO_2$. * **Brain RQ:** The RQ of the brain is nearly **1.0** because it primarily utilizes glucose.

Q: Which of the following will decrease the physiologic dead space?

Neck flexion. **Explanation:** **Physiologic dead space** is the sum of anatomical dead space (volume of the conducting airways) and alveolar dead space (alveoli that are ventilated but not perfused). To decrease physiologic dead space, one must either reduce the volume of the conducting airways or improve the ventilation-perfusion (V/Q) match. 1. **Why Neck Flexion is Correct:** Anatomical dead space is determined by the volume of the extra-thoracic and intra-thoracic airways. **Neck flexion** physically shortens the upper airway and reduces its internal volume. Conversely, neck extension or protruding the jaw increases dead space. This is a high-yield mechanical factor in respiratory physiology. 2. **Why the Other Options are Incorrect:** * **Emphysema:** This condition leads to the destruction of alveolar walls and capillary beds. This creates large air spaces that are ventilated but poorly perfused, significantly **increasing alveolar dead space**. * **Increase in Tidal Volume:** While increasing tidal volume improves alveolar ventilation, it also causes "traction" on the airways. High lung volumes lead to bronchodilation and expansion of the conducting zones, which **increases anatomical dead space**. * **IPPV:** Positive pressure ventilation expands the airways and can over-distend alveoli (increasing V/Q mismatch), both of which **increase dead space**. **Clinical Pearls for NEET-PG:** * **Fowler’s Method** measures anatomical dead space (using Nitrogen washout). * **Bohr’s Equation** measures physiologic dead space (using $CO_2$ levels). * In healthy individuals, physiologic dead space roughly equals anatomical dead space. * **Drugs:** Bronchodilators (like Atropine) increase dead space, while bronchoconstrictors decrease it. * **Positioning:** Supine position decreases dead space compared to an upright position.

Q: Restrictive lung diseases typically show which of the following patterns?

All of the above. **Explanation:** Restrictive lung diseases (e.g., Idiopathic Pulmonary Fibrosis, Sarcoidosis, or Chest wall deformities) are characterized by **reduced lung compliance** and a decreased ability of the lungs to expand. This leads to a global reduction in all lung volumes and capacities. 1. **Decreased Total Lung Capacity (TLC):** This is the **hallmark** of restrictive lung disease. Because the lungs are "stiff" or the chest wall is restricted, the maximum volume of air the lungs can hold is significantly reduced. 2. **Decreased Residual Volume (RV):** Unlike obstructive diseases (where air is trapped), restrictive diseases involve a collapse or scarring of parenchyma, leading to a decrease in the air remaining in the lungs after maximal expiration. 3. **Decreased Vital Capacity (VC):** Since VC is the difference between TLC and RV, and both are reduced, the total amount of air that can be exhaled after a maximal inspiration is also diminished. **Why "All of the above" is correct:** In restrictive patterns, the entire "lung volume box" shrinks. Therefore, TLC, RV, VC, and FRC (Functional Residual Capacity) all decrease proportionally. **High-Yield Clinical Pearls for NEET-PG:** * **FEV1/FVC Ratio:** In restrictive disease, the FEV1/FVC ratio is **normal or increased** (typically >0.7), because while both values decrease, the FVC decreases more significantly than the FEV1. * **Flow-Volume Loop:** Shows a characteristic **"Witch’s Hat"** appearance (narrow, tall, and shifted to the right). * **Compliance:** Lung compliance is **decreased**, meaning higher pressure is required to achieve the same change in volume.

Q: What is the effect of carbon monoxide on the oxygen-hemoglobin dissociation curve?

Shift to the left. **Explanation:** Carbon monoxide (CO) has a dual effect on hemoglobin (Hb) that severely impairs oxygen delivery to tissues. 1. **Increased Affinity:** CO has an affinity for hemoglobin approximately **210–250 times greater** than that of oxygen. When CO binds to one of the four heme sites (forming carboxyhemoglobin), it induces a conformational change in the Hb molecule. This change increases the affinity of the remaining heme sites for oxygen. 2. **The Left Shift:** Because the remaining oxygen is bound more tightly, it is not released easily at the tissue level. On the oxygen-hemoglobin dissociation curve, an increased affinity is represented by a **Shift to the Left**. This results in tissue hypoxia even if the arterial $PO_2$ remains normal. **Analysis of Incorrect Options:** * **Option A (Shift to the Right):** A right shift indicates decreased affinity (easier unloading), caused by factors like increased $H^+$ (Bohr effect), $CO_2$, temperature, or 2,3-BPG. CO does the opposite. * **Option C (No change):** CO significantly alters Hb kinetics; it never leaves the curve unchanged. * **Option D (Linear curve):** The curve remains sigmoidal but becomes "flattened" at the top because the total oxygen-carrying capacity is reduced (as CO occupies binding sites). **High-Yield Clinical Pearls for NEET-PG:** * **Haldane Effect vs. Bohr Effect:** CO poisoning does not affect the dissolved $PO_2$ in blood; therefore, arterial blood gas (ABG) may show a **normal $PaO_2$**, which can be clinically misleading. * **Cherry Red Skin:** A classic (though often late) sign of CO poisoning due to the color of carboxyhemoglobin. * **Treatment:** 100% Oxygen (to displace CO) or Hyperbaric Oxygen therapy in severe cases.

Question 1

Which of the following pulmonary function changes is NOT typically seen in emphysema?

Accepted Answer

Forced Expiratory Volume in 1 second (FEV1)

Answer

Total Lung Capacity (TLC)

Answer

Residual Volume (RV)

Answer

Diffusing capacity of the lung for carbon monoxide (DLCO)

Question 2

Which factor most affects the oxygen-carrying capacity of blood?

Accepted Answer

Hemoglobin

Answer

pH

Answer

pCO2

Answer

Red blood cell count

Question 3

Which of the following functions is associated with bronchial circulation?

Accepted Answer

Air conditioning of inhaled air

Answer

Drug absorption

Answer

Gaseous exchange

Answer

Reserve volume

Question 4

Which of the following factors does NOT affect the affinity of hemoglobin for oxygen?

Accepted Answer

PCO2

Answer

pH

Answer

Temperature

Answer

2,3-DPG

Question 5

Which of the following does not cause hyperventilation?

Accepted Answer

Pulmonary hypertension

Answer

Anxiety

Answer

High altitude

Answer

Psychotic illness

Question 6

What is the respiratory quotient on a mixed diet?

Accepted Answer

0.85

Answer

0.1

Answer

0.33

Answer

0.91

Question 7

Which of the following will decrease the physiologic dead space?

Accepted Answer

Neck flexion

Answer

Emphysema

Answer

Increase in tidal volume

Answer

Intermittent positive pressure ventilation (IPPV)

Question 8

Restrictive lung diseases typically show which of the following patterns?

Accepted Answer

All of the above

Answer

Decreased total lung capacity (TLC)

Answer

Decreased residual volume (RV)

Answer

Decreased vital capacity (VC)

Question 9

What is the effect of carbon monoxide on the oxygen-hemoglobin dissociation curve?

Accepted Answer

Shift to the left

Answer

Shift to the right

Answer

No change

Answer

Linear curve

Question 10

A 2-day-old infant born at 32 weeks' gestation has had breathing difficulties since birth and is currently on a respirator and 100% oxygen. These difficulties occur because of which one of the following?

Accepted Answer

An inability of the lung to expand when taking in air

Answer

An inability of the lung to contract to exhale

Answer

An inability of the lung to respond to insulin

Answer

An inability of the lung to respond to glucagon

Respiratory System — MCQs

Respiratory System — MCQs

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