Respiratory System Practice Questions

Q: Which of the following is a cause of shock?

Stagnant hypoxia. **Explanation:** The core pathophysiology of **Shock** is defined as a state of generalized hypoperfusion where the delivery of oxygen and nutrients is insufficient to meet metabolic demands. **1. Why Stagnant Hypoxia is Correct:** Stagnant hypoxia (also known as ischemic hypoxia) occurs when the arterial oxygen content is normal, but the **blood flow to tissues is reduced**. In shock—whether cardiogenic (pump failure), hypovolemic (low volume), or obstructive—the cardiac output falls significantly. This leads to a "stagnant" flow of blood, preventing adequate oxygen delivery to the peripheral tissues despite normal hemoglobin levels and oxygen saturation. **2. Analysis of Incorrect Options:** * **Anemic Hypoxia:** Occurs when the oxygen-carrying capacity of the blood is reduced (e.g., anemia, CO poisoning). While it reduces oxygen delivery, it is not the primary mechanism defining shock. * **Hypoxic Hypoxia:** Characterized by low arterial $PO_2$ (e.g., high altitude, lung disease). The circulation is usually intact, but the blood itself is poorly oxygenated. * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize oxygen despite adequate delivery (e.g., Cyanide poisoning). The blood flow and oxygen content are normal, but the cellular respiratory chain is inhibited. **Clinical Pearls for NEET-PG:** * **V/Q Mismatch:** The most common cause of Hypoxic Hypoxia. * **Cyanosis:** Stagnant hypoxia often presents with **peripheral cyanosis** (increased oxygen extraction at tissues), whereas hypoxic hypoxia presents with **central cyanosis**. * **Shock Hallmark:** The transition from aerobic to **anaerobic metabolism**, leading to lactic acidosis, is the metabolic hallmark of stagnant hypoxia in shock.

Q: Which of the following oxygen-sensitive channels is present in peripheral chemoreceptors?

K+. ***K+***- **Oxygen-sensitive K+ channels**, specifically members of the **TASK-like potassium channels** family, are central to the response of **glomus cells** in the carotid body to **hypoxia**.- When oxygen levels fall, these channels are **inhibited**, reducing K+ efflux and causing the cell membrane to **depolarize**, initiating the signaling cascade.*Na+*- While **voltage-gated Na+ channels** are essential for action potential generation in the afferent nerve, they are not the primary channels that directly sense changes in **pO2** within the glomus cells.- The initial depolarizing signal stems from the inhibition of K+ channels, not the activation or inhibition of Na+ channels.*Ca++*- **Voltage-gated Ca++ channels** open in response to the **depolarization** caused by K+ channel inhibition upon hypoxia.- The resulting **calcium influx** is mandatory for the final step: triggering the release of **neurotransmitters** (e.g., dopamine, ATP) that signal the brainstem.*Cl-*- **Cl- channels** (Chloride channels) are present in glomus cells and help regulate cell volume and membrane potential, but they do not function as the mechanism's primary oxygen sensor.- The entire chemosensing process is primarily governed by the modulation of **cation** movement (K+ efflux and subsequent Ca++ influx) rather than chloride flux.

Q: Which of the following factors causes a rightward shift in the oxygen-hemoglobin dissociation curve?

Increase in CO₂. ***Increase in CO₂*** - An increase in the partial pressure of **carbon dioxide (PCO₂)** in the blood leads to a decrease in pH (increased H⁺ concentration), a phenomenon known as the **Bohr effect**. - This acidic environment stabilizes the **taut (T) state** of hemoglobin, reducing its affinity for oxygen and facilitating oxygen unloading to metabolically active tissues, thus causing a **rightward shift**. *Increase in O₂* - An increase in the partial pressure of **oxygen (PO₂)** represents a movement *along* the existing curve to the right, leading to a higher hemoglobin saturation percentage. - It does not alter the intrinsic affinity of hemoglobin for oxygen and therefore does not cause a shift of the entire curve. *Decrease in CO₂* - A decrease in **PCO₂** leads to an increase in blood pH (respiratory alkalosis), which increases hemoglobin's affinity for oxygen. - This increased affinity impairs oxygen release to tissues and causes a **leftward shift** of the curve, promoting oxygen uptake in the lungs. *Decrease in temperature* - A decrease in body **temperature** (hypothermia) increases the affinity of hemoglobin for oxygen. - This makes it more difficult for hemoglobin to release oxygen to the tissues, resulting in a **leftward shift** of the curve.

