Respiratory System Practice Questions

Q: What is the volume of air taken into the lungs during normal respiration called?

Tidal volume. **Explanation:** **Tidal Volume (TV)** is defined as the volume of air inspired or expired during a single cycle of normal, quiet respiration. In a healthy adult male, the average value is approximately **500 mL**. It represents the baseline ventilation required to maintain gas exchange under resting conditions. **Analysis of Incorrect Options:** * **Vital Capacity (VC):** This is the maximum volume of air a person can expel from the lungs after a maximum inhalation (VC = TV + IRV + ERV). It measures the total functional capacity of the lungs, not normal breathing. * **Timed Vital Capacity (FEV1):** This refers to the volume of air expired during the first second of a forced expiratory maneuver. It is a dynamic lung function test used clinically to differentiate between obstructive and restrictive lung diseases. * **Inspiratory Reserve Volume (IRV):** This is the additional volume of air that can be inspired over and above the normal tidal volume (approx. 2500–3000 mL). It represents the "reserve" used during deep breathing or exercise. **High-Yield Clinical Pearls for NEET-PG:** * **Anatomic Dead Space:** Out of the 500 mL of Tidal Volume, only about **350 mL** reaches the alveoli for gas exchange; the remaining **150 mL** remains in the conducting airways (Anatomic Dead Space). * **Minute Ventilation:** Calculated as $TV \times \text{Respiratory Rate}$ (approx. $500 \times 12 = 6000\text{ mL/min}$). * **Alveolar Ventilation:** A more accurate measure of gas exchange, calculated as $(TV - \text{Dead Space}) \times \text{Respiratory Rate}$. * In restrictive lung diseases (like pulmonary fibrosis), TV may remain normal or decrease, whereas in obstructive diseases (like asthma), the focus is usually on the reduction of FEV1.

Q: Which hormone accelerates surfactant production?

Glucocorticoids. **Explanation:** **Surfactant** is a surface-active lipoprotein complex (primarily Dipalmitoylphosphatidylcholine) secreted by **Type II Pneumocytes**. Its primary role is to reduce surface tension within the alveoli, preventing collapse during expiration. **Why Glucocorticoids are correct:** Glucocorticoids (Cortisol) are the most potent stimulators of surfactant synthesis. They act by accelerating the maturation of Type II pneumocytes and inducing the enzymes required for phospholipid synthesis. In clinical practice, if preterm delivery is anticipated (between 24–34 weeks), exogenous glucocorticoids like **Betamethasone or Dexamethasone** are administered to the mother to accelerate fetal lung maturity and prevent Respiratory Distress Syndrome (RDS). **Analysis of Incorrect Options:** * **Thyroxine (A):** While Thyroxine does play a minor synergistic role in lung maturation, it is not the primary hormone used clinically or physiologically for this specific acceleration compared to glucocorticoids. * **Carbamazepine (C):** This is an anticonvulsant medication used for epilepsy and trigeminal neuralgia; it has no physiological role in surfactant production. * **Iodine (D):** Iodine is essential for thyroid hormone synthesis but does not directly influence the pulmonary surfactant system. **High-Yield Clinical Pearls for NEET-PG:** * **Lecithin/Sphingomyelin (L/S) Ratio:** A ratio > 2:1 in amniotic fluid indicates fetal lung maturity. * **Inhibitors:** Insulin (maternal diabetes) and high doses of Oxygen can inhibit surfactant production or function. * **Composition:** The most abundant component is **Dipalmitoylphosphatidylcholine (DPPC)**. * **Surfactant Proteins:** SP-A and SP-D are involved in innate immunity, while SP-B and SP-C are crucial for the physical properties of the surfactant film.

Q: Which of the following is not a consequence of stimulation of lung C fiber endings?

