Respiratory System Practice Questions

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.

Q: What is the volume of air taken into the lungs during normal respiration called?

Tidal volume. **Explanation:** **Tidal Volume (TV)** is defined as the volume of air inspired or expired during a single cycle of normal, quiet respiration. In a healthy adult male, the average value is approximately **500 mL**. It represents the baseline ventilation required to maintain gas exchange under resting conditions. **Analysis of Incorrect Options:** * **Vital Capacity (VC):** This is the maximum volume of air a person can expel from the lungs after a maximum inhalation (VC = TV + IRV + ERV). It measures the total functional capacity of the lungs, not normal breathing. * **Timed Vital Capacity (FEV1):** This refers to the volume of air expired during the first second of a forced expiratory maneuver. It is a dynamic lung function test used clinically to differentiate between obstructive and restrictive lung diseases. * **Inspiratory Reserve Volume (IRV):** This is the additional volume of air that can be inspired over and above the normal tidal volume (approx. 2500–3000 mL). It represents the "reserve" used during deep breathing or exercise. **High-Yield Clinical Pearls for NEET-PG:** * **Anatomic Dead Space:** Out of the 500 mL of Tidal Volume, only about **350 mL** reaches the alveoli for gas exchange; the remaining **150 mL** remains in the conducting airways (Anatomic Dead Space). * **Minute Ventilation:** Calculated as $TV \times \text{Respiratory Rate}$ (approx. $500 \times 12 = 6000\text{ mL/min}$). * **Alveolar Ventilation:** A more accurate measure of gas exchange, calculated as $(TV - \text{Dead Space}) \times \text{Respiratory Rate}$. * In restrictive lung diseases (like pulmonary fibrosis), TV may remain normal or decrease, whereas in obstructive diseases (like asthma), the focus is usually on the reduction of FEV1.

Q: Which hormone accelerates surfactant production?

Glucocorticoids. **Explanation:** **Surfactant** is a surface-active lipoprotein complex (primarily Dipalmitoylphosphatidylcholine) secreted by **Type II Pneumocytes**. Its primary role is to reduce surface tension within the alveoli, preventing collapse during expiration. **Why Glucocorticoids are correct:** Glucocorticoids (Cortisol) are the most potent stimulators of surfactant synthesis. They act by accelerating the maturation of Type II pneumocytes and inducing the enzymes required for phospholipid synthesis. In clinical practice, if preterm delivery is anticipated (between 24–34 weeks), exogenous glucocorticoids like **Betamethasone or Dexamethasone** are administered to the mother to accelerate fetal lung maturity and prevent Respiratory Distress Syndrome (RDS). **Analysis of Incorrect Options:** * **Thyroxine (A):** While Thyroxine does play a minor synergistic role in lung maturation, it is not the primary hormone used clinically or physiologically for this specific acceleration compared to glucocorticoids. * **Carbamazepine (C):** This is an anticonvulsant medication used for epilepsy and trigeminal neuralgia; it has no physiological role in surfactant production. * **Iodine (D):** Iodine is essential for thyroid hormone synthesis but does not directly influence the pulmonary surfactant system. **High-Yield Clinical Pearls for NEET-PG:** * **Lecithin/Sphingomyelin (L/S) Ratio:** A ratio > 2:1 in amniotic fluid indicates fetal lung maturity. * **Inhibitors:** Insulin (maternal diabetes) and high doses of Oxygen can inhibit surfactant production or function. * **Composition:** The most abundant component is **Dipalmitoylphosphatidylcholine (DPPC)**. * **Surfactant Proteins:** SP-A and SP-D are involved in innate immunity, while SP-B and SP-C are crucial for the physical properties of the surfactant film.

Question 1

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 2

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 3

Which of the following does not cause hyperventilation?

Accepted Answer

Pulmonary hypertension

Answer

Anxiety

Answer

High altitude

Answer

Psychotic illness

Question 4

What is the respiratory quotient on a mixed diet?

Accepted Answer

0.85

Answer

0.1

Answer

0.33

Answer

0.91

Question 5

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 6

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 7

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 8

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

Question 9

What is the volume of air taken into the lungs during normal respiration called?

Accepted Answer

Tidal volume

Answer

Vital capacity

Answer

Timed vital capacity

Answer

Inspiratory reserve volume

Question 10

Which hormone accelerates surfactant production?

Accepted Answer

Glucocorticoids

Answer

Thyroxine

Answer

Carbamazepine

Answer

Iodine

Respiratory System — MCQs

Respiratory System — MCQs

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