Respiratory System Practice Questions

Q: Surfactant is primarily composed of which substance?

Phospholipids. **Explanation:** **Pulmonary surfactant** is a surface-active lipoprotein complex secreted by **Type II pneumocytes**. Its primary function is to reduce surface tension at the air-liquid interface of the alveoli, preventing alveolar collapse (atelectasis) during expiration and increasing lung compliance. **Why Phospholipids are the correct answer:** Approximately **90% of surfactant is composed of lipids**, with the remaining 10% being proteins (Surfactant proteins A, B, C, and D). Among the lipids, **phospholipids** are the predominant component. The most abundant and physiologically active phospholipid is **Dipalmitoylphosphatidylcholine (DPPC)**, also known as **Lecithin**. It is the amphipathic nature of these phospholipids that allows them to reduce surface tension effectively. **Why other options are incorrect:** * **Fibrin and Fibrinogen (A & D):** These are proteins involved in the blood coagulation cascade. While fibrin can be found in the alveoli in pathological states like ARDS (forming hyaline membranes), they are not components of normal surfactant. * **Mucoprotein (B):** These are major components of respiratory mucus secreted by goblet cells and submucosal glands, not surfactant. **High-Yield Clinical Pearls for NEET-PG:** * **L/S Ratio:** The Lecithin-to-Sphingomyelin ratio in amniotic fluid is used to assess fetal lung maturity. A ratio **>2:1** indicates mature lungs. * **NRDS:** Deficiency of surfactant in premature infants leads to **Neonatal Respiratory Distress Syndrome** (Hyaline Membrane Disease). * **Synthesis:** Surfactant synthesis begins around 24–28 weeks of gestation, but adequate levels are usually reached only after **35 weeks**. * **Glucocorticoids:** These are administered to mothers in preterm labor to accelerate surfactant production in the fetus.

Q: Over-inflation of the lung is prevented by?

Hering-Breuer reflex. **Explanation:** The **Hering-Breuer Inflation Reflex** is a protective mechanism designed to prevent over-distension of the lungs. 1. **Mechanism (Why B is correct):** When the lungs are inflated (tidal volume > 1.5 liters in adults), **stretch receptors** located in the smooth muscle of the bronchi and bronchioles are activated. These receptors send inhibitory impulses via the **Vagus nerve (CN X)** to the respiratory centers in the medulla (specifically the dorsal respiratory group). This inhibits further inspiration and initiates expiration, effectively "switching off" the inspiratory ramp. 2. **Why other options are incorrect:** * **A. Chemo-receptors:** These monitor chemical changes ($PaO_2$, $PaCO_2$, and $pH$) in the blood to regulate the rate and depth of breathing, rather than physical lung volume. * **C. Surfactant:** Produced by Type II pneumocytes, surfactant reduces surface tension to prevent alveolar collapse (atelectasis) during expiration; it does not limit inflation. * **D. Clara cells:** Now known as **Club cells**, these are non-ciliated secretory cells in the bronchioles that protect the bronchiolar epithelium and produce components of surfactant; they have no regulatory role in the inflation reflex. **High-Yield Clinical Pearls for NEET-PG:** * **Vagus Nerve:** It is the afferent limb of the Hering-Breuer reflex. Bilateral vagotomy results in deep, slow breathing. * **Threshold:** In humans, this reflex is typically inactive during quiet resting breathing and only triggers when tidal volume exceeds **~1.5 Liters** (e.g., during heavy exercise). * **Hering-Breuer Deflation Reflex:** A separate reflex that stimulates inspiration when lungs are abnormally deflated (e.g., pneumothorax).

Q: Spirometry measures all of the following, except:

None of the above. **Explanation:** The correct answer is **None of the above** because all the parameters listed (Tidal Volume, Vital Capacity, and FEV1) can be directly measured using a standard spirometer. **Understanding the Concept:** Spirometry is a pulmonary function test that measures the **volume** of air an individual can inhale or exhale as a function of **time**. * **Tidal Volume (TV):** The volume of air inspired or expired during a normal breath. * **Vital Capacity (VC):** The maximum volume of air that can be exhaled after a maximum inspiration. * **FEV1 (Forced Expiratory Volume in 1 second):** The volume of air exhaled during the first second of a forced expiratory maneuver. **Why the other options are incorrect:** Options A, B, and C are all measurable by spirometry. Therefore, they cannot be the answer to an "except" question. **High-Yield Clinical Pearls for NEET-PG:** * **The "Rule of Residual":** Spirometry **cannot** measure any lung volume that includes the **Residual Volume (RV)**. This is because RV is the air that remains in the lungs even after maximal expiration and cannot be exhaled into the machine. * **What Spirometry CANNOT measure:** 1. Residual Volume (RV) 2. Functional Residual Capacity (FRC) 3. Total Lung Capacity (TLC) * **How to measure RV/FRC/TLC:** These require specialized techniques such as **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** (the gold standard). * **FEV1/FVC Ratio:** This is the most important parameter for differentiating between Obstructive (ratio decreased) and Restrictive (ratio normal or increased) lung diseases.

