Respiratory System Practice Questions

Q: Compared to the base, the apex of the upright human lung has:

A higher PO2. In the upright lung, both ventilation (V) and perfusion (Q) decrease from the base to the apex due to gravity. However, **perfusion decreases much more steeply than ventilation**. This results in a **higher Ventilation-Perfusion (V/Q) ratio at the apex** (~3.3) compared to the base (~0.6). **Why Option A is Correct:** Because the apex is "over-ventilated" relative to its blood flow (high V/Q), less oxygen is extracted from the alveoli per unit of ventilation. This leads to a **higher alveolar and end-capillary PO2** (approx. 130 mmHg at the apex vs. 89 mmHg at the base). **Why Other Options are Incorrect:** * **B & D:** Both ventilation and blood flow are **lowest at the apex** and highest at the base. Gravity pulls blood and lung tissue downward; the base is more compliant and better perfused. * **C:** Due to the high V/Q ratio at the apex, more CO2 is washed out, leading to a **lower PCO2**. A lower PCO2 results in a **higher (more alkaline) pH** in the end-capillary blood, not lower. **High-Yield Clinical Pearls for NEET-PG:** * **West Zones:** The apex represents Zone 1 (PA > Pa > Pv), though in healthy individuals, it is usually a functional Zone 2. * **Tuberculosis:** *Mycobacterium tuberculosis* has a predilection for the lung apices because the **higher PO2** provides a favorable environment for this obligate aerobe. * **V/Q Summary:** At the apex, V/Q is high (↑PO2, ↓PCO2, ↑pH). At the base, V/Q is low (↓PO2, ↑PCO2, ↓pH).

Q: Volume of air taken in and given out during normal respiration is referred to as:

Tidal Volume (TV). **Explanation:** The correct answer is **Tidal Volume (TV)**. **1. Why Tidal Volume is correct:** Tidal Volume is defined as the volume of air inspired or expired during a single, normal, quiet respiratory cycle. In a healthy adult male, the average value is approximately **500 mL**. It represents the rhythmic "ebb and flow" of breathing at rest, similar to the tides of the ocean. **2. Why other options are incorrect:** * **Inspiratory Reserve Volume (IRV):** This is the maximum extra volume of air that can be inspired *over and above* the normal tidal volume (approx. 2500–3000 mL). It is used during deep or forced inspiration. * **Expiratory Reserve Volume (ERV):** This is the maximum extra volume of air that can be expired by forceful expiration *after* the end of a normal tidal expiration (approx. 1000–1100 mL). * **Vital Capacity (VC):** This is a "capacity" (sum of two or more volumes). It is the maximum amount of air a person can expel from the lungs after first filling the lungs to their maximum extent ($VC = IRV + TV + ERV$). **3. NEET-PG High-Yield Pearls:** * **Minute Ventilation:** Calculated as $TV \times \text{Respiratory Rate}$. (e.g., $500 \text{ mL} \times 12 \text{ bpm} = 6 \text{ L/min}$). * **Alveolar Ventilation:** This is more clinically significant than Minute Ventilation as it accounts for **Anatomic Dead Space** (approx. 150 mL). Formula: $(TV - \text{Dead Space}) \times \text{Respiratory Rate}$. * **Measurement:** All lung volumes and capacities can be measured by **Spirometry**, *except* for Residual Volume (RV), Functional Residual Capacity (FRC), and Total Lung Capacity (TLC). These require helium dilution or body plethysmography.

Q: A shift to the right of the oxygen dissociation curve is caused by all of the following, EXCEPT:

