Respiratory System Practice Questions

Q: The approximate amount of air left in the lungs after maximal forced expiration in a normal woman is:

1.1 L. ### Explanation The volume of air remaining in the lungs after a maximal forced expiration is defined as the **Residual Volume (RV)**. This volume cannot be exhaled because the small airways collapse at low lung volumes, trapping air, and the chest wall reaches its inward limit of compression. **Why 1.1 L is correct:** In a healthy adult, the average Residual Volume is approximately **1.2 L in males** and **1.1 L in females**. Since the question specifically asks for the value in a **normal woman**, 1.1 L is the most accurate physiological estimate. **Analysis of Incorrect Options:** * **0.5 L (Option A):** This value corresponds to the **Tidal Volume (TV)**, which is the volume of air inspired or expired during a single normal breath. * **2.0 L (Option B) & 1.8 L (Option D):** These values are too high for RV. However, a value around 2.2–2.4 L would represent the **Functional Residual Capacity (FRC)**—the air remaining after a *normal* (passive) expiration (FRC = RV + ERV). **High-Yield NEET-PG Pearls:** 1. **Measurement:** Residual Volume **cannot** be measured by simple spirometry because the air never leaves the lungs. It must be measured using indirect methods: **Helium Dilution**, **Nitrogen Washout**, or **Body Plethysmography**. 2. **Clinical Correlation:** RV is significantly **increased** in obstructive lung diseases (e.g., Emphysema, Asthma) due to air trapping, leading to hyperinflation. 3. **Formula:** $FRC - ERV = RV$ (where ERV is Expiratory Reserve Volume). 4. **Aging:** RV typically increases with age as the elastic recoil of the lungs decreases.

Q: What is the normal vital capacity of the lungs?

4700 ml. **Explanation:** **Vital Capacity (VC)** is the maximum volume of air a person can exhale from the lungs after a maximum inhalation. It is a key indicator of pulmonary function and reflects the total "usable" gas exchange surface. **Why Option D is Correct:** The normal Vital Capacity in a healthy adult male is approximately **4600–4700 ml**. It is calculated by the sum of three primary lung volumes: * **Tidal Volume (TV):** 500 ml * **Inspiratory Reserve Volume (IRV):** 3000 ml * **Expiratory Reserve Volume (ERV):** 1100–1200 ml * **Calculation:** $500 + 3000 + 1200 = 4700 \text{ ml}$. **Analysis of Incorrect Options:** * **Option A (500 ml):** This represents the **Tidal Volume (TV)**, which is the volume of air inspired or expired during a normal, quiet breath. * **Option B (1200 ml):** This represents the **Residual Volume (RV)**—the air remaining in the lungs after forceful expiration—or the **Expiratory Reserve Volume (ERV)**. * **Option C (3000 ml):** This represents the **Inspiratory Reserve Volume (IRV)**, the additional volume that can be inspired above the normal tidal volume. **High-Yield NEET-PG Pearls:** 1. **VC vs. TLC:** Vital Capacity does *not* include Residual Volume. Total Lung Capacity (TLC) = VC + RV (approx. 5800–6000 ml). 2. **Clinical Significance:** VC is decreased in **Restrictive Lung Diseases** (e.g., Pulmonary Fibrosis, Kyphoscoliosis) but remains relatively normal or is only slightly reduced in obstructive diseases. 3. **Timed VC:** The most clinically significant measurement is **FEV1** (Forced Expiratory Volume in 1 second), which is normally 80% of the FVC (Forced Vital Capacity). 4. **Factors:** VC is higher in males, taller individuals, and athletes; it decreases with age and in the supine position.

Q: Respiratory distress syndrome is due to a defect in the biosynthesis of which substance?