Q: What is the effect on spirometry following lobectomy for bronchogenic carcinoma?

Increased dead space ventilation. **Explanation:** The correct answer is **C. Increased dead space ventilation.** **Mechanism:** Following a lobectomy, a portion of the functional lung tissue (alveoli) is removed. However, the large conducting airways (trachea and main bronchi) remain intact. Because the total lung volume decreases while the volume of the conducting zones remains relatively constant, the ratio of **dead space to tidal volume ($V_D/V_T$) increases**. Furthermore, the remaining lung tissue often undergoes compensatory hyperinflation to fill the thoracic cavity; this expansion increases the diameter of the remaining airways, further increasing the anatomical dead space. **Analysis of Incorrect Options:** * **A. Increased residual volume:** After surgical resection of lung tissue, the total lung capacity and all its sub-components, including Residual Volume (RV), typically **decrease** due to the loss of lung parenchyma. * **B. Increased vital capacity:** Vital Capacity (VC) is the maximum volume of air exhaled after a maximum inspiration. Removing a lobe directly reduces the number of functioning alveoli, leading to a **decreased** VC (a restrictive pattern). * **D. Increased closing volume:** Closing volume is the volume at which small airways in the dependent parts of the lung begin to close. While it can be affected by age and smoking, it does not characteristically increase as a direct physiological result of lobectomy itself. **High-Yield Clinical Pearls for NEET-PG:** * **Dead Space Calculation:** Remember Bohr’s equation: $V_D = V_T \times [(PaCO_2 - PeCO_2) / PaCO_2]$. * **Post-Op Spirometry:** Lobectomy results in a **Restrictive pattern** (decreased FVC, decreased FEV1, but a normal or increased FEV1/FVC ratio). * **Compensatory Changes:** The remaining lobes undergo "compensatory emphysema" (hyperinflation), which is a physiological adaptation, not a pathological one.

Q: Which lung volume or capacity can be measured by Hutchison's spirometer?

Expiratory reserve volume. **Explanation:** The core principle of spirometry (including the classic **Hutchison’s spirometer**) is that it can only measure volumes of air that can be **actively moved into or out of the lungs**. 1. **Why Expiratory Reserve Volume (ERV) is correct:** ERV is the maximum volume of air that can be exhaled after a normal tidal expiration. Since this air is physically displaced from the lungs into the spirometer, it can be directly measured. Other volumes measurable by spirometry include Tidal Volume (TV), Inspiratory Reserve Volume (IRV), and Vital Capacity (VC). 2. **Why the other options are incorrect:** * **Residual Volume (RV):** This is the air remaining in the lungs after a maximal forced expiration. Because it never leaves the lungs, a spirometer cannot "see" or measure it. * **Functional Residual Capacity (FRC) & Total Lung Capacity (TLC):** Both of these capacities include the Residual Volume (FRC = ERV + RV; TLC = VC + RV). Since RV cannot be measured by spirometry, any capacity containing it also cannot be measured. **High-Yield Clinical Pearls for NEET-PG:** * **Measurement of RV, FRC, and TLC:** These require indirect methods such as **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** (the gold standard). * **Hutchison’s Spirometer:** Invented by John Hutchison, it is a "water-seal" spirometer. It cannot measure flow rates (like FEV1) accurately; for those, a computerized pneumotachometer is used. * **Formula to remember:** Vital Capacity (VC) = TV + IRV + ERV. This is the largest volume measurable by a spirometer.

Q: What is the resting rate of O2 delivery to tissues?