Systemic vasoconstriction. **Explanation:** Lung C-fiber endings (Juxtacapillary or **J-receptors**) are sensory nerve endings located in the alveolar walls, near the pulmonary capillaries. They are innervated by the vagus nerve and are primarily stimulated by pulmonary congestion, edema, or chemical irritants (e.g., capsaicin). **Why Systemic Vasoconstriction is the Correct Answer:** Stimulation of J-receptors triggers the **J-reflex** (Pulmonary Chemoreflex). This reflex is characterized by a triad of **bradycardia, hypotension, and apnea**. The hypotension occurs due to **systemic vasodilation** (not vasoconstriction) and a decrease in heart rate. Therefore, systemic vasoconstriction is not a consequence of J-receptor stimulation. **Analysis of Incorrect Options:** * **Bronchoconstriction (A):** Stimulation of C-fibers leads to a reflex increase in parasympathetic outflow, causing narrowing of the airways. * **Apnea (B):** The immediate response to J-receptor activation is a brief period of apnea (cessation of breathing). * **Rapid Shallow Breathing (C):** Following the initial apnea, the respiratory pattern shifts to tachypnea (rapid) and shallow breathing to minimize the work of breathing in the presence of interstitial irritation. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** J-receptors are located in the alveolar interstitium, while bronchial C-fibers are in the bronchial walls. * **Classic Stimulus:** Pulmonary edema (interstitial fluid accumulation) is the most common physiological trigger. * **The Triad:** Remember the "Pulmonary Chemoreflex" triad: **Apnea, Bradycardia, and Hypotension.** * **Sensation:** J-receptor stimulation is believed to contribute to the sensation of **dyspnea** (shortness of breath) in patients with left heart failure.

Q: In the following diagram, the curve "X" represents the normal relationship of alveolar ventilation with PaCO2 when PaO2 is 100 mmHg. If pH changed from 7.4 to 7.3, by which curve will the change in alveolar ventilation shift?

Curve B. ***Curve B*** - A decrease in **pH from 7.4 to 7.3** represents **acidosis** (increased H+ ions), which stimulates the **respiratory center** and shifts the CO2 response curve **leftward/upward**. - This leftward shift means **greater alveolar ventilation** occurs at any given PaCO2 level, as the body compensates for acidosis by increasing ventilation to blow off CO2. *Curve A* - Represents a **rightward/downward shift**, which occurs during **alkalosis** (increased pH) when respiratory drive is **decreased**. - This would be inappropriate for acidosis, as it indicates **reduced ventilatory response** to CO2, opposite to what occurs with decreased pH. *Curve C* - Appears to represent either **no shift** from baseline or a different type of physiological change not related to **acid-base status**. - Does not account for the **increased respiratory drive** that occurs with acidosis and the need for compensatory hyperventilation. *Curve D* - Likely represents a **rightward shift** similar to alkalosis or potentially **hypoxia-related changes** in ventilatory response. - Fails to represent the **leftward shift** that characterizes the body's compensatory response to **metabolic acidosis** through increased alveolar ventilation.

Q: What is true regarding the alveolar-arterial oxygen gradient (A-a gradient)?