Dipalmitoyl lecithin. ### Explanation **Correct Option: A. Dipalmitoyl lecithin** **Mechanism and Concept:** Respiratory Distress Syndrome (RDS), also known as Hyaline Membrane Disease, is primarily caused by a deficiency of **pulmonary surfactant**. Surfactant is a surface-active lipoprotein complex secreted by **Type II pneumocytes**. Its primary function is to reduce surface tension at the air-liquid interface of the alveoli, preventing alveolar collapse (atelectasis) during expiration. The most critical functional component of surfactant is **Dipalmitoylphosphatidylcholine (DPPC)**, commonly known as **Dipalmitoyl lecithin**. It accounts for approximately 50–60% of the surfactant composition. Chemically, it is a phospholipid with two palmitic acid chains. A defect in its biosynthesis or premature birth (before 34 weeks) leads to high surface tension, decreased lung compliance, and subsequent respiratory failure. **Why Other Options are Incorrect:** * **B, C, and D:** While Cephalin (Phosphatidylethanolamine), Serine (Phosphatidylserine), and Inositol (Phosphatidylinositol) are all phospholipids found in cell membranes and in minor quantities within surfactant, they do not possess the unique surface-tension-reducing properties of lecithin. They are not the primary functional molecules whose deficiency leads to RDS. **High-Yield Clinical Pearls for NEET-PG:** * **L/S Ratio:** Fetal lung maturity is assessed by the **Lecithin-Sphingomyelin ratio** in amniotic fluid. A ratio **> 2.0** indicates mature lungs. * **Glucocorticoids:** Antenatal administration of steroids (e.g., Betamethasone or Dexamethasone) accelerates surfactant synthesis by inducing enzymes in Type II pneumocytes. * **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 surfactant. * **Radiology:** RDS typically presents with a "ground-glass appearance" and air bronchograms on a chest X-ray.

Q: Carbon dioxide retention is seen in all, except?

Carbon monoxide poisoning. **Explanation:** The core concept here is the difference between **Type I** and **Type II respiratory failure**. Carbon dioxide retention (Hypercapnia) occurs when there is an issue with **ventilation** (the movement of air in and out of the lungs), whereas oxygenation issues can occur even when ventilation is preserved. **Why Carbon Monoxide (CO) Poisoning is the correct answer:** In CO poisoning, the primary pathology is **impaired oxygen transport**, not a failure of ventilation. CO binds to hemoglobin with 210 times the affinity of oxygen, causing a leftward shift of the oxygen-dissociation curve. However, the lungs' ability to exhale $CO_2$ remains intact. In fact, patients often hyperventilate due to tissue hypoxia, which leads to **decreased** $PaCO_2$ (hypocapnia) rather than retention. **Analysis of Incorrect Options:** * **Respiratory Failure:** Specifically Type II respiratory failure (Ventilatory failure) is defined by the inability to eliminate $CO_2$, leading to hypercapnia. * **Ventilator Failure:** Any mechanical failure or setting mismatch that reduces alveolar ventilation will directly result in $CO_2$ accumulation. * **Pulmonary Edema:** While initially causing Type I failure (hypoxia with low $CO_2$), severe or end-stage pulmonary edema leads to respiratory muscle fatigue and increased dead space, eventually resulting in $CO_2$ retention. **High-Yield Clinical Pearls for NEET-PG:** * **CO Poisoning Triad:** Cherry-red skin (rarely seen clinically), headache, and normal $SpO_2$ (pulse oximeters cannot distinguish between carboxyhemoglobin and oxyhemoglobin). * **Type I Respiratory Failure:** Hypoxia with normal/low $PaCO_2$ (e.g., Pneumonia, early Pulmonary Edema). * **Type II Respiratory Failure:** Hypoxia with high $PaCO_2$ (e.g., COPD, Neuromuscular weakness, Opioid overdose).

Q: Carbon monoxide poisoning causes which of the following types of hypoxia?

