Respiratory System Practice Questions

Q: Which hormone stimulates respiration?

Progesterone. **Explanation:** **Progesterone** is a potent respiratory stimulant. It acts through two primary mechanisms: 1. **Central Stimulation:** It increases the sensitivity of the respiratory center in the medulla to Carbon Dioxide ($CO_2$). 2. **Direct Action:** It acts as a direct stimulant to the respiratory drive, increasing tidal volume and minute ventilation. This physiological effect is most evident during the **luteal phase** of the menstrual cycle and during **pregnancy**, where elevated progesterone levels lead to chronic hyperventilation. This results in a physiological decrease in arterial $PCO_2$ (hypocapnia), creating a favorable $CO_2$ gradient for the fetus to excrete waste. **Analysis of Incorrect Options:** * **A. Estrogen:** While estrogen can enhance the effect of progesterone by increasing progesterone receptor expression, it does not independently stimulate respiration to a significant degree. * **C. Corticosteroids:** These primarily influence metabolic and anti-inflammatory pathways. While they are used to treat respiratory distress (e.g., asthma or fetal lung maturity), they do not act as physiological stimulants of the respiratory center. * **D. Prolactin:** This hormone is primarily involved in lactation and reproductive suppression; it has no documented role in stimulating the respiratory drive. **High-Yield Clinical Pearls for NEET-PG:** * **Pregnancy Physiology:** Pregnant women often experience "physiological dyspnea" due to progesterone-induced hyperventilation, leading to a state of **compensated respiratory alkalosis**. * **Therapeutic Use:** Medroxyprogesterone (a synthetic progestin) has been used clinically to treat **Obstructive Sleep Apnea (OSA)** and **Pickwickian Syndrome** (Obesity Hypoventilation Syndrome) due to its ventilatory stimulatory effects. * **Acid-Base Balance:** In pregnancy, the normal $PaCO_2$ drops to approximately **30–32 mmHg** (Normal: 40 mmHg).

Q: Pulmonary function tests show decreased FEV1, and an increased or normal FEV1/FVC ratio, along with decreased lung tissue compliance. Which condition is this characteristic of?

Restrictive lung disease. ### Explanation **1. Why Restrictive Lung Disease is Correct:** In **Restrictive Lung Disease (RLD)**, the primary pathology is the inability of the lungs to expand fully, often due to interstitial fibrosis or chest wall deformities. This leads to: * **Decreased Compliance:** The lung tissue becomes "stiff," requiring more pressure to inflate. * **Decreased FVC and FEV1:** Since total lung capacity is reduced, both the Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1) decrease. * **Normal or Increased FEV1/FVC Ratio:** Because the decrease in FVC is often more pronounced than or proportional to the decrease in FEV1, the ratio remains **>0.7 (or 70%)**. In some cases of fibrosis, increased radial traction on the airways keeps them open, actually increasing the ratio. **2. Why Other Options are Incorrect:** * **A, B, & C (Obstructive Diseases):** Bronchial asthma and Emphysema are types of **Obstructive Lung Diseases**. The hallmark of obstruction is increased airway resistance, leading to a **decreased FEV1/FVC ratio (<0.7)**. * **Emphysema (B):** Specifically shows **increased lung compliance** due to the destruction of elastic fibers (loss of elastic recoil), which is the opposite of the "stiff lung" described in the question. **3. NEET-PG High-Yield Pearls:** * **The Ratio Rule:** If FEV1/FVC is low = Obstructive. If FEV1/FVC is normal/high = Restrictive. * **Flow-Volume Loops:** Restrictive disease shows a "Witch’s Hat" appearance (narrow, tall loop shifted to the right). Obstructive disease shows a "Scooped-out" appearance. * **Compliance:** Compliance is inversely proportional to elastance ($C = 1/E$). In Fibrosis (Restrictive), elastance is high, so compliance is low.

Q: As compared to a 10-year-old child, a 1-year-old child will have higher?

Oxygen consumption. **Explanation:** The correct answer is **Oxygen consumption (VO2)**. **1. Why Oxygen Consumption is Higher:** In infants and young children, the metabolic rate is significantly higher compared to older children and adults. A 1-year-old child has a higher surface-area-to-body-mass ratio and rapidly growing tissues, leading to an oxygen consumption rate of approximately **6–8 mL/kg/min**. In contrast, a 10-year-old or an adult consumes about **3–4 mL/kg/min**. To meet this high metabolic demand, infants maintain a higher respiratory rate because their stroke volume (tidal volume) is limited by a compliant chest wall and immature alveoli. **2. Why Other Options are Incorrect:** * **B, C, and D (FRC, Tidal Volume, Vital Capacity):** These are all **lung volumes and capacities**. Lung volumes are directly proportional to body size and height. As a child grows from age 1 to 10, the lungs increase in size, the number of alveoli increases (alveolarization continues until age 8), and the chest wall becomes less compliant. Therefore, a 10-year-old will have significantly larger absolute values for FRC, Tidal Volume, and Vital Capacity than a 1-year-old. **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Rate:** Inversely proportional to age. (Infant: 30–40 bpm; Adult: 12–16 bpm). * **Closing Capacity:** In infants, the closing capacity is higher than the FRC, making them prone to early airway closure and atelectasis. * **Compliance:** Infants have high chest wall compliance (floppy ribs) but low lung compliance (less surfactant/small alveoli), leading to "retractions" during respiratory distress. * **Diaphragm:** The infant diaphragm has fewer Type I (slow-twitch, fatigue-resistant) muscle fibers, making them prone to respiratory muscle fatigue.

