Respiratory System Practice Questions

Q: Haemoglobin is the major buffer in blood. Bicarbonate ions diffuse out of erythrocytes into plasma in exchange for which ion?

Chloride ion. This question tests the understanding of the **Chloride Shift (Hamburger Phenomenon)**, a vital mechanism for CO₂ transport and acid-base balance. ### Explanation of the Correct Answer When CO₂ enters erythrocytes, it reacts with water (catalyzed by carbonic anhydrase) to form carbonic acid, which dissociates into **H⁺** and **HCO₃⁻**. 1. The H⁺ ions are buffered by deoxyhemoglobin. 2. As HCO₃⁻ (bicarbonate) concentrations rise, they diffuse out of the cell into the plasma along a concentration gradient. 3. To maintain **electrical neutrality**, an equivalent amount of negative charge must enter the cell. This is achieved by the influx of **Chloride ions (Cl⁻)** via the **Anion Exchanger 1 (Band 3 protein)**. This process is the Chloride Shift. ### Why Other Options are Incorrect * **A. Potassium:** Potassium is the primary intracellular cation. While it maintains osmotic balance, it does not exchange directly for bicarbonate during CO₂ transport. * **B. Phosphate:** Intracellular phosphates act as buffers, but they do not participate in the rapid transmembrane exchange required for systemic CO₂ transport. * **C. Carbonic acid:** This is an intermediate molecule (H₂CO₃) that quickly dissociates; it does not exist as a transportable ion in this exchange. ### High-Yield NEET-PG Pearls * **Reverse Chloride Shift:** Occurs in the **lungs**, where Cl⁻ moves *out* of the RBC and HCO₃⁻ moves *in* to be converted back to CO₂ for exhalation. * **Water Movement:** When Cl⁻ enters the RBC (in systemic tissues), osmotic pressure increases, causing water to enter the cell. Consequently, **venous RBCs are slightly larger (higher MCV)** than arterial RBCs. * **Haldane Effect:** Deoxygenation of blood increases its ability to carry CO₂, primarily because deoxyhemoglobin is a better buffer for H⁺ than oxyhemoglobin.

Q: In the ventilation-perfusion (V/Q) ratio curve for the normal lung, if the V/Q ratio is decreased, what will be the effect on pCO2 and pO2?

pCO2 increases, pO2 decreases. ***pCO2 increases, pO2 decreases*** - When **V/Q ratio decreases** (low ventilation relative to perfusion), blood spends more time in contact with poorly ventilated alveoli, leading to **inadequate CO2 removal** and **insufficient O2 uptake**. - This creates a **shunt-like condition** where mixed venous blood with high pCO2 and low pO2 values dominates the gas exchange, resulting in increased pCO2 and decreased pO2. *pCO2 decreases, pO2 increases* - This pattern occurs when **V/Q ratio increases** (high ventilation relative to perfusion), creating **dead space-like conditions**. - With excessive ventilation relative to blood flow, **CO2 is efficiently removed** and **O2 equilibrates** with alveolar air, opposite to the decreased V/Q scenario. *pCO2 decreases, pO2 decreases* - This combination is physiologically inconsistent as **CO2 and O2 changes typically occur in opposite directions** in V/Q mismatch scenarios. - Decreased pCO2 suggests **hyperventilation effect**, while decreased pO2 suggests **hypoventilation**, creating a contradictory pattern. *pCO2 increases, pO2 increases* - This pattern is physiologically impossible in **V/Q mismatch conditions** as impaired ventilation cannot simultaneously cause CO2 retention and O2 enrichment. - **CO2 and O2 levels move in opposite directions** during V/Q ratio changes due to their different **solubility** and **binding characteristics** in blood.

Q: The given graph likely depicts which of the following conditions?

Emphysema. ***Emphysema*** - Shows classic **obstructive pattern** with reduced **FEV1** and **FEV1/FVC ratio** (<70%), indicating airflow limitation. - The **scooped-out expiratory limb** on flow-volume loop is pathognomonic for emphysema due to **loss of elastic recoil** and **airway collapse**. *Interstitial lung disease* - Would show a **restrictive pattern** with reduced **total lung capacity (TLC)** and **vital capacity** but preserved FEV1/FVC ratio. - Flow-volume loop typically shows a **narrow, tall pattern** rather than the obstructive scooping seen here. *Normal study* - Normal spirometry shows **FEV1/FVC ratio >70%** with smooth, symmetric flow-volume loop curves. - **Peak expiratory flow** and lung volumes would be within normal predicted ranges for age, height, and gender. *Kyphosis* - Causes a **restrictive pattern** due to **chest wall deformity** limiting lung expansion, not airflow obstruction. - Would show reduced lung volumes but **preserved FEV1/FVC ratio**, unlike the obstructive pattern depicted.