Decrease in 2,3-bisphosphoglycerate (2,3-BPG). **Explanation:** The Oxygen Dissociation Curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **"Shift to the Right"** indicates a decreased affinity of hemoglobin for oxygen, meaning oxygen is more easily released to the tissues. **Why Option C is the Correct Answer:** **2,3-Bisphosphoglycerate (2,3-BPG)** is a byproduct of glycolysis in RBCs that binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state and promoting oxygen release. Therefore, an **increase** in 2,3-BPG shifts the curve to the right. Conversely, a **decrease** in 2,3-BPG (as seen in stored blood) increases hemoglobin's affinity for oxygen, shifting the curve to the **left**. Since the question asks for the exception, a decrease in 2,3-BPG is the correct choice. **Analysis of Incorrect Options:** * **Option A (Fall in pH):** A decrease in pH (acidosis) or an increase in $PCO_2$ reduces hemoglobin's affinity for oxygen. This is known as the **Bohr Effect**, which shifts the curve to the **right**. * **Option B (Rise in temperature):** Increased metabolic activity (e.g., exercise or fever) raises local temperature, which denatures the bond between oxygen and hemoglobin, shifting the curve to the **right** to facilitate unloading. **High-Yield NEET-PG Pearls:** * **CADET, face Right!:** A useful mnemonic for factors shifting the curve to the **Right**: **C**O2 increase, **A**cidosis, **D**PG (2,3-BPG) increase, **E**xercise, **T**emperature increase. * **Fetal Hemoglobin (HbF):** Shifts the curve to the **Left** because it lacks beta chains and does not bind 2,3-BPG effectively, allowing the fetus to pull oxygen from maternal blood. * **Carbon Monoxide (CO):** Shifts the curve to the **Left** and changes it from sigmoidal to hyperbolic, preventing oxygen release at tissues.

Q: Which of the following is true about the hemoglobin-oxygen dissociation curve?

Acidosis shifts the oxygen dissociation curve to the right.. The hemoglobin-oxygen dissociation curve (ODC) is a sigmoid-shaped graph representing the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. **Explanation of the Correct Option:** **Option A** is correct because **Acidosis** (increased $H^+$ concentration) decreases hemoglobin's affinity for oxygen, causing it to release $O_2$ more readily to the tissues. This phenomenon is known as the **Bohr Effect**. On the graph, a decrease in affinity is represented by a **shift to the right**, meaning a higher $PO_2$ is required to achieve the same level of saturation. **Analysis of Incorrect Options:** * **Option B:** Increased $CO_2$ (Hypercapnia) actually shifts the curve to the **right**, not the left. Like $H^+$, $CO_2$ stabilizes the "Tense" (T) state of hemoglobin, promoting oxygen unloading. * **Option C:** Chronic hypoxia (such as at high altitudes) leads to an increase in **2,3-BPG** production, which shifts the curve to the **right** to facilitate oxygen delivery to tissues. * **Option D:** **2,3-DPG (or 2,3-BPG)** is a critical regulator; it binds to the beta chains of hemoglobin and shifts the curve to the **right**. **High-Yield NEET-PG Pearls:** * **Mnemonic for Right Shift (CADET, face Right!):** **C**O2 increase, **A**cidosis, **D**PG (2,3-BPG) increase, **E**xercise, and **T**emperature increase. * **Left Shift:** Occurs in Fetal Hemoglobin (HbF), CO poisoning, Methemoglobinemia, and Hypothermia. * **P50 Value:** The $PO_2$ at which hemoglobin is 50% saturated. A right shift **increases** the P50 (Normal P50 $\approx$ 26.6 mmHg).

Q: Which compound shifts the oxygen dissociation curve to the right?

2,3 DPG. **Explanation:** The oxygen dissociation curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin ($Hb$). A **shift to the right** indicates a decreased affinity of hemoglobin for oxygen, facilitating oxygen unloading to the tissues. **Why 2,3-DPG is correct:** **2,3-Diphosphoglycerate (2,3-DPG)**, also known as 2,3-BPG, is a byproduct of the Rappaport-Luebering shunt in glycolysis within erythrocytes. It binds to the beta chains of deoxyhemoglobin, stabilizing the **T (Tense) state**. This reduces hemoglobin's affinity for oxygen, shifting the curve to the right and promoting oxygen release at the tissue level. Levels of 2,3-DPG increase during chronic hypoxia, high-altitude adaptation, and anemia. **Analysis of Incorrect Options:** * **A & C (Phosphoglycerate / 1,3-DPG):** These are intermediate metabolites in the Embden-Meyerhof pathway (glycolysis). While 1,3-DPG is the precursor to 2,3-DPG, these compounds themselves do not bind to hemoglobin or significantly influence its oxygen affinity. * **D (Glyceraldehyde):** This is a simple sugar (triose) involved in carbohydrate metabolism but has no physiological role in modulating the oxygen-hemoglobin bond. **High-Yield Clinical Pearls for NEET-PG:** * **Factors shifting the curve to the RIGHT (CADET, face Right!):** **C**O2 increase, **A**cidosis ($H^+$), **D**PG (2,3-DPG) increase, **E**xercise, and **T**emperature increase. * **Fetal Hemoglobin (HbF):** Shifts the curve to the **left** because it has a lower affinity for 2,3-DPG (due to gamma chains instead of beta chains), allowing the fetus to pull oxygen from maternal blood. * **Stored Blood:** 2,3-DPG levels decrease in stored blood, shifting the curve to the **left** and potentially impairing oxygen delivery upon massive transfusion.