Q: Which of the following statements is true about physiological dead space?

It is often increased in lung disease.. **Explanation:** **Physiological dead space** refers to the total volume of the respiratory system that does not participate in gas exchange. It is the sum of **Anatomic dead space** (volume of conducting airways) and **Alveolar dead space** (alveoli that are ventilated but not perfused). **Why Option C is Correct:** In a healthy individual, physiological dead space is nearly equal to anatomic dead space because alveolar dead space is negligible. However, in **lung diseases** (such as COPD, pulmonary embolism, or fibrosis), there is a significant **Ventilation-Perfusion (V/Q) mismatch**. Alveoli may be ventilated but lack adequate blood flow, leading to a marked increase in alveolar dead space, and thus, an increase in total physiological dead space. **Analysis of Incorrect Options:** * **Option A:** Physiological dead space is measured using **Bohr’s Equation**, which utilizes **arterial PCO2** ($PaCO_2$) and expired PCO2 ($PeCO_2$), not PO2. * **Option B:** Physiological dead space is **equal to or greater** than anatomic dead space. It can never be smaller because it includes the anatomic dead space by definition. * **Option D:** This describes **Anatomic dead space**, which is determined by the structural geometry of the nose, pharynx, trachea, and bronchi. Physiological dead space is determined by both anatomy and functional V/Q status. **High-Yield Clinical Pearls for NEET-PG:** 1. **Bohr’s Equation:** $Vd/Vt = (PaCO_2 - PeCO_2) / PaCO_2$. Remember: "Physio is CO2." 2. **Anatomic Dead Space** is measured by **Fowler’s Method** (Nitrogen washout). 3. **Positioning:** Physiological dead space increases when standing (due to increased V/Q mismatch at the lung apex) compared to supine. 4. **Instrumental Dead Space:** Using a snorkel or ventilator tubing increases dead space, necessitating increased tidal volume to maintain alveolar ventilation.

Q: How is carbon dioxide transported in venous blood?

It is transported mainly in the form of bicarbonate.. **Explanation:** Carbon dioxide ($CO_2$) is transported in the blood via three primary mechanisms. The correct answer is **Option B** because the majority of $CO_2$ (**approximately 70%**) is transported in the form of **bicarbonate ions ($HCO_3^-$)**. 1. **Why Option B is correct:** When $CO_2$ enters the Red Blood Cells (RBCs), it reacts with water to form carbonic acid ($H_2CO_3$), catalyzed by the enzyme **carbonic anhydrase**. This acid dissociates into $H^+$ and $HCO_3^-$. The bicarbonate then exits the RBC into the plasma in exchange for chloride ions (the **Chloride Shift** or Hamburger phenomenon), where it serves as a major pH buffer. 2. **Why Option A is incorrect:** Only about **23%** of $CO_2$ is carried by hemoglobin as **carbaminohemoglobin**. Note that $CO_2$ binds to the amino groups of globin chains, not the heme iron. 3. **Why Option C is incorrect:** $CO_2$ is lipid-soluble and **crosses the blood-brain barrier (BBB) easily**. Once across, it reacts with water to form $H^+$, which is the primary stimulus for **central chemoreceptors** to regulate ventilation. 4. **Why Option D is incorrect:** While the statement itself is physiologically true (carbonic anhydrase does convert $CO_2$ to bicarbonate), it describes a *mechanism* of conversion rather than the *mode of transport* in venous blood. Option B directly answers "how" it is transported (the form it takes). **NEET-PG High-Yield Pearls:** * **Haldane Effect:** Deoxygenated hemoglobin has a higher affinity for $CO_2$ than oxygenated hemoglobin. This facilitates $CO_2$ loading in systemic tissues (venous blood). * **Dissolved Form:** About **7%** of $CO_2$ is transported physically dissolved in plasma (more soluble than $O_2$). * **Carbonic Anhydrase:** It is one of the fastest enzymes known; Type II is the predominant isoform in RBCs.

Q: Which of the following statements about the Ventilation/Perfusion (V/Q) ratio is true?