Q: Pulmonary vasoconstriction is caused by:

Hypoxia. **Explanation:** The correct answer is **Hypoxia**. This phenomenon is known as **Hypoxic Pulmonary Vasoconstriction (HPV)**, a unique physiological mechanism in the lungs. **1. Why Hypoxia is correct:** In most systemic tissues, hypoxia causes vasodilation to increase blood flow. However, in the lungs, the response is the opposite. When a specific area of the lung is poorly ventilated (low $P_aO_2$), the local pulmonary arterioles constrict. This serves as a protective mechanism to **shunt blood away** from poorly ventilated alveoli toward well-ventilated ones, thereby optimizing **Ventilation-Perfusion (V/Q) matching** and preventing systemic hypoxemia. The mechanism involves the inhibition of oxygen-sensitive potassium channels in pulmonary vascular smooth muscle cells, leading to depolarization and calcium influx. **2. Why the other options are incorrect:** * **Prostacyclin ($PGI_2$):** This is a potent **vasodilator** and inhibitor of platelet aggregation. It is often used therapeutically to treat pulmonary hypertension. * **Alpha-2 stimulation:** While Alpha-1 stimulation typically causes vasoconstriction, Alpha-2 receptors in the vasculature often mediate **vasodilation** (via endothelial NO release) or have negligible effects compared to the profound constriction caused by hypoxia. * **Histamine:** In the pulmonary circulation, histamine generally acts as a **vasodilator** (via H2 receptors), although it is a potent bronchoconstrictor. **High-Yield Clinical Pearls for NEET-PG:** * **Global Hypoxia:** If the entire lung is hypoxic (e.g., at high altitudes), generalized pulmonary vasoconstriction occurs, leading to **High Altitude Pulmonary Edema (HAPE)** and pulmonary hypertension. * **Nitric Oxide (NO):** The most potent endogenous pulmonary vasodilator. * **Other Vasoconstrictors:** Hypercapnia (High $CO_2$), Acidosis (Low pH), Endothelin, and Thromboxane $A_2$.

Q: Which of the following statements is FALSE regarding the oxygen dissociation curve?

An increase in pH shifts the curve to the right.. ### Explanation The Oxygen Dissociation Curve (ODC) describes the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin ($SaO_2$). **1. Why Option C is the Correct (False) Statement:** The shift of the ODC is determined by the affinity of hemoglobin for oxygen. A **right shift** indicates decreased affinity (easier unloading of $O_2$ to tissues), while a **left shift** indicates increased affinity. An **increase in pH (Alkalosis)** causes a **left shift**. Conversely, a decrease in pH (Acidosis/increased $[H^+]$) causes a right shift; this is known as the **Bohr Effect**. Therefore, the statement that an increase in pH shifts the curve to the right is false. **2. Analysis of Other Options:** * **Option A:** The curve is **sigmoid (S-shaped)** due to the "cooperative binding" property of hemoglobin. * **Option B:** This describes **positive cooperativity**. When the first heme group binds $O_2$, it causes a conformational change in the hemoglobin tetramer (from T-state to R-state), significantly increasing the affinity of the remaining heme groups for $O_2$. * **Option C:** A **fall in temperature** decreases the kinetic energy of molecules, strengthening the bond between hemoglobin and oxygen, thus shifting the curve to the **left**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Right Shift (Mnemonic: "CADET, face Right!"):** * **C** – $CO_2$ increase * **A** – Acidosis ($H^+$ increase / pH decrease) * **D** – 2,3-DPG increase * **E** – Exercise * **T** – Temperature increase * **$P_{50}$ Value:** The $PO_2$ at which hemoglobin is 50% saturated. Normal value is **26.7 mmHg**. An increase in $P_{50}$ signifies a right shift. * **Fetal Hemoglobin (HbF):** Lacks beta chains (has gamma chains) and does not bind 2,3-DPG effectively, causing a **left shift** compared to adult hemoglobin (HbA).