Q: Which of the following conditions is NOT associated with a decrease in Residual Volume?

Emphysema. ### Explanation **Residual Volume (RV)** is the volume of air remaining in the lungs after a maximal forceful expiration. Changes in RV are primarily determined by the lung's elastic recoil and airway patency. #### 1. Why Emphysema is the Correct Answer In **Emphysema** (a type of Chronic Obstructive Pulmonary Disease), there is a destruction of alveolar walls and loss of elastic recoil. This leads to two major consequences: * **Air Trapping:** The loss of radial traction causes small airways to collapse during expiration. * **Hyperinflation:** The lungs become overly compliant and cannot effectively expel air. Consequently, **Residual Volume (RV), Functional Residual Capacity (FRC), and Total Lung Capacity (TLC) are all increased** in emphysema, not decreased. #### 2. Analysis of Incorrect Options (Conditions with Decreased RV) Options B, C, and D represent **Restrictive Lung Patterns** or space-occupying lesions that reduce the available lung volume: * **Interstitial Lung Disease (ILD):** Increased elastic recoil (stiff lungs) pulls the airways open but limits expansion, leading to a global decrease in all lung volumes, including RV. * **Bacterial Pneumonia & Lung Abscess:** These are "filling disorders" where inflammatory exudate, pus, or consolidation replaces air spaces. This physical displacement of air-containing tissue results in a decrease in RV. #### 3. NEET-PG High-Yield Pearls * **Obstructive Diseases (Asthma, COPD):** RV ↑, FRC ↑, TLC ↑, FEV1/FVC ratio ↓. * **Restrictive Diseases (Fibrosis, Kyphoscoliosis):** RV ↓, FRC ↓, TLC ↓, FEV1/FVC ratio is Normal or ↑. * **RV Measurement:** RV cannot be measured by simple spirometry; it requires **Helium Dilution, Nitrogen Washout, or Body Plethysmography.** * **Aging:** RV naturally increases with age due to the loss of elastic recoil, even in healthy individuals.

Q: What is true about Maximum Mid-expiratory Flow Rate (MMEFR)?

All of the above. **Explanation:** **Maximum Mid-Expiratory Flow Rate (MMEFR)**, also known as **FEF 25–75%**, is a sensitive index of airway obstruction, particularly in the smaller, peripheral airways. 1. **Why Option D is correct:** * **Value (Option A):** The normal average value for a healthy adult is approximately **150–300 Liters per minute**. While it varies by age and gender, 150 L/min is considered the standard baseline for clinical assessment. * **Effort (Option B):** MMEFR is derived from the Forced Vital Capacity (FVC) maneuver. It requires the patient to inhale to Total Lung Capacity (TLC) and then exhale with **maximum voluntary effort** into a spirometer. * **Definition (Option C):** It represents the average flow rate during the middle half (25% to 75%) of a forced expiration. Conceptually, it measures the "maximum breathing capacity" specifically during this mid-expiratory phase, reflecting the patency of small airways. 2. **Clinical Significance:** * Unlike FEV1, which is effort-dependent and reflects large airway function, MMEFR is **effort-independent** in its later stages and is the most sensitive indicator for **early obstructive lung disease** (e.g., early stages of COPD or asthma) where small airways are affected first. **High-Yield NEET-PG Pearls:** * **Small Airway Disease:** MMEFR is the best test to detect "silent zone" (small airway) involvement. * **Effort Independence:** The middle and terminal parts of the expiratory flow are independent of the effort once the maximum flow has been reached. * **Normal FEV1/FVC:** In early obstructive disease, the FEV1/FVC ratio may be normal, but the MMEFR will be significantly reduced.

Q: What is the normal partial pressure of carbon dioxide (pCO2) in exhaled air?

