Respiratory System Practice Questions

Q: Arterial PO2 is decreased in hypoxia due to which of the following conditions?

COPD (Chronic Obstructive Pulmonary Disease). **Explanation:** The core concept in this question is differentiating between the types of hypoxia based on **Arterial Oxygen Tension ($PaO_2$)**. **1. Why COPD is Correct:** COPD causes **Hypoxic Hypoxia**. In COPD, structural damage to the alveoli (emphysema) and airway obstruction (bronchitis) lead to ventilation-perfusion ($V/Q$) mismatch and impaired gas exchange. This results in a failure to oxygenate the blood in the lungs, leading to a **decreased $PaO_2$**. **2. Why the other options are incorrect:** * **Cyanide Poisoning (Histotoxic Hypoxia):** The $PaO_2$ and oxygen content are normal. Hypoxia occurs because cyanide inhibits *cytochrome oxidase* in the mitochondria, preventing tissues from utilizing the oxygen delivered to them. * **Carbon Monoxide Poisoning (Anemic Hypoxia):** CO binds to hemoglobin with high affinity, reducing oxygen-carrying capacity. However, since $PaO_2$ represents oxygen dissolved in plasma (not bound to Hb), the **$PaO_2$ remains normal**. * **Shock (Stagnant Hypoxia):** In shock, the $PaO_2$ is typically normal initially. Hypoxia occurs because of reduced cardiac output and slow blood flow, leading to inadequate delivery of oxygen to tissues despite normal arterial oxygenation. **High-Yield NEET-PG Pearls:** * **Hypoxic Hypoxia** (e.g., High altitude, COPD, Hypoventilation) is the **only** type where $PaO_2$ is decreased. * In **Anemic Hypoxia**, $PaO_2$ is normal, but total oxygen content ($CaO_2$) is decreased. * **Pulse Oximetry ($SpO_2$)** is falsely normal or high in CO poisoning because the sensor cannot distinguish between carboxyhemoglobin and oxyhemoglobin. * **A-a Gradient:** Useful for narrowing down causes of decreased $PaO_2$; it is normal in hypoventilation/high altitude but increased in COPD/V-Q mismatch.

Q: The functional residual capacity is best defined as the sum of which two lung volumes?

Residual Volume and Expiratory Reserve Volume. **Explanation** **Functional Residual Capacity (FRC)** is the volume of air remaining in the lungs at the end of a normal, quiet expiration (at the end of a tidal breath). It represents the equilibrium point where the inward elastic recoil of the lungs exactly balances the outward chest wall expansion. 1. **Why Option B is Correct:** FRC is the sum of **Expiratory Reserve Volume (ERV)** and **Residual Volume (RV)**. * **ERV:** The additional volume that can be exhaled forcefully after a normal tidal expiration. * **RV:** The volume remaining in the lungs after maximal forced expiration (which cannot be measured by simple spirometry). Mathematically: **FRC = ERV + RV**. 2. **Analysis of Incorrect Options:** * **Option A:** Tidal Volume (TV) + Inspiratory Reserve Volume (IRV) = **Inspiratory Capacity (IC)**. * **Option C:** This combination does not represent a standard physiological capacity. * **Option D:** TV + IRV + ERV = **Vital Capacity (VC)**. This is the maximum volume of air a person can expel from the lungs after a maximum inhalation. **High-Yield Clinical Pearls for NEET-PG:** * **Measurement:** FRC cannot be measured by simple spirometry because it contains Residual Volume. It is measured via **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** (the gold standard). * **Clinical Significance:** FRC acts as a "buffer" for gas exchange, preventing large fluctuations in O₂ and CO₂ levels during the breathing cycle. * **Pathology:** FRC is **increased** in obstructive diseases (e.g., Emphysema due to air trapping) and **decreased** in restrictive diseases (e.g., Pulmonary Fibrosis) and conditions like obesity or pregnancy.

Q: Dead space is increased by all, except:

Endotracheal intubation. **Explanation:** **Anatomical dead space** refers to the volume of the conducting airways (from the nose/mouth down to the terminal bronchioles) where no gas exchange occurs. The correct answer is **Endotracheal intubation** because it **decreases** anatomical dead space. 1. **Why Endotracheal Intubation is correct:** An endotracheal tube bypasses the upper respiratory tract (nose, pharynx, and larynx), which accounts for a significant portion of the anatomical dead space. By providing a direct, shorter route to the trachea, the total volume of non-perfused conducting zone is reduced. (Note: Tracheostomy also decreases dead space for the same reason). 2. **Why the other options are incorrect:** * **Anticholinergic drugs (e.g., Atropine):** These drugs cause bronchodilation. By increasing the diameter of the conducting airways, the internal volume (dead space) increases. * **Standing:** Due to gravity, there is increased ventilation-perfusion (V/Q) mismatch at the apices of the lungs. Alveoli at the apex are ventilated but poorly perfused, increasing **physiological dead space**. * **Hyperextension of neck:** This physical maneuver stretches and widens the caliber of the upper airway, thereby increasing the anatomical dead space volume. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Dead Space:** Approximately **2 ml/kg** or 150 ml in a healthy adult. * **Fowler’s Method:** Used to measure **Anatomical** dead space (using Nitrogen washout). * **Bohr’s Equation:** Used to measure **Physiological** dead space (using $CO_2$ levels). * **Physiological Dead Space = Anatomical + Alveolar Dead Space.** In healthy individuals, physiological and anatomical dead space are nearly equal.

