Respiratory System Practice Questions

Q: The following illustration of the Spirogram showing the arrow indicates:

Vital capacity. ***Vital capacity*** - **Vital capacity** is the maximum volume of air that can be exhaled after maximum inspiration, representing the sum of **inspiratory reserve volume (IRV)**, **tidal volume (TV)**, and **expiratory reserve volume (ERV)**. - It typically measures around **4800 mL** in healthy adults and is a key indicator of **respiratory muscle strength** and **lung function**. *Tidal volume* - **Tidal volume** represents only the normal volume of air inhaled or exhaled during quiet breathing, typically around **500 mL**. - It is a much smaller component within the vital capacity and would not encompass the entire range shown by the arrow in a spirogram. *Expiratory reserve volume* - **Expiratory reserve volume** is the additional air that can be exhaled after normal expiration, typically around **1100 mL**. - It represents only one component of vital capacity and would be shown as a smaller segment below the tidal volume baseline. *Total lung capacity* - **Total lung capacity** includes the **residual volume** (air remaining in lungs after maximum expiration) which cannot be measured by spirometry. - It represents the sum of vital capacity plus **residual volume** (~1200 mL), making it larger than what can be demonstrated on a standard spirogram.

Q: Tidal volume is calculated by?

Inspiratory capacity minus the inspiratory reserve volume. **Explanation** To solve this question, one must understand the relationship between **Lung Volumes** (primary measurements) and **Lung Capacities** (sums of two or more volumes). **1. Why Option A is Correct:** Inspiratory Capacity (IC) is the maximum volume of air that can be inspired after a normal tidal expiration. It is the sum of the **Tidal Volume (TV)** and the **Inspiratory Reserve Volume (IRV)**. * **Formula:** $IC = TV + IRV$ * Therefore, **$TV = IC - IRV$**. This mathematical derivation makes Option A the correct calculation for Tidal Volume. **2. Analysis of Incorrect Options:** * **Option B:** Total Lung Capacity (TLC) minus Residual Volume (RV) equals **Vital Capacity (VC)**, not TV. ($VC = TLC - RV$) * **Option C:** Functional Residual Capacity (FRC) minus Residual Volume (RV) equals **Expiratory Reserve Volume (ERV)**. ($FRC = ERV + RV$) * **Option D:** Vital Capacity (VC) minus Expiratory Reserve Volume (ERV) equals **Inspiratory Capacity (IC)**. ($VC = IC + ERV$) **Clinical Pearls for NEET-PG:** * **Tidal Volume (TV):** Normal value is approximately **500 mL** in a healthy adult. * **Dead Space:** Out of 500 mL TV, only ~350 mL reaches the alveoli (Alveolar ventilation); ~150 mL remains in the conducting airways (Anatomical Dead Space). * **Spirometry:** Remember that **Residual Volume (RV)**, **Functional Residual Capacity (FRC)**, and **Total Lung Capacity (TLC)** cannot be measured by simple spirometry (they require helium dilution or body plethysmography). * **High-Yield Equation:** $Minute Ventilation = TV \times Respiratory Rate$.

Q: The curve indicated by the question mark is caused by which condition?

Pulmonary fibrosis. ***Pulmonary fibrosis*** - Shows a **restrictive pattern** with a small, proportionally reduced flow-volume loop where both **FVC** and **peak expiratory flow rate (PEFR)** are decreased, but the **PEFR/FVC ratio** remains normal or elevated. - The loop maintains its **normal shape** but is smaller overall due to **reduced lung compliance** and **decreased total lung capacity**. *Bronchial asthma* - Produces an **obstructive pattern** with a characteristic **scooped-out expiratory limb** due to **airway narrowing** and **bronchospasm**. - Shows **reduced peak expiratory flow** with **prolonged expiration** and potential **air trapping**, creating a concave expiratory curve. *Emphysema* - Demonstrates **severe obstructive pattern** with **markedly reduced peak flow** and a **severely scooped expiratory limb** due to **loss of elastic recoil**. - Features **significant air trapping** with **increased residual volume** and a **flattened, prolonged expiratory phase**. *Chronic bronchitis* - Shows **obstructive pattern** with **reduced expiratory flow rates** and a **scooped-out expiratory limb** due to **airway inflammation** and **mucus hypersecretion**. - Exhibits **impaired airway clearance** leading to **flow limitation** and **abnormal expiratory curve morphology**.

