Respiratory System Practice Questions

Q: Pulmonary surfactant is secreted by which cells?

Type II pneumocytes. **Explanation:** **Correct Answer: B. Type II pneumocytes** Pulmonary surfactant is a surface-active lipoprotein complex (primarily composed of dipalmitoylphosphatidylcholine - DPPC). It is synthesized, stored in **lamellar bodies**, and secreted by **Type II pneumocytes** (granular pneumocytes). These cells are cuboidal and cover approximately 5% of the alveolar surface area, though they outnumber Type I cells. The primary function of surfactant is to **reduce surface tension** at the air-liquid interface, preventing alveolar collapse (atelectasis) during expiration and increasing lung compliance. **Analysis of Incorrect Options:** * **Type I pneumocytes:** These are thin, squamous cells covering 95% of the alveolar surface. Their primary role is facilitating **gas exchange** due to their minimal thickness. They do not have secretory functions. * **Clara cells (Club cells):** Found in the terminal bronchioles, these cells secrete a component of surfactant (surfactant proteins A, B, and D) and help in detoxification, but they are not the primary source of pulmonary surfactant. * **Bronchial epithelial cells:** These include ciliated and goblet cells responsible for mucus production and the mucociliary escalator, not surfactant production. **High-Yield Clinical Pearls for NEET-PG:** * **Lecithin/Sphingomyelin (L/S) Ratio:** A ratio >2:1 in amniotic fluid indicates fetal lung maturity. * **Neonatal Respiratory Distress Syndrome (NRDS):** Caused by a deficiency of surfactant in premature infants (born before 34 weeks). * **Glucocorticoids:** Stimulate the maturation of Type II pneumocytes and are administered to mothers in preterm labor to prevent NRDS. * **Law of Laplace:** $P = 2T/r$. Surfactant reduces $T$ (surface tension), preventing small alveoli from emptying into larger ones.

Q: Compliance of the lung is measured by?

Elasticity. **Explanation:** **Compliance** is defined as the change in lung volume per unit change in transpulmonary pressure ($C = \Delta V / \Delta P$). In simpler terms, it represents the "distensibility" or "stretchability" of the lungs. 1. **Why Elasticity is Correct:** Compliance is the mathematical inverse of **elastic recoil** (Elasticity). While elasticity is the tendency of the lung to rebound to its original size after being stretched, compliance measures how easily the lung expands. A lung with high elastic recoil (like in pulmonary fibrosis) has low compliance, whereas a lung with low elastic recoil (like in emphysema) has high compliance. Therefore, compliance is fundamentally a measure of the lung's elastic properties. 2. **Why Other Options are Incorrect:** * **Amount of air:** While volume changes are used to calculate compliance, the "amount of air" (Static volumes) does not define the property of compliance itself. * **Blood flow:** This relates to perfusion ($Q$), which affects gas exchange but does not determine the mechanical stretchability of the lung tissue. * **Presence of fluid:** While pulmonary edema *decreases* compliance by making the lungs stiffer, compliance is not a measurement *of* fluid; it is a measurement of tissue and surface tension mechanics. **High-Yield Clinical Pearls for NEET-PG:** * **Increased Compliance:** Seen in **Emphysema** (due to loss of elastic fibers) and with **Aging**. * **Decreased Compliance:** Seen in **Pulmonary Fibrosis** (stiff lungs), **Pulmonary Edema**, and **NRDS** (lack of surfactant increases surface tension). * **Surfactant:** Increases compliance by reducing surface tension, preventing alveolar collapse. * **Total Compliance:** The combined compliance of the lung and chest wall is less than the compliance of either alone (calculated as $1/C_{total} = 1/C_{lung} + 1/C_{chest}$).

Q: What is the normal ratio of forced expiratory volume in the first second (FEV1) to the forced vital capacity (FVC) in an adult male?