Q: Which spirometry feature is characteristic of asthma?

FEV1/FEV ratio shows a downward trend. **Explanation:** Asthma is a classic example of an **obstructive lung disease** characterized by reversible airway narrowing. The hallmark of any obstructive pathology is an increased resistance to airflow, which is most pronounced during expiration. **Why Option B is Correct:** In obstructive diseases like asthma, the **FEV1** (Forced Expiratory Volume in 1 second) decreases significantly more than the **FVC** (Forced Vital Capacity). Because the numerator (FEV1) drops more drastically than the denominator (FVC), the **FEV1/FVC ratio decreases** (typically <70%). This downward trend is the most sensitive spirometric indicator of airway obstruction. **Analysis of Incorrect Options:** * **Option A:** FEV1 (or FEV) shows a **downward** trend during an asthma attack due to bronchoconstriction and mucus plugging. * **Option C:** **PEF (Peak Expiratory Flow)** measures the maximum speed of expiration. In asthma, PEF shows a **downward** trend. Monitoring PEF variability is a key tool for assessing asthma severity and control. * **Option D:** **RV (Residual Volume)** actually shows an **upward** trend in asthma. This occurs due to "air trapping," where narrowed airways close prematurely during expiration, leaving more air behind in the lungs. **High-Yield Clinical Pearls for NEET-PG:** * **Reversibility Criteria:** A definitive diagnosis of asthma via spirometry requires an improvement in FEV1 of **>12% and >200 mL** after inhalation of a short-acting beta-agonist (e.g., Salbutamol). * **Flow-Volume Loop:** In asthma, the expiratory limb of the loop typically shows a **"scooped-out"** appearance. * **DLCO:** Unlike Emphysema (where DLCO is decreased), DLCO in Asthma is usually **normal or slightly increased**.

Q: Conversion of angiotensin-I to angiotensin-II occurs in which organ?

Lung. **Explanation:** The conversion of Angiotensin-I to Angiotensin-II is a critical step in the **Renin-Angiotensin-Aldosterone System (RAAS)**. This reaction is catalyzed by the **Angiotensin-Converting Enzyme (ACE)**. 1. **Why Lungs are correct:** While ACE is present in various vascular beds, its highest concentration is found on the **luminal surface of the vascular endothelial cells of the lungs**. As the entire cardiac output passes through the pulmonary circulation, the lungs serve as the primary site for this conversion. 2. **Why other options are incorrect:** * **Kidney:** The kidneys produce **Renin** (from juxtaglomerular cells), which converts Angiotensinogen to Angiotensin-I. They do not primarily convert Ang-I to Ang-II. * **Liver:** The liver synthesizes **Angiotensinogen**, the precursor protein. * **RBCs:** Red blood cells are not involved in the enzymatic pathways of the RAAS. **High-Yield NEET-PG Pearls:** * **Dual Function of ACE:** ACE is also known as **Kininase II**. Besides producing Angiotensin-II (a potent vasoconstrictor), it is responsible for the **degradation of Bradykinin** (a vasodilator). * **Clinical Correlation:** ACE Inhibitors (e.g., Enalapril) lead to an accumulation of Bradykinin in the lungs, which is the primary cause of the characteristic **dry cough** seen as a side effect. * **ACE2 vs. ACE:** ACE2 (a different enzyme) acts as the functional receptor for the **SARS-CoV-2** virus to enter host cells.

Q: Which reflex is associated with hyperinflation of the lung?

J-reflex. ### Explanation **Correct Option: A. J-reflex** The **J-reflex (Juxtacapillary reflex)** is mediated by **J-receptors** located in the alveolar walls, in close proximity to the pulmonary capillaries. These receptors are sensory nerve endings of the unmyelinated **vagus nerve (C-fibers)**. They are stimulated by **hyperinflation of the lungs**, pulmonary edema, pulmonary congestion, or pneumonia. * **Mechanism:** Stimulation leads to a reflex response characterized by **apnea followed by rapid shallow breathing (tachypnea)**, bradycardia, and hypotension. It is a protective mechanism to prevent lung overdistension. **Why other options are incorrect:** * **B. Cushing reflex:** This is a physiological nervous system response to **increased intracranial pressure (ICP)**. It is characterized by the "Cushing triad": hypertension, bradycardia, and irregular respirations. * **C. Bezold-Jarisch reflex:** This involves receptors in the **ventricles of the heart**. It is triggered by noxious chemical stimuli or stretch, leading to a triad of bradycardia, hypotension, and apnea. * **D. Bainbridge reflex:** Also known as the atrial distension reflex, it occurs when an increase in venous return stretches the **right atrium**, leading to an **increase in heart rate** to pump the excess blood. **High-Yield Clinical Pearls for NEET-PG:** * **Hering-Breuer Inflation Reflex:** Often confused with the J-reflex, this is triggered by stretch receptors in the smooth muscles of the airways to **terminate inspiration** and prevent over-inflation. * **J-receptors** are specifically sensitive to **interstitial volume changes** (e.g., pulmonary edema), which is why patients with left heart failure experience rapid shallow breathing. * **Key Stimulant:** Chemicals like **Capsaicin** can also pharmacologically trigger J-receptors.