Q: The shift of the oxygen dissociation curve to the left is facilitated by all except?

Decrease in pH. The **Oxygen-Hemoglobin Dissociation Curve** represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. ### **Why "Decrease in pH" is the Correct Answer** A **decrease in pH** (acidosis) indicates an increase in $H^+$ ion concentration. This stabilizes the "Tense" (T) state of hemoglobin, reducing its affinity for oxygen and causing the curve to shift to the **RIGHT**. This is known as the **Bohr Effect**. A right shift facilitates oxygen unloading to tissues, which is the opposite of what the question asks. ### **Analysis of Incorrect Options (Left Shift Factors)** A **Left Shift** indicates an increased affinity of hemoglobin for oxygen (holding onto $O_2$ more tightly). * **Fetal Hemoglobin (HbF):** HbF lacks the ability to bind effectively with 2,3-DPG. This results in a higher affinity for $O_2$ compared to adult hemoglobin (HbA), shifting the curve to the **left** to ensure oxygen uptake from the placenta. * **Decrease in 2,3-DPG:** 2,3-Bisphosphoglycerate normally stabilizes the T-state. Its absence or decrease shifts the curve to the **left**. * **Decrease in Temperature:** Lower temperatures stabilize the bond between oxygen and hemoglobin, increasing affinity and shifting the curve to the **left**. ### **High-Yield NEET-PG Pearls** * **Mnemonic for Right Shift (CADET, face Right!):** * **C** – $CO_2$ increase * **A** – Acidosis (Decrease in pH) * **D** – 2,3-**D**PG increase * **E** – Exercise * **T** – Temperature increase * **P50 Value:** The $PO_2$ at which Hb is 50% saturated. Normal is **26.6 mmHg**. A **Right shift** increases P50; a **Left shift** decreases P50. * **Carbon Monoxide (CO):** Causes a **Left shift** and a downward shift (decreases oxygen-carrying capacity).

Q: Routine spirometry cannot estimate which of the following lung volumes or capacities?

Functional Residual Capacity (FRC). **Explanation:** The correct answer is **Functional Residual Capacity (FRC)**. **1. Why FRC is the correct answer:** Routine spirometry measures the volume of air that can be moved into or out of the lungs. It cannot measure any lung volume that remains in the chest after a maximal expiration. This "unmeasurable" volume is the **Residual Volume (RV)**. Since FRC is the sum of Residual Volume and Expiratory Reserve Volume (**FRC = RV + ERV**), it cannot be determined by simple spirometry. To measure FRC, specialized techniques like **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography** are required. **2. Why the other options are incorrect:** * **Vital Capacity (VC):** This is the maximum volume of air a person can exhale after a maximum inhalation. Since it involves active air movement, it is easily measured by spirometry. * **Forced Expiratory Volume (FEV):** This measures the volume of air exhaled during specific time intervals (e.g., FEV1) of a forced breath. It is a dynamic parameter measured routinely via spirometry to diagnose obstructive lung diseases. * **Expiratory Reserve Volume (ERV):** This is the extra volume of air that can be forcefully expired after a normal tidal expiration. Since this air leaves the lungs, the spirometer can record it. **3. NEET-PG High-Yield Pearls:** * **The "Rule of RV":** Any capacity that includes Residual Volume cannot be measured by spirometry. This includes **FRC** and **Total Lung Capacity (TLC)**. * **Gold Standard:** Body Plethysmography is the most accurate method for measuring FRC, especially in patients with "trapped air" (e.g., Emphysema), where gas dilution methods may underestimate volumes. * **Closing Capacity:** This is another parameter that cannot be measured by routine spirometry (Closing Capacity = Closing Volume + RV).

Q: What is the haemoglobin derivative formed due to the reaction of CO2 with blood?