27 mm Hg. The partial pressure of carbon dioxide in exhaled air ($P_E CO_2$) is approximately **27 mm Hg**. This value is a result of the mixing of alveolar air with air from the anatomical dead space. ### **Detailed Explanation** 1. **The Concept of Mixing:** During expiration, the first portion of air expelled comes from the **anatomical dead space** (trachea and bronchi), where $PCO_2$ is nearly **0 mm Hg** (similar to atmospheric air). The latter portion is **alveolar air**, which has a $PCO_2$ of **40 mm Hg**. 2. **The Resultant Value:** The total exhaled air (mixed expired air) is a combination of these two. Since dead space accounts for roughly one-third of a normal tidal volume, the $PCO_2$ is diluted from 40 mm Hg down to approximately **27–28 mm Hg**. ### **Analysis of Options** * **A. 36 mm Hg:** This is too high for mixed expired air; it is closer to the $PCO_2$ of end-tidal air (which represents pure alveolar air). * **B. 27 mm Hg (Correct):** This represents the average $PCO_2$ in a full breath of expired air after dilution by dead space. * **C. 40 mm Hg:** This is the $PCO_2$ of **alveolar air** and **systemic arterial blood ($PaCO_2$)**. * **D. 17 mm Hg:** This value is too low and would only be seen in states of extreme hyperventilation or increased dead space ventilation. ### **NEET-PG High-Yield Pearls** * **Bohr Equation:** Uses the difference between $PaCO_2$ (40) and $P_E CO_2$ (27) to calculate the **Physiological Dead Space**. * **End-Tidal $CO_2$ ($EtCO_2$):** In clinical anesthesia, $EtCO_2$ monitors the very last portion of expired air. It is usually **35–40 mm Hg**, reflecting alveolar $CO_2$ levels. * **Inspired Air $PCO_2$:** Is negligible (~0.3 mm Hg).

Question 1

Compared to the base, the apex of the upright human lung has:

Accepted Answer

A higher PO2

Answer

A higher ventilation

Answer

A lower pH in end-capillary blood

Answer

A higher blood flow

Question 2

Volume of air taken in and given out during normal respiration is referred to as:

Accepted Answer

Tidal Volume (TV)

Answer

Inspiratory Reserve Volume (IRV)

Answer

Expiratory Reserve Volume (ERV)

Answer

Vital Capacity (VC)

Question 3

Hypoxic pulmonary vasoconstriction:

Accepted Answer

Is released in the transition from placental to air respiration

Answer

Depends more on the PO2 of mixed venous blood than alveolar gas

Answer

Involves CO2 uptake in vascular smooth muscle

Answer

Shunts blood flow from well-ventilated regions of diseased lungs

Question 4

A shift to the right of the oxygen dissociation curve is caused by all of the following, EXCEPT:

Accepted Answer

Decrease in 2,3-bisphosphoglycerate (2,3-BPG)

Answer

Fall in pH

Answer

Rise in temperature

Answer

None of the above

Question 5

Which of the following is true about the hemoglobin-oxygen dissociation curve?

Accepted Answer

Acidosis shifts the oxygen dissociation curve to the right.

Answer

Increased carbon dioxide shifts the curve to the left.

Answer

Hypoxia shifts the curve to the left.

Answer

2,3-diphosphoglycerate has no effect on the curve.

Question 6

Which compound shifts the oxygen dissociation curve to the right?

Accepted Answer

2,3 DPG

Answer

Phosphoglycerate

Answer

1,3 DPG

Answer

Glyceraldehyde

Question 7

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

Accepted Answer

Emphysema

Answer

Bacterial pneumonia

Answer

Interstitial lung disease

Answer

Lung abscess

Question 8

What is true about Maximum Mid-expiratory Flow Rate (MMEFR)?

Accepted Answer

All of the above

Answer

150 liters per minute

Answer

Measured with maximum voluntary effort

Answer

Maximum breathing capacity per minute

Question 9

Medullary chemoreceptors are primarily sensitive to which of the following?

Accepted Answer

H+ concentration in the cerebrospinal fluid (CSF)

Answer

CO2 concentration in the cerebrospinal fluid (CSF)

Answer

H+ concentration in the blood

Answer

CO2 concentration in the blood

Question 10

What is the normal partial pressure of carbon dioxide (pCO2) in exhaled air?

Accepted Answer

27 mm Hg

Answer

36 mm Hg

Answer

40 mm Hg

Answer

17 mm Hg

Respiratory System — MCQs

Respiratory System — MCQs

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