A V/Q ratio approaching infinity indicates no gas exchange.. The Ventilation/Perfusion (V/Q) ratio is a critical concept in respiratory physiology, representing the balance between air reaching the alveoli (V) and blood reaching the pulmonary capillaries (Q). ### **Explanation of the Correct Answer** **Option D** is correct because gas exchange requires both ventilation and perfusion. When the V/Q ratio approaches **infinity** (typically due to a total lack of perfusion, where Q = 0), the air in the alveoli cannot exchange gases with the blood. Similarly, when V/Q is **zero** (no ventilation), no fresh oxygen enters. Therefore, at either extreme of the V/Q spectrum, effective gas exchange ceases. ### **Analysis of Incorrect Options** * **Option A & B:** While physiologically true (obstruction leads to V/Q = 0; embolism leads to V/Q = ∞), these are **specific clinical scenarios** rather than universal physiological statements. In the context of this specific question's construction, Option D serves as the most fundamental physiological definition regarding gas exchange. * **Option C:** This is incorrect. A V/Q ratio of **zero** (V=0) indicates a **Shunt** (blood flows but isn't oxygenated). A V/Q ratio of **infinity** (Q=0) indicates **Dead Space** (ventilation occurs but no blood picks up oxygen). ### **High-Yield NEET-PG Pearls** * **Normal V/Q Ratio:** The average resting V/Q for the whole lung is approximately **0.8**. * **Regional Differences:** Both V and Q are higher at the **base** of the lung than the apex due to gravity. However, perfusion (Q) increases more significantly than ventilation (V) at the base. * **Apex vs. Base:** * **Apex:** Higher V/Q ratio (~3.3) → High $P_O2$, Low $P_CO2$. * **Base:** Lower V/Q ratio (~0.6) → Low $P_O2$, High $P_CO2$. * **Clinical Correlation:** *Mycobacterium tuberculosis* prefers the lung **apices** because the high V/Q ratio provides a high-oxygen environment.

Question 1

In a transection at the pontomedullary junction, respiration is maintained with slight irregularity. This is due to which structure?

Accepted Answer

Pre-Botzinger complex

Answer

Pneumotaxic centre

Answer

Apneustic Centre

Answer

Dorsal respiratory group

Question 2

Which hormone stimulates respiration?

Accepted Answer

Progesterone

Answer

Estrogen

Answer

Corticosteroids

Answer

Prolactin

Question 3

Which of the following factors is responsible for the pulmonary alveoli to be kept dry under normal circumstances?

Accepted Answer

Negative interstitial pressure

Answer

Macrophages

Answer

Tight junction between endothelium and alveolar surface

Answer

Pulmonary surfactant

Question 4

Pulmonary function tests show decreased FEV1, and an increased or normal FEV1/FVC ratio, along with decreased lung tissue compliance. Which condition is this characteristic of?

Accepted Answer

Restrictive lung disease

Answer

Obstructive lung disease

Answer

Emphysema

Answer

Bronchial asthma

Question 5

As compared to a 10-year-old child, a 1-year-old child will have higher?

Accepted Answer

Oxygen consumption

Answer

Functional residual capacity

Answer

Tidal volume

Answer

Vital capacity

Question 6

Which of the following statements is true about physiological dead space?

Accepted Answer

It is often increased in lung disease.

Answer

It is sometimes measured using the arterial PO2.

Answer

It is generally smaller than the anatomic dead space.

Answer

It is determined primarily by the geometry of the branching airways.

Question 7

Section of the vagus nerve results in what?

Accepted Answer

Increases in breath-holding time

Answer

Increased rate of respiration

Answer

Decreased depth of respiration

Answer

Irregular breathing patterns

Question 8

How is carbon dioxide transported in venous blood?

Accepted Answer

It is transported mainly in the form of bicarbonate.

Answer

It is carried mainly by hemoglobin.

Answer

It does not cross the blood-brain barrier.

Answer

It is converted to bicarbonate by carbonic anhydrase in red blood cells.

Question 9

Regarding the oxygen-hemoglobin dissociation curve, which statement is true?

Accepted Answer

Oxygen affinity will be equal in both HbF and HbA in the absence of 2,3-DPG.

Answer

The affinity of oxygen with hemoglobin decreases as hemoglobin attaches to oxygen in a linear fashion.

Answer

One hemoglobin molecule attaches to two molecules of 2,3-DPG.

Answer

Carboxyhemoglobin increases the release of oxygen in the blood, causing a rightward shift of the oxygen dissociation curve.

Question 10

Which of the following statements about the Ventilation/Perfusion (V/Q) ratio is true?

Accepted Answer

A V/Q ratio approaching infinity indicates no gas exchange.

Answer

In a complete airway obstruction, the V/Q ratio approaches zero.

Answer

In complete pulmonary embolism, the V/Q ratio approaches infinity.

Answer

A V/Q ratio of zero indicates dead space.

Respiratory System — MCQs

Respiratory System — MCQs

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