80%. **Explanation:** The **FEV1/FVC ratio** (also known as the Tiffeneau-Pinelli index) is a critical parameter in spirometry used to differentiate between obstructive and restrictive lung diseases. In a healthy adult, approximately **80%** of the total air that can be forcibly exhaled (FVC) is expelled within the very first second (FEV1). **Why 80% is correct:** In healthy lungs with normal airway resistance and elastic recoil, the majority of the vital capacity is cleared rapidly. A ratio of 0.75 to 0.85 (averaging 80%) is considered the physiological norm. **Analysis of Incorrect Options:** * **95% (Option A):** This is abnormally high. While seen in some cases of severe restrictive lung disease (where FVC drops more than FEV1), it is not the standard physiological average. * **65% (Option C):** This indicates mild **obstructive** lung disease (e.g., Asthma or COPD). A ratio below 70% is the diagnostic threshold for airflow limitation. * **50% (Option D):** This represents significant airway obstruction. Such low values are typical of moderate-to-severe COPD. **High-Yield Clinical Pearls for NEET-PG:** 1. **Obstructive Disease (Asthma/COPD):** Both FEV1 and FVC decrease, but **FEV1 decreases significantly more**, leading to a **decreased ratio (<70%)**. 2. **Restrictive Disease (Fibrosis):** Both FEV1 and FVC decrease proportionately, or FVC decreases more. Consequently, the **ratio remains normal or is increased**. 3. **Flow-Volume Loops:** In obstructive disease, the loop shows a "scooped-out" appearance; in restrictive disease, the loop is tall, narrow, and shifted to the right.

Q: Which gas is used to measure the diffusing capacity of the lungs?

Carbon monoxide. **Explanation:** The diffusing capacity of the lung (DLCO) measures the ability of the lungs to transfer gas from the inhaled air to the red blood cells in the pulmonary capillaries. **Why Carbon Monoxide (CO) is the Correct Answer:** Carbon monoxide is the gas of choice because it is **diffusion-limited**. CO has an extremely high affinity for hemoglobin (approximately 210–240 times that of oxygen). When a small, non-toxic amount is inhaled, it binds almost instantaneously to hemoglobin, keeping the partial pressure of CO in the plasma near zero. This creates a stable and maximal partial pressure gradient between the alveoli and the capillary, ensuring that the rate of transfer depends solely on the properties of the alveolar-capillary membrane (thickness and surface area). **Analysis of Incorrect Options:** * **B. Carbon Dioxide (CO₂):** CO₂ diffuses 20 times faster than oxygen; its transfer is limited by perfusion (blood flow), not diffusion, making it unsuitable for measuring diffusing capacity. * **C. Nitrogen (N₂):** Nitrogen is an inert gas that does not bind to hemoglobin and reaches equilibrium rapidly, making it ineffective for measuring membrane diffusion. * **D. Helium (He):** Helium is used in pulmonary function tests to measure **Functional Residual Capacity (FRC)** and residual volume via the helium dilution method, but it does not cross the alveolar-capillary membrane. **High-Yield Clinical Pearls for NEET-PG:** * **DLCO is increased in:** Polycythemia, Alveolar hemorrhage (e.g., Goodpasture syndrome), and early stages of Congestive Heart Failure (due to increased pulmonary capillary blood volume). * **DLCO is decreased in:** Emphysema (loss of surface area), Interstitial Lung Disease/Fibrosis (increased membrane thickness), and Anemia. * **Formula:** $DLCO = \text{Rate of CO uptake} / (\text{Alveolar } P_{CO} - \text{Capillary } P_{CO})$. Since capillary $P_{CO}$ is negligible, it simplifies the calculation.

Q: A 4-year-old asthmatic child presents with respiratory distress, characterized by unresponsiveness, rapid shallow breathing, and pulsus paradoxus. Arterial blood gas analysis reveals respiratory acidosis. What is the next most appropriate step in managing this patient?

Urgent endotracheal intubation. ### Explanation The patient is presenting with **Status Asthmaticus** with "Imminent Respiratory Failure." The clinical signs of **unresponsiveness** (altered sensorium), **rapid shallow breathing** (exhaustion), and **respiratory acidosis** on ABG indicate that the patient is no longer able to maintain adequate ventilation. **1. Why Option A is Correct:** In severe asthma, respiratory acidosis (elevated $PaCO_2$) is an ominous sign. Normally, an asthmatic patient hyperventilates, leading to respiratory alkalosis. When the patient tires, $CO_2$ begins to rise. The combination of altered mental status and acidosis indicates that the respiratory muscles are failing. **Urgent endotracheal intubation** and mechanical ventilation are mandatory to secure the airway and provide ventilatory support. **2. Why Other Options are Incorrect:** * **Option B:** Hyperbaric oxygen is used for carbon monoxide poisoning or decompression sickness; it has no role in acute asthma management. * **Option C:** While MDIs are standard for mild-to-moderate asthma, they are insufficient for a patient in respiratory failure who cannot coordinate breaths or move enough air to deliver the drug to the distal airways. * **Option D:** Terbutaline and aminophylline are second-line bronchodilators. In a patient with altered sensorium and acidosis, pharmacological bronchodilation alone is too slow and risky; the immediate priority is airway protection. **Clinical Pearls for NEET-PG:** * **The "Silent Chest":** A dangerous sign in asthma where airflow is so limited that wheezing disappears. * **ABG Progression:** Early Asthma → Respiratory Alkalosis (Low $PaCO_2$). Late/Severe Asthma → Normal $PaCO_2$ (Pseudo-normalization, a warning sign). Imminent Failure → **Respiratory Acidosis** (High $PaCO_2$). * **Pulsus Paradoxus:** Defined as a drop in systolic BP >10 mmHg during inspiration; it signifies severe air trapping and increased work of breathing.