All of the above.. The **Alveolar-arterial (A-a) oxygen gradient** is a clinical measure used to differentiate between causes of hypoxemia. It represents the difference between the oxygen concentration in the alveoli ($P_AO_2$) and the arterial blood ($P_aO_2$). ### **Explanation of Options** * **Option A (Normal Gradient):** In a healthy young adult, the normal A-a gradient is typically **5–15 mmHg**. It increases naturally with age (estimated as $[Age/4] + 4$). A value of 15 mmHg is considered the upper limit of normal. * **Option B (Pulmonary Collapse):** Pulmonary collapse (atelectasis) leads to a **Right-to-Left Shunt**. Blood perfuses non-ventilated alveoli, entering the arterial system without being oxygenated. This significantly widens (increases) the A-a gradient. * **Option C (Venous Admixture):** This refers to the mixing of deoxygenated blood with oxygenated blood. Physiologically, this occurs via the **Thebesian veins** (draining the myocardium) and **bronchial veins**. This "physiological shunt" is the primary reason why a small A-a gradient exists even in healthy individuals. ### **High-Yield NEET-PG Pearls** 1. **Normal A-a Gradient Hypoxemia:** Occurs in **Alveolar Hypoventilation** (e.g., opioid overdose, neuromuscular weakness) and **High Altitude**. 2. **Increased A-a Gradient Hypoxemia:** Occurs in **V/Q Mismatch** (e.g., PE, pneumonia), **Diffusion defects** (e.g., ILD), and **Shunts** (e.g., Atelectasis, ASD/VSD). 3. **Formula:** $P_AO_2 = FiO_2(P_{atm} - P_{H2O}) - (P_aCO_2 / R)$. 4. **Key Distinction:** Hypoxemia due to shunting is the only type that **does not** fully correct with 100% supplemental oxygen.

Q: Under resting conditions, what is the total body oxygen consumption?

250 ml/min. **Explanation:** **1. Why Option D is Correct:** Under basal resting conditions, an average adult (70 kg) consumes approximately **250 ml of oxygen per minute ($VO_2$)**. This value represents the metabolic demand required to maintain vital organ functions. It is calculated using the **Fick Principle**, which states that oxygen consumption is the product of Cardiac Output ($CO$) and the Arterio-venous oxygen difference ($A-V O_2$ difference). * Calculation: $CO$ (5000 ml/min) × $[$Arterial $O_2$ (20 ml/dL) – Venous $O_2$ (15 ml/dL)$]$ = $5000 \times 0.05 = 250 \text{ ml/min}$. **2. Why Other Options are Incorrect:** * **Option A (100 ml/min):** This is significantly lower than the basal metabolic rate of a healthy adult. * **Option B (150 ml/min):** This value is insufficient for a 70 kg adult but may be seen in individuals with a very small body mass or severe hypometabolic states. * **Option C (200 ml/min):** While closer, the standard physiological reference for a resting adult is 250 ml/min. Carbon dioxide production ($VCO_2$) is approximately **200 ml/min**, which is often confused with $O_2$ consumption. **3. NEET-PG High-Yield Pearls:** * **Respiratory Quotient (RQ):** The ratio of $CO_2$ produced to $O_2$ consumed ($200/250$) is **0.8** on a mixed diet. * **MET (Metabolic Equivalent):** 1 MET is defined as $3.5 \text{ ml/kg/min}$ of $O_2$ consumption. For a 70 kg man: $70 \times 3.5 \approx 250 \text{ ml/min}$. * **Exercise:** During strenuous exercise, $O_2$ consumption can increase up to 20-fold (approx. 5000 ml/min) in elite athletes. * **Utilization Coefficient:** At rest, tissues extract about **25%** of the oxygen delivered by arterial blood.

Q: Which of the following is a typical manifestation of chronic hyperventilation?

Tetany. **Explanation:** The correct answer is **Tetany**. **Mechanism:** Chronic hyperventilation leads to excessive "washing out" of carbon dioxide ($CO_2$), resulting in **respiratory alkalosis**. In an alkaline state, the concentration of hydrogen ions ($H^+$) in the blood decreases. To compensate, $H^+$ ions dissociate from plasma proteins (like albumin). This frees up binding sites on albumin, which then bind to **ionized calcium ($Ca^{2+}$)**. Consequently, the level of free ionized calcium in the plasma drops (**hypocalcemia**), even though total body calcium remains normal. Since ionized calcium is crucial for stabilizing neuronal membranes, its deficiency increases membrane permeability to sodium, leading to nerve hyperexcitability and involuntary muscle contractions known as **tetany**. **Analysis of Incorrect Options:** * **A. Hypoxemia:** Hyperventilation actually increases alveolar $PO_2$ and typically results in normal or elevated arterial oxygen levels, not hypoxemia. * **B. Hyperphosphatemia:** Respiratory alkalosis causes an intracellular shift of phosphate to support increased glycolysis, typically leading to **hypophosphatemia**. * **D. Clubbing:** This is a sign of chronic hypoxia or underlying suppurative lung diseases (like bronchiectasis) and is not a physiological result of hyperventilation. **High-Yield Clinical Pearls for NEET-PG:** * **Trousseau’s sign** (carpal spasm with BP cuff inflation) and **Chvostek’s sign** (facial twitching) are classic bedside tests for latent tetany. * **Acute Management:** Breathing into a paper bag helps by increasing the fraction of inspired $CO_2$, reversing the alkalosis. * **Henderson-Hasselbalch Link:** Remember that $pH$ is inversely proportional to $pCO_2$. A decrease in $pCO_2$ always shifts the equation toward alkalemia.