Carbaminohemoglobin. ### Explanation **1. Why Carbaminohemoglobin is Correct:** Carbon dioxide ($CO_2$) is transported in the blood in three forms: as bicarbonate ions (70%), dissolved in plasma (7%), and bound to hemoglobin (23%). When $CO_2$ reacts with hemoglobin, it binds specifically to the **amino groups** of the globin chains (not the heme iron) to form **Carbaminohemoglobin**. This reaction is reversible and depends on the partial pressure of $CO_2$ ($PCO_2$). In the tissues, high $PCO_2$ favors formation; in the lungs, low $PCO_2$ favors dissociation. **2. Analysis of Incorrect Options:** * **Carboxyhemoglobin:** Formed when **Carbon Monoxide (CO)** binds to the heme iron. CO has an affinity for hemoglobin 210–250 times higher than oxygen, leading to tissue hypoxia. * **Methemoglobin:** Formed when the iron in heme is oxidized from the **ferrous state ($Fe^{2+}$)** to the **ferric state ($Fe^{3+}$)**. It cannot bind oxygen effectively and causes a "chocolate-colored" appearance of blood. * **Reduced Hemoglobin (Deoxyhemoglobin):** This is simply hemoglobin that is not bound to oxygen. While it has a higher affinity for $CO_2$ (Haldane Effect), it is not the name of the $CO_2$ derivative itself. **3. NEET-PG Clinical Pearls:** * **Haldane Effect:** Deoxygenation of the blood increases its ability to carry $CO_2$. This is crucial for $CO_2$ loading at the tissue level. * **Bohr Effect:** Increased $PCO_2$ and decreased pH shift the oxygen-dissociation curve to the **right**, facilitating oxygen unloading to tissues. * **Binding Site:** Remember, $O_2$ and $CO$ bind to the **Heme (Iron)**, while $CO_2$ and $H^+$ bind to the **Globin (Protein)** portion.

Question 1

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

Accepted Answer

Hypokalemia

Answer

Hyperkalemia

Answer

Anemia

Answer

Metabolic alkalosis

Question 2

Haemoglobin is the major buffer in blood. Bicarbonate ions diffuse out of erythrocytes into plasma in exchange for which ion?

Accepted Answer

Chloride ion

Answer

Potassium

Answer

Phosphate

Answer

Carbonic acid

Question 3

In the ventilation-perfusion (V/Q) ratio curve for the normal lung, if the V/Q ratio is decreased, what will be the effect on pCO2 and pO2?

Accepted Answer

pCO2 increases, pO2 decreases

Answer

pCO2 decreases, pO2 increases

Answer

pCO2 decreases, pO2 decreases

Answer

pCO2 increases, pO2 increases

Question 4

The given graph likely depicts which of the following conditions?

Accepted Answer

Emphysema

Answer

Interstitial lung disease

Answer

Normal study

Answer

Kyphosis

Question 5

What causes the difference in the trajectory between the inspiratory loop and the expiratory loop in a flow-volume curve?

Accepted Answer

Difference in airway resistance during inspiration and expiration.

Answer

Difference in alveolar pressure during inspiration and expiration.

Answer

Difference in the concentration of surfactant during inspiration and expiration.

Answer

Inspiration is an active process and expiration is a passive process.

Question 6

Pulmonary vasoconstriction is caused by:

Accepted Answer

Hypoxia

Answer

Prostacyclin

Answer

Alpha-2 stimulation

Answer

Histamine

Question 7

Which of the following statements is FALSE regarding the oxygen dissociation curve?

Accepted Answer

An increase in pH shifts the curve to the right.

Answer

It is a sigmoid curve.

Answer

The combination of the first heme in the hemoglobin molecule with O2 increases the affinity of the second heme for O2.

Answer

A fall in temperature shifts the curve to the left.

Question 8

The shift of the oxygen dissociation curve to the left is facilitated by all except?

Accepted Answer

Decrease in pH

Answer

Fetal hemoglobin

Answer

Decrease in 2,3 DPG

Answer

Decrease in temperature

Question 9

Routine spirometry cannot estimate which of the following lung volumes or capacities?

Accepted Answer

Functional Residual Capacity (FRC)

Answer

Vital Capacity (VC)

Answer

Forced Expiratory Volume (FEV)

Answer

Expiratory Reserve Volume (ERV)

Question 10

What is the haemoglobin derivative formed due to the reaction of CO2 with blood?

Accepted Answer

Carbaminohemoglobin

Answer

Carboxyhemoglobin

Answer

Methemoglobin

Answer

Reduced haemoglobin

Respiratory System — MCQs

Respiratory System — MCQs

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