Q: A 70-year-old man presents with a 16-week history of progressive dysphagia and recurrent pneumonia episodes. He also has palpable stony hard neck nodes on examination. What is the most likely diagnosis?

Carcinoma of the esophagus. **Explanation:** The clinical presentation of **progressive dysphagia** in an elderly male (70 years), associated with **stony hard neck nodes** (suggestive of metastatic lymphadenopathy), is a classic "red flag" for malignancy. In this case, **Carcinoma of the Esophagus** is the most likely diagnosis. **Why the correct answer is right:** 1. **Progressive Dysphagia:** Malignant strictures typically cause dysphagia that starts with solids and progresses to liquids as the lumen narrows. 2. **Metastasis:** The presence of "stony hard" neck nodes (likely Virchow’s node or deep cervical nodes) strongly indicates metastatic spread, a hallmark of advanced esophageal cancer. 3. **Recurrent Pneumonia:** This occurs due to chronic aspiration of saliva/food or the development of a **tracheoesophageal fistula**, a common complication of esophageal malignancy. **Why other options are incorrect:** * **Achalasia Cardia:** Typically presents in younger patients with long-standing dysphagia (often paradoxical, for liquids more than solids) and lacks hard lymphadenopathy. * **Diffuse Esophageal Spasm:** Characterized by intermittent chest pain and "corkscrew esophagus" on imaging; it does not cause weight loss or lymphadenopathy. * **Zenker’s Diverticulum:** While it causes dysphagia and aspiration, the neck mass is typically soft, fluctuant, and may gurgle (Boyce sign), rather than being stony hard. **High-Yield Clinical Pearls for NEET-PG:** * **Squamous Cell CA:** Most common worldwide; associated with smoking and alcohol. * **Adenocarcinoma:** Most common in the West; associated with GERD and **Barrett’s Esophagus**. * **Investigation of Choice:** Upper GI Endoscopy (UGIE) with biopsy. * **Staging:** EUS (Endoscopic Ultrasound) is the most accurate for T and N staging.

Q: What is the effect of cutting the spinal cord above the medulla on respiration?

Irregular and gasping. ### Explanation **Correct Answer: D. Irregular and gasping** **Underlying Concept:** The fundamental rhythm of respiration is generated by the **Pre-Bötzinger complex** and the **Medullary Respiratory Centers** (Dorsal and Ventral Respiratory Groups). While the medulla can generate a basic rhythm, it requires input from higher centers (Pons and Cortex) and peripheral feedback to maintain a smooth, regular pattern. When the spinal cord is cut **above the medulla** (specifically at the midbrain-medullary junction or high medullary level), the connection between the **Pons** (Pneumotaxic and Apneustic centers) and the **Medulla** is severed. The isolated medulla, deprived of the "fine-tuning" influence of the pontine centers, produces a primitive, disorganized rhythm characterized by **irregular and gasping** breaths (ataxic breathing). **Why other options are incorrect:** * **A. Breathing becomes slower and deeper:** This occurs when the **Vagus nerve** is bilaterally transected (loss of Hering-Breuer reflex) or when the **Pneumotaxic center** is inhibited. * **B. Apneustic breathing:** This is characterized by prolonged inspiratory gasps. It occurs when there is a lesion in the **upper pons** (Pneumotaxic center) combined with a bilateral **Vagotomy**. * **C. Breathing ceases:** Respiration stops (Apnea) only if the lesion is **below the medulla** (at or above C3-C5), which severs the connection between the respiratory centers and the phrenic nerve (which innervates the diaphragm). **High-Yield Facts for NEET-PG:** * **Pneumotaxic Center (Upper Pons):** Acts as the "off-switch" for inspiration; limits tidal volume. * **Apneustic Center (Lower Pons):** Delays the "off-switch," prolonging inspiration. * **C3, 4, 5 keep the diaphragm alive:** A spinal cord injury at C3 or above leads to immediate respiratory arrest. * **Cheyne-Stokes Breathing:** Often seen in heart failure or cortical brain damage (uphill/downhill pattern).