Question 1

What is the volume of air taken into the lungs during normal respiration called?

Accepted Answer

Tidal volume

Answer

Vital capacity

Answer

Timed vital capacity

Answer

Inspiratory reserve volume

Question 2

Which hormone accelerates surfactant production?

Accepted Answer

Glucocorticoids

Answer

Thyroxine

Answer

Carbamazepine

Answer

Iodine

Question 3

Which of the following is not a consequence of stimulation of lung C fiber endings?

Accepted Answer

Systemic vasoconstriction

Answer

Bronchoconstriction

Answer

Apnea

Answer

Rapid shallow breathing

Question 4

What is the reason for the sigmoid shape of the hemoglobin-oxygen dissociation curve?

Accepted Answer

The binding of one oxygen molecule increases the affinity for the subsequent oxygen molecule.

Answer

The alpha chain has a higher affinity for oxygen than the beta chain.

Answer

The beta chain has a higher affinity for oxygen than the alpha chain.

Answer

Hemoglobin is acidic in nature.

Question 5

An anesthetized patient is mechanically ventilated at her normal tidal volume but at twice her normal frequency. When mechanical ventilation is stopped, the patient fails to breathe spontaneously for 1 minute. This temporary cessation of breathing occurs because:

Accepted Answer

The lowered arterial carbon dioxide tension (PaCO2) reduced central chemoreceptor activity.

Answer

The elevated arterial oxygen tension (PaO2) reduced peripheral chemoreceptor activity.

Answer

The elevated arterial oxygen tension (PaO2) reduced central chemoreceptor activity.

Answer

Low levels of nitrogen are known to inhibit ventilation.

Question 6

In the following diagram, the curve "X" represents the normal relationship of alveolar ventilation with PaCO2 when PaO2 is 100 mmHg. If pH changed from 7.4 to 7.3, by which curve will the change in alveolar ventilation shift?

Accepted Answer

Curve B

Answer

Curve A

Answer

Curve C

Answer

Curve D

Question 7

What is true regarding the alveolar-arterial oxygen gradient (A-a gradient)?

Accepted Answer

All of the above.

Answer

A normal gradient is approximately 15 mmHg (2 kPa).

Answer

An increased gradient can be caused by pulmonary collapse.

Answer

Venous admixture affects the A-a oxygen gradient.

Question 8

Under resting conditions, what is the total body oxygen consumption?

Accepted Answer

250 ml/min

Answer

100 ml/min

Answer

150 ml/min

Answer

200 ml/min

Question 9

Apneusis occurs when there is damage to:

Accepted Answer

The pneumotaxic center with bilateral vagotomy

Answer

The apneustic center with intact vagi

Answer

The apneustic center with bilateral vagotomy

Answer

The pneumotaxic center with intact vagi

Question 10

Which of the following is a typical manifestation of chronic hyperventilation?

Accepted Answer

Tetany

Answer

Hypoxemia

Answer

Hyperphosphatemia

Answer

Clubbing

Respiratory System — MCQs

Respiratory System — MCQs

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