Q: Which of the following describes the chloride ion exchange in red blood cells, where bicarbonate ions are exchanged for chloride ions to maintain electrical neutrality?

Chloride shift. ***Chloride shift***- This is the term for the exchange of a **bicarbonate ion** ($ ext{HCO}_3^-$) moving out of the red blood cell for a **chloride ion** ($ ext{Cl}^-$) moving into the cell to maintain **electrical neutrality**. - It is essential for the efficient transport of **carbon dioxide** ($ ext{CO}_2$) from peripheral tissues to the lungs in the form of dissolved bicarbonate. *Haldane effect* - Describes the process where the unloading of **oxygen** in peripheral tissues increases the affinity of hemoglobin for **carbon dioxide** ($ ext{CO}_2$) and $ ext{H}^+$ (and vice versa in the lungs). - It primarily relates to the interaction between $ ext{O}_2$ saturation and $ ext{CO}_2$ binding, not the ion exchange itself. *Root effect* - This effect describes the decrease in the **oxygen carrying capacity** of hemoglobin caused by a drop in pH, often seen in fish. - It is a specialized form of the **Bohr effect**, but specifically refers to the non-sigmoidal shape of the $ ext{O}_2$-Hb curve at low pH. *Bohr effect* - This phenomenon explains that an increase in $ ext{PCO}_2$ or a decrease in pH (more **acidity**) shifts the oxygen-hemoglobin dissociation curve to the **right**. - This shift promotes the release of **oxygen** from hemoglobin to active tissues where $ ext{CO}_2$ production is high.

Q: What is the effect of pulmonary embolism on the V/Q ratio in alveoli distal to the obstructed pulmonary artery?

Increased V/Q ratio approaching infinity (dead space). ***Increased V/Q ratio approaching infinity (dead space)*** - In pulmonary embolism, an embolus obstructs a pulmonary artery, leading to a significant reduction or complete cessation of **perfusion (Q)** to the downstream lung tissue, while **ventilation (V)** remains unaffected. - This creates a V/Q mismatch where the ratio V/Q becomes very high, approaching infinity. This ventilated but unperfused lung region is known as **physiological dead space**. *Decreased V/Q ratio approaching zero* - A decreased V/Q ratio occurs when ventilation is impaired relative to perfusion (V<Q), resulting in a **low V/Q mismatch**. A true shunt is defined specifically as a V/Q ratio equal to zero, where there is no ventilation at all to a perfused unit. - Low V/Q mismatch (V/Q approaching but not equal to zero) is characteristic of conditions like **pneumonia**, **pulmonary edema**, or **atelectasis**, where alveoli are partially obstructed but still receive blood flow, whereas a true shunt (V/Q = 0) occurs when alveoli are completely unventilated yet still perfused. *Normal V/Q ratio* - Pulmonary embolism is a classic cause of a severe **V/Q mismatch**, specifically creating high V/Q units; therefore, the ratio in the affected area is not normal. - A normal V/Q ratio (approximately 0.8) implies well-matched ventilation and perfusion, which is the state PE directly disrupts. *Increased perfusion (Q) and decreased ventilation (V)* - This describes the opposite of what occurs in pulmonary embolism, where the primary problem is a **decrease in perfusion (Q)** due to the arterial blockage. - Increased perfusion with decreased ventilation would result in a **low V/Q ratio**, not the high V/Q dead space seen in PE.

Q: Which flow volume curve recording is shown below?