Q: What is the volume of air in the lungs after a normal expiration called?

Functional Residual Capacity (FRC). ### Explanation The correct answer is **Functional Residual Capacity (FRC)**. **1. Why FRC is Correct:** Functional Residual Capacity is defined as the volume of air remaining in the lungs at the end of a **normal (passive) expiration**. It represents the equilibrium point of the respiratory system where the inward elastic recoil of the lungs exactly balances the outward chest wall recoil. Mathematically, it is the sum of Expiratory Reserve Volume and Residual Volume (**FRC = ERV + RV**). **2. Why Other Options are Incorrect:** * **Expiratory Reserve Volume (ERV):** This is the maximum volume of air that can be exhaled *after* a normal tidal expiration. It is a component of FRC, not the total volume remaining. * **Residual Volume (RV):** This is the volume of air remaining in the lungs after a **maximal** forced expiration. It cannot be measured by simple spirometry. * **Tidal Capacity (TC):** This is a distractor term. The correct term is **Tidal Volume (TV)**, which is the volume of air inspired or expired during a single normal breath (approx. 500 mL). **3. NEET-PG High-Yield Pearls:** * **Measurement:** FRC cannot be measured by spirometry (because it contains RV). It is measured via **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography**. * **Clinical Significance:** FRC acts as a buffer to prevent large fluctuations in alveolar gas tensions ($PaO_2$) during the respiratory cycle. * **Positioning:** FRC **decreases** in the supine position (due to abdominal contents pushing against the diaphragm) and in obesity, pregnancy, and restrictive lung diseases. * **Closing Capacity:** If FRC falls below the "Closing Capacity," small airways collapse during normal breathing, leading to V/Q mismatch.

Q: A man has an intrapleural pressure of -5 cm H2O before inspiration and -10 cm H2O at the end of inspiration. He inspires 1200 ml. What is the compliance of the lungs?

240 ml/cm H2O. ### Explanation **1. Understanding the Correct Answer (C: 240 ml/cm H₂O)** Lung compliance ($C_L$) is defined as the change in lung volume ($\Delta V$) per unit change in transpulmonary pressure ($\Delta P$). In a static state (at the beginning and end of inspiration), the change in intrapleural pressure reflects the change in pressure required to expand the lungs. The formula is: $$Compliance (C) = \frac{\Delta V}{\Delta P}$$ * **Change in Volume ($\Delta V$):** 1200 ml * **Change in Pressure ($\Delta P$):** $(-5 \text{ cm H}_2\text{O}) - (-10 \text{ cm H}_2\text{O}) = 5 \text{ cm H}_2\text{O}$ * **Calculation:** $1200 \text{ ml} / 5 \text{ cm H}_2\text{O} = \mathbf{240 \text{ ml/cm H}_2\text{O}}$ **2. Why Other Options are Incorrect** * **A (50 ml/cm H₂O):** This value is too low for normal human lungs and would represent a highly "stiff" lung (e.g., severe fibrosis). * **B (120 ml/cm H₂O):** This would result if the pressure change was 10 cm H₂O instead of 5. * **D (250 ml/cm H₂O):** While close to the average normal value (200–250 ml/cm H₂O), it does not match the specific mathematical calculation derived from the data provided in the question. **3. Clinical Pearls & High-Yield Facts** * **Normal Value:** The average compliance of the combined human lung-chest wall system is approximately **110 ml/cm H₂O**, while the lungs alone are roughly **200 ml/cm H₂O**. * **Increased Compliance:** Seen in **Emphysema** due to the loss of elastic fibers (the lung is "easy to blow up" but has poor elastic recoil). * **Decreased Compliance:** Seen in **Pulmonary Fibrosis**, Pulmonary Edema, and Lack of Surfactant (the lung is "stiff"). * **Surfactant:** Increases compliance by reducing surface tension, preventing alveolar collapse at low volumes.