Anemic hypoxia. **Explanation:** **Why Anemic Hypoxia is Correct:** Anemic hypoxia occurs when the oxygen-carrying capacity of the blood is reduced, even though the partial pressure of arterial oxygen ($PaO_2$) remains normal. In Carbon Monoxide (CO) poisoning, CO binds to hemoglobin with an affinity **200–250 times greater** than oxygen, forming **carboxyhemoglobin**. This effectively reduces the amount of hemoglobin available to transport oxygen. Furthermore, CO causes a **leftward shift** of the oxygen-hemoglobin dissociation curve, meaning the remaining oxygen binds more tightly to hemoglobin and is not easily released to the tissues. **Why Other Options are Incorrect:** * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize oxygen despite adequate delivery (e.g., **Cyanide poisoning** inhibiting cytochrome oxidase). * **Anoxic (Hypoxic) Hypoxia:** Characterized by low arterial $PaO_2$ due to external factors like high altitude, airway obstruction, or alveolar hypoventilation. * **Stagnant (Ischemic) Hypoxia:** Occurs when blood flow to tissues is reduced despite normal oxygen content (e.g., heart failure, shock, or local embolism). **High-Yield Clinical Pearls for NEET-PG:** * **Pulse Oximetry:** Standard pulse oximeters cannot distinguish between oxyhemoglobin and carboxyhemoglobin, often giving **falsely normal** $SpO_2$ readings. * **Clinical Sign:** Patients may present with "cherry-red" skin discoloration (a classic but late sign). * **Treatment:** 100% Hyperbaric oxygen is the treatment of choice to displace CO from hemoglobin. * **Curve Shift:** CO poisoning is a classic cause of a **Left Shift** (along with Alkalosis, decreased 2,3-DPG, and Hypothermia).

Q: Which of the following has the maximum smooth muscle relative to its wall thickness?

Terminal bronchiole. **Explanation:** The correct answer is **Terminal bronchiole**. **1. Why Terminal Bronchiole is Correct:** In the respiratory tree, as we move from the trachea toward the alveoli, the amount of cartilage decreases while the relative proportion of smooth muscle increases. The **terminal bronchiole** marks the end of the conducting zone. It contains a complete layer of smooth muscle but lacks cartilage entirely. Because its wall is thin compared to larger bronchi, the smooth muscle constitutes the **maximum percentage of its total wall thickness**. This high muscle-to-wall ratio allows terminal bronchioles to significantly alter airway resistance through bronchoconstriction and bronchodilation. **2. Why Other Options are Incorrect:** * **Respiratory bronchiole:** These mark the beginning of the respiratory zone. Their walls are interrupted by occasional alveoli, leading to a fragmented and reduced smooth muscle layer compared to terminal bronchioles. * **Alveoli:** These are the primary sites of gas exchange. Their walls consist almost entirely of Type I and Type II pneumocytes and a basement membrane to facilitate diffusion; they **lack smooth muscle** entirely. * **Alveolar ducts:** These are passages lined with alveoli. While they contain small "knobs" of smooth muscle at the alveolar openings, the overall muscle content relative to the wall is significantly less than that of the terminal bronchiole. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Maximum Airway Resistance:** While terminal bronchioles have the most muscle, the **medium-sized bronchi** (generations 2-5) are the site of maximum airway resistance. * **Asthma Pathophysiology:** The abundance of smooth muscle in the bronchioles is the anatomical basis for bronchospasm in asthma. * **Anatomical Landmark:** The terminal bronchiole is the last structure supplied by the **bronchial circulation**; structures distal to it are supplied by the pulmonary circulation.

Q: An increase in which of the following parameters will shift the oxygen dissociation curve to the left?