Q: Which of the following factors does NOT cause a rightward shift of the oxygen-hemoglobin dissociation curve?

Decreased carbon dioxide. ### Explanation The oxygen-hemoglobin (O2-Hb) dissociation curve represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **rightward shift** indicates a **decreased affinity** of hemoglobin for oxygen, meaning oxygen is more easily released to the tissues. **Why "Decreased Carbon Dioxide" is the Correct Answer:** A decrease in $PCO_2$ (hypocapnia) causes a **leftward shift** of the curve. According to the **Bohr Effect**, lower levels of $CO_2$ (and the resulting increase in pH) increase hemoglobin's affinity for oxygen, making it bind more tightly and preventing its release. This typically occurs in the lungs. **Analysis of Incorrect Options (Factors causing a Rightward Shift):** * **Increased Hydrogen Ions (Decreased pH):** An acidic environment (acidosis) stabilizes the "Tense" (T) state of hemoglobin, promoting oxygen unloading. * **Increased Temperature:** Higher temperatures (as seen in exercising muscle or fever) weaken the bond between hemoglobin and oxygen, shifting the curve to the right to meet metabolic demands. * **Increased 2,3-BPG:** This byproduct of glycolysis binds to the beta chains of deoxyhemoglobin, stabilizing the T-state and facilitating oxygen release. Levels increase during chronic hypoxia or high-altitude adaptation. **NEET-PG High-Yield Pearls:** * **Mnemonic for Right Shift:** "**CADET**, face Right!" (**C**- $CO_2$ increase, **A**- Acidosis, **D**- 2,3-DPG/BPG increase, **E**- Exercise, **T**- Temperature increase). * **Fetal Hemoglobin (HbF):** Causes a **Left Shift** because it does not bind 2,3-BPG effectively, allowing the fetus to "pull" oxygen from maternal blood. * **P50 Value:** The $PO_2$ at which Hb is 50% saturated. A right shift **increases** the P50 (normal is ~26.7 mmHg).

Question 1

Which of the following best characterizes the pulmonary circulation?

Accepted Answer

Flow - High, Pressure - Low, Resistance - Low, Compliance - High

Answer

Flow - Low, Pressure - High, Resistance - Low, Compliance - High

Answer

Flow - High, Pressure - Low, Resistance - High, Compliance - Low

Answer

Flow - Low, Pressure - Low, Resistance - Low, Compliance - High

Question 2

Arterial PO2 is decreased in hypoxia due to which of the following conditions?

Accepted Answer

COPD (Chronic Obstructive Pulmonary Disease)

Answer

Cyanide poisoning

Answer

Carbon monoxide poisoning

Answer

Shock

Question 3

The following set of diagrams show the relationship between alveolar ventilation and arterial oxygen tension. Which diagram describes the situation when pO2 changes acutely over a range of 0-160 mm Hg, while pCO2 remains normal?

Accepted Answer

Curve D

Answer

Curve A

Answer

Curve B

Answer

Curve C

Question 4

The functional residual capacity is best defined as the sum of which two lung volumes?

Accepted Answer

Residual Volume and Expiratory Reserve Volume

Answer

Tidal volume and Inspiratory Reserve volume

Answer

Residual Volume and Inspiratory Reserve Volume

Answer

Tidal volume, Inspiratory Reserve volume, and Expiratory Reserve Volume

Question 5

Dead space is increased by all, except:

Accepted Answer

Endotracheal intubation

Answer

Anticholinergic drugs

Answer

Standing

Answer

Hyperextension of neck

Question 6

The oxygen buffer function of hemoglobin is related to which of the following?

Accepted Answer

Dissociation curve shape

Answer

Haldane effect

Answer

Bohr effect

Answer

Respiratory exchange ratio

Question 7

Which spirometry feature is characteristic of asthma?

Accepted Answer

FEV1/FEV ratio shows a downward trend

Answer

FEV shows an upward trend

Answer

PEF shows an upward trend

Answer

RV shows a downward trend

Question 8

Conversion of angiotensin-I to angiotensin-II occurs in which organ?

Accepted Answer

Lung

Answer

Kidney

Answer

Liver

Answer

RBCs

Question 9

Which reflex is associated with hyperinflation of the lung?

Accepted Answer

J-reflex

Answer

Cushing reflex

Answer

Bezold-Jaisch reflex

Answer

Bainbridge reflex

Question 10

Which of the following factors does NOT cause a rightward shift of the oxygen-hemoglobin dissociation curve?

Accepted Answer

Decreased carbon dioxide

Answer

Increased hydrogen ions

Answer

Increased temperature

Answer

Increased 2,3-bisphosphoglycerate (BPG)

Respiratory System — MCQs

Respiratory System — MCQs

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