Q: Kussmaul respiration occurs in response to what condition?

Decrease in blood pH. **Explanation:** **Kussmaul respiration** is a deep, rapid, and labored breathing pattern. It is a physiological compensatory mechanism for **metabolic acidosis**, characterized by a **decrease in blood pH**. 1. **Why Option A is Correct:** When blood pH drops (acidemia), the increased concentration of hydrogen ions ($H^+$) stimulates **peripheral chemoreceptors** (carotid and aortic bodies) and **central chemoreceptors**. This triggers the respiratory center in the medulla to increase the rate and depth of ventilation. The goal is to "blow off" excess Carbon Dioxide ($CO_2$), thereby reducing volatile acid levels and attempting to return the blood pH toward its normal range (7.35–7.45). This is classically seen in **Diabetic Ketoacidosis (DKA)**. 2. **Why Other Options are Incorrect:** * **Option B:** An increase in blood pH (alkalosis) leads to hypoventilation (slow, shallow breathing) to retain $CO_2$ and lower the pH. * **Option C:** Obstructive diseases (like Asthma or COPD) typically present with wheezing, prolonged expiration, or pursed-lip breathing, rather than the rhythmic deep gasping of Kussmaul’s. * **Option D:** Carbon monoxide poisoning causes tissue hypoxia but often does not stimulate chemoreceptors initially because $PaO_2$ remains normal; it does not typically present with Kussmaul breathing unless severe lactic acidosis develops. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Kussmaul Causes (KUSSMAUL):** **K**etones (DKA), **U**remia (Renal failure), **S**epsis, **S**alicylates, **M**ethanol, **A**ldehydes, **U**ndetermined (Lactic) **L**actic acidosis. * **Distinction:** Do not confuse Kussmaul **respiration** (breathing) with Kussmaul **sign** (paradoxical rise in JVP on inspiration, seen in constrictive pericarditis). * **Key Feature:** Unlike Cheyne-Stokes breathing, Kussmaul respiration is **constant and rhythmic** without periods of apnea.

Q: What is an important non-respiratory function of the lungs?

Defense against inhaled air. **Explanation:** The lungs are not only responsible for gas exchange but also serve as a vital immunological barrier. **Defense against inhaled air** is a primary non-respiratory function because the respiratory tract is constantly exposed to pathogens, dust, and pollutants. This defense is mediated by: 1. **Mucociliary Escalator:** Ciliated epithelium moves mucus-trapped particles upward toward the pharynx. 2. **Alveolar Macrophages (Dust Cells):** These phagocytose small particles that reach the alveoli. 3. **Secretory IgA and Lysozymes:** Present in the airway surface liquid to neutralize pathogens. **Analysis of Incorrect Options:** * **A. Anion balance:** While the lungs regulate acid-base balance by exhaling $CO_2$ (volatile acid), they do not directly regulate specific anion concentrations (like chloride or phosphate); this is primarily a renal function. * **C & D. Potassium and Calcium balance:** These are strictly regulated by the kidneys and endocrine system (e.g., Aldosterone for $K^+$, Parathyroid hormone for $Ca^{2+}$). The lungs have no physiological role in the homeostasis of these electrolytes. **High-Yield NEET-PG Pearls:** * **Metabolic Functions:** The lungs are the primary site for the conversion of **Angiotensin I to Angiotensin II** via Angiotensin-Converting Enzyme (ACE) located in the pulmonary capillary endothelium. * **Inactivation:** The lungs inactivate Bradykinin, Serotonin, and Prostaglandins ($E_1, E_2, F_{2\alpha}$), but notably **do not** inactivate Epinephrine or Histamine. * **Surfactant:** Produced by Type II Pneumocytes, it prevents alveolar collapse and also plays a role in innate immunity (SP-A and SP-D).

Q: The afferent (sensory) endings for the Hering-Breuer reflex are mechanoreceptors located in which part of the respiratory system?