Variable extrathoracic obstruction. ***Variable extrathoracic obstruction*** - This flow-volume loop shows a **flattening of the inspiratory limb** (I) while the expiratory limb (E) remains relatively normal. - This pattern is characteristic of a **variable extrathoracic obstruction**, where the negative pressure during inspiration causes the airway to collapse, whereas the positive pressure during expiration helps keep the airway open. *Parenchymal obstructive airway disease* - This typically presents as a **"scooped out" appearance** of the expiratory limb due to airflow limitation throughout expiration, which is not seen here. - The inspiratory limb would generally be preserved or less affected compared to the expiratory limb. *Restrictive airway disease* - Flow-volume loops in restrictive disease show a **smaller loop overall**, indicating reduced lung volumes, but the general shape is typically preserved (narrower and taller). - Both inspiratory and expiratory limbs would be proportionately reduced, which is different from the isolated inspiratory flattening shown. *Variable intrathoracic obstruction* - This type of obstruction would cause **flattening of the expiratory limb** of the flow-volume loop because the positive intrathoracic pressure during expiration compresses an intrathoracic lesion. - The inspiratory limb would largely be unaffected, which is the opposite of the pattern observed in the provided image.

Question 1

Which of the following is a cause of shock?

Accepted Answer

Stagnant hypoxia

Answer

Anemic hypoxia

Answer

Hypoxic hypoxia

Answer

Histotoxic hypoxia

Question 2

What is the pressure gradient during inspiration?

Accepted Answer

Intrapleural pressure

Answer

Transpulmonary pressure

Answer

Trans-chest wall pressure

Answer

Alveolar pressure

Question 3

Which of the following oxygen-sensitive channels is present in peripheral chemoreceptors?

Accepted Answer

K+

Answer

Ca++

Answer

Na+

Answer

Cl-

Question 4

Which of the following factors causes a rightward shift in the oxygen-hemoglobin dissociation curve?

Accepted Answer

Increase in CO₂

Answer

Increase in O₂

Answer

Decrease in CO₂

Answer

Decrease in temperature

Question 5

Which of the following describes the chloride ion exchange in red blood cells, where bicarbonate ions are exchanged for chloride ions to maintain electrical neutrality?

Accepted Answer

Chloride shift

Answer

Root effect

Answer

Bohr effect

Answer

Haldane effect

Question 6

A 45-year-old man undergoes spirometry testing. His results show FEV1 2.8 L (70% predicted), FVC 5.0 L (100% predicted), and FEV1/FVC ratio of 0.56. He has a 20-pack-year smoking history. What is the underlying pathophysiological mechanism for his reduced FEV1/FVC ratio?

Accepted Answer

Increased airway resistance from small airway obstruction and loss of elastic recoil

Answer

Reduced lung compliance from interstitial fibrosis

Answer

Bronchial smooth muscle hypertrophy without change in airway resistance

Answer

Decreased alveolar surface area from emphysematous destruction

Question 7

Surface tension of the fluid lining the alveoli increases during:

Accepted Answer

Expiration

Answer

Inspiration

Answer

Standing

Answer

Supine

Question 8

What is the effect of pulmonary embolism on the V/Q ratio in alveoli distal to the obstructed pulmonary artery?

Accepted Answer

Increased V/Q ratio approaching infinity (dead space)

Answer

Decreased V/Q ratio approaching zero

Answer

Normal V/Q ratio

Answer

Increased perfusion (Q) and decreased ventilation (V)

Question 9

Which of the following is correct about the flow volume curve shown below? (Recent NEET Pattern 2016-17)

Accepted Answer

A= Emphysema, B= Upper airway obstruction, C= Pulmonary fibrosis

Answer

A= Emphysema, B= Extraparenchymal restrictive lung disease, C= Pulmonary fibrosis

Answer

A= Extraparenchymal restrictive lung disease, B= upper airway obstruction, C= Pulmonary fibrosis

Answer

A= Emphysema, B= Upper airway obstruction, C= Extraparenchymal restrictive lung disease

Question 10

Which flow volume curve recording is shown below?

Accepted Answer

Variable extrathoracic obstruction

Answer

Parenchymal obstructive airway disease

Answer

Restrictive airway disease

Answer

Variable intrathoracic obstruction

Respiratory System — MCQs

Respiratory System — MCQs

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