Oxygen affinity of hemoglobin. **Explanation:** The Oxygen Dissociation Curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin ($SaO_2$). **Why the Correct Answer is Right:** A **Left Shift** indicates that hemoglobin has an **increased affinity for oxygen**. This means hemoglobin binds oxygen more tightly and is less willing to release it to the tissues. By definition, any factor that increases the oxygen affinity of hemoglobin will shift the curve to the left. At any given $PO_2$, the hemoglobin saturation will be higher than normal. **Why the Other Options are Wrong:** Options A, B, and C all cause a **Right Shift** (decreased affinity), which facilitates oxygen unloading to tissues (the Bohr Effect). * **A. Temperature:** Increased temperature (e.g., during fever or exercise) decreases affinity, shifting the curve to the right. * **B. Partial pressure of $CO_2$ ($PCO_2$):** Increased $CO_2$ leads to increased $H^+$ concentration (decreased pH). This stabilizes the "Tense" (T) state of hemoglobin, shifting the curve to the right. * **C. 2,3 DPG concentration:** This byproduct of glycolysis binds to the beta chains of hemoglobin, decreasing its affinity for $O_2$ and shifting the curve to the right. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Right Shift:** "**CADET**, face Right!" (**C**-$CO_2$, **A**-Acid/H+, **D**-2,3 DPG, **E**-Exercise, **T**-Temperature). * **Left Shift Causes:** Fetal Hemoglobin (HbF), Carbon Monoxide poisoning (COHb), Methemoglobinemia, and Alkalosis. * **$P_{50}$ Value:** The $PO_2$ at which hemoglobin is 50% saturated. A **Left Shift decreases $P_{50}$**, while a **Right Shift increases $P_{50}$**. Normal $P_{50}$ is approximately 26-27 mmHg.

Question 1

The approximate amount of air left in the lungs after maximal forced expiration in a normal woman is:

Accepted Answer

1.1 L

Answer

0.5 L

Answer

2.0 L

Answer

1.8 L

Question 2

What is the normal vital capacity of the lungs?

Accepted Answer

4700 ml

Answer

500 ml

Answer

1200 ml

Answer

3000 ml

Question 3

Respiratory distress syndrome is due to a defect in the biosynthesis of which substance?

Accepted Answer

Dipalmitoyl lecithin

Answer

Dipalmitoyl cephalin

Answer

Dipalmitoyl serine

Answer

Dipalmitoyl inositol

Question 4

Respiration stops in the last stage of expiration, during forced expiration, because of:

Accepted Answer

Dynamic compression of airways

Answer

Respiratory muscle fatigue

Answer

Collapse of alveoli

Answer

Breaking effect of inspiratory muscles

Question 5

Carbon dioxide retention is seen in all, except?

Accepted Answer

Carbon monoxide poisoning

Answer

Respiratory failure

Answer

Ventilator failure

Answer

Pulmonary edema

Question 6

Carbon monoxide poisoning causes which of the following types of hypoxia?

Accepted Answer

Anemic hypoxia

Answer

Histotoxic hypoxia

Answer

Anoxic hypoxia

Answer

Stagnant hypoxia

Question 7

In hyperventilation, what happens to the P50 and Hb affinity for O2?

Accepted Answer

P50 increases and affinity O2 decreases

Answer

P50 and Hb affinity for O2 increases

Answer

P50 and Hb affinity for O2 decreases

Answer

P50 decreases and affinity O2 increases

Question 8

Which of the following has the maximum smooth muscle relative to its wall thickness?

Accepted Answer

Terminal bronchiole

Answer

Respiratory bronchiole

Answer

Alveoli

Answer

Alveolar ducts

Question 9

Which of the following statements regarding the vascularity of the lungs is TRUE?

Accepted Answer

Pulmonary blood flow is less in the upper parts of the lungs compared to the lower parts

Answer

Hypoxia causes pulmonary vasodilation

Answer

The ratio of pulmonary to systemic vascular resistance is usually greater than 0.3

Answer

Pulmonary perfusion is greater in the apical lobe than in the base

Question 10

An increase in which of the following parameters will shift the oxygen dissociation curve to the left?

Accepted Answer

Oxygen affinity of hemoglobin

Answer

Temperature

Answer

Partial pressure of CO2

Answer

2,3 DPG concentration

Respiratory System — MCQs

Respiratory System — MCQs

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