Bronchi and bronchioles. **Explanation** The **Hering-Breuer Inflation Reflex** is a protective mechanism that prevents over-inflation of the lungs. The reflex is initiated when the tidal volume exceeds a certain threshold (typically >1.5 liters in adults). **1. Why Bronchi and Bronchioles are correct:** The afferent receptors for this reflex are **slowly adapting stretch receptors (mechanoreceptors)** located within the smooth muscle walls of the **bronchi and bronchioles**. When the lungs inflate, these receptors are stretched, sending inhibitory impulses via the **Vagus nerve (CN X)** to the inspiratory center (dorsal respiratory group) in the medulla. This terminates inspiration and initiates expiration, effectively regulating the depth of breathing. **2. Why other options are incorrect:** * **Carotid arteries:** These contain peripheral chemoreceptors (Carotid bodies) that sense changes in $PaO_2$, $PaCO_2$, and pH, not lung stretch. * **Alveoli:** While gas exchange occurs here, the primary stretch receptors for the Hering-Breuer reflex are located in the conducting airways (bronchi/bronchioles), not the alveolar walls. (Note: J-receptors are located near alveolar capillaries but respond to congestion/edema). * **Diaphragm:** This is an effector muscle. It contains muscle spindles, but they are not the primary mediators of the Hering-Breuer reflex. **High-Yield Clinical Pearls for NEET-PG:** * **Afferent Pathway:** Vagus Nerve (CN X). * **Effect:** It increases the respiratory rate by shortening the duration of inspiration (it is a "self-terminating" mechanism). * **Infants:** This reflex is much more active and physiologically significant in neonates than in healthy adults. * **Hering-Breuer Deflation Reflex:** A separate reflex where lung deflation triggers an increase in inspiratory effort (to prevent lung collapse).

Question 1

The following illustration of the Spirogram showing the arrow indicates:

Accepted Answer

Vital capacity

Answer

Tidal volume

Answer

Expiratory reserve volume

Answer

Total lung capacity

Question 2

Which is responsible for respiratory drive?

Accepted Answer

CO2

Answer

O2

Answer

CO

Answer

Bicarbonate ions

Question 3

Tidal volume is calculated by?

Accepted Answer

Inspiratory capacity minus the inspiratory reserve volume

Answer

Total lung capacity minus the residual volume

Answer

Functional residual capacity minus residual volume

Answer

Vital capacity minus expiratory reserve volume

Question 4

The curve indicated by the question mark is caused by which condition?

Accepted Answer

Pulmonary fibrosis

Answer

Bronchial asthma

Answer

Emphysema

Answer

Chronic bronchitis

Question 5

What is the volume of air in the lungs after a normal expiration called?

Accepted Answer

Functional Residual Capacity (FRC)

Answer

Expiratory Reserve Volume (ERV)

Answer

Residual Volume (RV)

Answer

Tidal Capacity (TC)

Question 6

A man has an intrapleural pressure of -5 cm H2O before inspiration and -10 cm H2O at the end of inspiration. He inspires 1200 ml. What is the compliance of the lungs?

Accepted Answer

240 ml/cm H2O

Answer

50 ml/cm H2O

Answer

120 ml/cm H2O

Answer

250 ml/cm H2O

Question 7

Kussmaul respiration occurs in response to what condition?

Accepted Answer

Decrease in blood pH

Answer

Increase in blood pH

Answer

Obstructive pulmonary disease

Answer

Carbon monoxide poisoning

Question 8

What is an important non-respiratory function of the lungs?

Accepted Answer

Defense against inhaled air

Answer

Anion balance

Answer

Potassium balance

Answer

Calcium balance

Question 9

Which of the following conditions is NOT associated with a decrease in pO2?

Accepted Answer

Interstitial fibrosing alveolitis

Answer

COPD

Answer

CHF

Answer

Bronchiectasis

Question 10

The afferent (sensory) endings for the Hering-Breuer reflex are mechanoreceptors located in which part of the respiratory system?

Accepted Answer

Bronchi and bronchioles

Answer

Carotid arteries

Answer

Alveoli

Answer

Diaphragm

Respiratory System — MCQs

Respiratory System — MCQs

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