Q: Laminar flow is dependent on which of the following factors?

Critical velocity. **Explanation:** The type of airflow in the respiratory tract (laminar vs. turbulent) is determined by the **Reynolds Number (Re)**. According to the formula $Re = \frac{\rho vd}{\eta}$ (where $\rho$ is density, $v$ is velocity, $d$ is diameter, and $\eta$ is viscosity), flow remains **laminar** as long as the velocity of the gas stays below a specific threshold known as the **Critical Velocity**. 1. **Why A is correct:** Critical velocity is the maximum velocity at which airflow remains laminar. Once the gas velocity exceeds this point, the Reynolds number surpasses 2000, and the flow transitions from smooth, streamlined (laminar) layers to disorganized, eddy-forming **turbulent flow**. Therefore, the maintenance of laminar flow is directly dependent on staying below this critical velocity. 2. **Why B is incorrect:** While viscosity ($\eta$) influences the Reynolds number, laminar flow itself is primarily driven by the pressure gradient and is inversely proportional to viscosity (Poiseuille’s Law). However, the *transition* and *dependency* of flow type are defined by the velocity threshold. 3. **Why C is incorrect:** Constant velocity simply means the speed does not change; it does not dictate whether the flow is laminar or turbulent. 4. **Why D is incorrect:** Critical closing pressure refers to the pressure at which small airways or blood vessels collapse (Laplace’s Law), which is unrelated to the pattern of fluid flow. **High-Yield NEET-PG Pearls:** * **Laminar Flow:** Occurs in small peripheral airways (bronchioles) where velocity is low. * **Turbulent Flow:** Occurs in large airways (trachea) where velocity is high. * **Heliox Therapy:** In airway obstruction, replacing Nitrogen with Helium (lower density) reduces the Reynolds number, converting turbulent flow back to laminar flow, thereby decreasing the work of breathing.

Question 1

Peripheral chemoreceptors are maximally stimulated by which of the following?

Accepted Answer

Cyanide

Answer

Acidosis

Answer

Hypercapnia

Answer

Carbon dioxide

Question 2

Pulmonary surfactant is secreted by which cells?

Accepted Answer

Type II pneumocytes

Answer

Type I pneumocytes

Answer

Clara cells

Answer

Bronchial epithelial cells

Question 3

Compliance of the lung is measured by?

Accepted Answer

Elasticity

Answer

Amount of air

Answer

Blood flow

Answer

Presence of fluid

Question 4

What is the normal ratio of forced expiratory volume in the first second (FEV1) to the forced vital capacity (FVC) in an adult male?

Accepted Answer

80%

Answer

95%

Answer

65%

Answer

50%

Question 5

Which gas is used to measure the diffusing capacity of the lungs?

Accepted Answer

Carbon monoxide

Answer

Carbon dioxide

Answer

Nitrogen

Answer

Helium

Question 6

The provided graph illustrates the relationship between lung volume and intrapleural pressure during inspiration and expiration. What is the most likely explanation for the observed pattern?

Accepted Answer

The difference in surfactant activity during inspiration and expiration.

Answer

The difference between active and passive work performed during respiration.

Answer

The variation in airway resistance between inspiration and expiration.

Answer

The fluctuations in intrapleural pressure.

Question 7

A 4-year-old asthmatic child presents with respiratory distress, characterized by unresponsiveness, rapid shallow breathing, and pulsus paradoxus. Arterial blood gas analysis reveals respiratory acidosis. What is the next most appropriate step in managing this patient?

Accepted Answer

Urgent endotracheal intubation

Answer

Hyperbaric oxygen therapy

Answer

Metered-dose inhaler with salbutamol and corticosteroids

Answer

Subcutaneous terbutaline with an aminophylline drip

Question 8

A 70-year-old man presents with a 16-week history of progressive dysphagia and recurrent pneumonia episodes. He also has palpable stony hard neck nodes on examination. What is the most likely diagnosis?

Accepted Answer

Carcinoma of the esophagus

Answer

Achalasia Cardia

Answer

Diffuse esophageal spasm

Answer

Zenker's diverticulum

Question 9

What is the effect of cutting the spinal cord above the medulla on respiration?

Accepted Answer

Irregular and gasping

Answer

Breathing becomes slower and deeper

Answer

Apneustic breathing

Answer

Breathing ceases

Question 10

Laminar flow is dependent on which of the following factors?

Accepted Answer

Critical velocity

Answer

Viscosity

Answer

Constant velocity

Answer

Critical closing pressure

Respiratory System — MCQs

Respiratory System — MCQs

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