250 ml/min. **Explanation:** The resting rate of oxygen delivery to tissues, also known as **Oxygen Consumption ($\dot{V}O_2$)**, refers to the amount of oxygen the body extracts and utilizes from the blood per minute under basal conditions. **Why Option B is Correct:** In a healthy adult at rest, the average oxygen consumption is approximately **250 ml/min**. This is calculated using the Fick Principle: *$\dot{V}O_2 = \text{Cardiac Output} \times (\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content})$.* With a cardiac output of 5 L/min, arterial $O_2$ at 200 ml/L, and venous $O_2$ at 150 ml/L, the consumption is: $5 \times (200 - 150) = 250 \text{ ml/min}$. **Analysis of Incorrect Options:** * **Option A (150 ml/min):** This is too low for a standard adult; it might be seen in states of extreme hypometabolism or in much smaller pediatric patients. * **Option C (300 ml/min) & D (350 ml/min):** These values represent elevated metabolic states. Oxygen consumption increases significantly during exercise, fever, or hyperthyroidism, but does not represent the "resting" rate. **High-Yield Clinical Pearls for NEET-PG:** * **Total Oxygen Delivery ($DO_2$):** Do not confuse $VO_2$ (consumption) with $DO_2$ (delivery). Total $DO_2$ is ~1000 ml/min (Cardiac Output $\times$ Arterial $O_2$ content). * **Utilization Coefficient:** At rest, tissues extract about 25% of delivered oxygen ($250/1000$). During strenuous exercise, this can increase to 75-85%. * **Respiratory Quotient (RQ):** While $O_2$ consumption is 250 ml/min, $CO_2$ production is ~200 ml/min, giving a resting RQ of 0.8 ($200/250$).

Question 1

A 38-year-old man's snoring becomes louder soon after falling asleep, interrupted by a long silent period of no breathing (apnea). He was diagnosed with Obstructive Sleep Apnea (OSA). Individuals with OSA awaken when aerial hypoxemia and hypercapnia stimulate both peripheral and central chemoreceptors. The activity of the central chemoreceptors is stimulated by which of the following?

Accepted Answer

An increase in the partial pressure of carbon dioxide (PCO2) of blood flowing through the brain

Answer

A decrease in the partial pressure of oxygen (PO2) of blood flowing through the brain

Answer

An increase in the pH of the cerebrospinal fluid (CSF)

Answer

Hypoxemia, Hypercapnia, and Metabolic acidosis

Question 2

Surfactant is primarily composed of which substance?

Accepted Answer

Phospholipids

Answer

Fibrin

Answer

Mucoprotein

Answer

Fibrinogen

Question 3

Over-inflation of the lung is prevented by?

Accepted Answer

Hering-Breuer reflex

Answer

Chemo-receptor

Answer

Surfactant

Answer

Clara cells

Question 4

Spirometry measures all of the following, except:

Accepted Answer

None of the above

Answer

Tidal volume

Answer

Vital capacity

Answer

FEV1

Question 5

What is the effect on spirometry following lobectomy for bronchogenic carcinoma?

Accepted Answer

Increased dead space ventilation

Answer

Increased residual volume

Answer

Increased vital capacity

Answer

Increased closing volume

Question 6

Oxygen content of the arterial blood is reduced in all except:

Accepted Answer

Methemoglobinemia

Answer

Fallot's tetralogy

Answer

Carbon monoxide poisoning

Answer

Fibrosing alveolitis

Question 7

What is the tidal volume?

Accepted Answer

The amount of air that normally moves into or out of the lung with each respiration.

Answer

The amount of air that enters the lung but does not participate in gas exchange.

Answer

The largest amount of air expired after maximal expiratory effort.

Answer

The largest amount of gas that can be moved into and out of the lungs in 1 minute.

Question 8

Which lung volume or capacity can be measured by Hutchison's spirometer?

Accepted Answer

Expiratory reserve volume

Answer

Residual volume

Answer

Functional residual capacity

Answer

Total lung capacity

Question 9

Administration of pure oxygen to hypoxic patients is dangerous because?

Accepted Answer

Apnea occurs due to hypostimulation of peripheral chemoreceptors.

Answer

Pulmonary edema.

Answer

Increased 2,3-Diphosphoglycerate (DPG) levels.

Answer

Convulsions.

Question 10

What is the resting rate of O2 delivery to tissues?

Accepted Answer

250 ml/min

Answer

150 ml/min

Answer

300 ml/min

Answer

350 ml/min

Respiratory System — MCQs

Respiratory System — MCQs

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