Respiratory System Practice Questions

Q: The surfactant is produced by which of the following cells?

Type II Pneumocytes. **Explanation:** The correct answer is **Type II Pneumocytes**. **1. Why Type II Pneumocytes are correct:** Type II pneumocytes (granular pneumocytes) are cuboidal cells located in the alveolar walls, covering about 5% of the alveolar surface area. Their primary function is the synthesis, storage, and secretion of **pulmonary surfactant**, a lipoprotein complex (mainly Dipalmitoylphosphatidylcholine - DPPC). Surfactant reduces surface tension at the air-liquid interface, preventing alveolar collapse (atelectasis) during expiration and increasing lung compliance. These cells also act as "progenitor cells"; they can proliferate and differentiate into Type I pneumocytes following lung injury. **2. Why the other options are incorrect:** * **Type I Pneumocytes:** These are thin, squamous cells covering 95% of the alveolar surface. Their primary role is facilitating gas exchange due to their minimal thickness. They do not produce surfactant. * **Alveolar Macrophages (Dust Cells):** These are immune cells that phagocytose debris, dust, and pathogens within the alveoli. * **Clara Cells (Club Cells):** Found in the bronchioles, these cells secrete a surfactant-like substance (surface-active agent) and uteroglobin, but they are not the primary source of pulmonary alveolar surfactant. **High-Yield Clinical Pearls for NEET-PG:** * **Lamellar Bodies:** Surfactant is stored in these characteristic intracellular organelles within Type II pneumocytes. * **Development:** Surfactant production begins between **24–28 weeks** of gestation, but adequate levels are usually reached only after **35 weeks**. * **L/S Ratio:** A Lecithin/Sphingomyelin ratio of **>2** in amniotic fluid indicates fetal lung maturity. * **NRDS:** Deficiency of surfactant in premature infants leads to Neonatal Respiratory Distress Syndrome (Hyaline Membrane Disease).

Q: A 54-year-old man sustains third degree burns in a house fire. His respiratory rate is 30/min, Hb = 17 g/dL, arterial PO2 is 95 mm Hg, and arterial O2 saturation is 50%. What is the most likely cause of his low oxygen saturation?

Carbon monoxide poisoning. ### Explanation **Correct Option: B. Carbon Monoxide (CO) Poisoning** The hallmark of carbon monoxide poisoning is a **normal arterial $PO_2$** (dissolved oxygen) but a **critically low arterial $O_2$ saturation ($SaO_2$)**. * **Mechanism:** CO has an affinity for hemoglobin that is 200–250 times greater than oxygen. It binds to hemoglobin to form **carboxyhemoglobin**, physically displacing oxygen and reducing the $SaO_2$. * **The "Normal $PO_2$" Trap:** $PO_2$ measures oxygen dissolved in plasma, which is unaffected by CO. Therefore, the patient is not technically "hypoxemic" in terms of $PO_2$, but suffers from severe **anemic hypoxia** because the oxygen-carrying capacity is decimated. * **Left Shift:** CO also causes a leftward shift of the Oxyhemoglobin Dissociation Curve (OHDC), making it harder for the remaining oxygen to be released to tissues. **Why Incorrect Options are Wrong:** * **A & C (Airway Obstruction/Pulmonary Edema):** Both conditions interfere with gas exchange at the alveolar-capillary membrane. This would lead to a **low arterial $PO_2$** (hypoxemia), which is not present in this patient ($PO_2$ = 95 mmHg is normal). * **D (Fever):** Fever causes a **Right shift** of the OHDC (decreasing affinity), but it does not cause a massive drop in $SaO_2$ to 50% in the presence of normal $PO_2$. **NEET-PG High-Yield Pearls:** 1. **Pulse Oximetry Gap:** Standard pulse oximeters cannot distinguish between oxyhemoglobin and carboxyhemoglobin; they may show a falsely normal $SaO_2$. Co-oximetry is required for diagnosis. 2. **Cherry Red Skin:** A classic but rare clinical sign of CO poisoning. 3. **Treatment:** 100% Hyperbaric Oxygen (HBO) to reduce the half-life of carboxyhemoglobin. 4. **OHDC Shift:** CO poisoning causes a **Left shift**; Anemia (low Hb) does not shift the curve, but CO poisoning (functional anemia) does.

Q: Which of the following findings demonstrates a difference between pulmonary circulation and systemic circulation?

Pulmonary vasoconstriction in response to hypoxia. **Explanation:** The fundamental difference between pulmonary and systemic circulation lies in their response to low oxygen levels (hypoxia). **1. Why Option B is Correct:** In the **systemic circulation**, hypoxia causes **vasodilation** to increase blood flow and oxygen delivery to tissues. However, in the **pulmonary circulation**, hypoxia triggers **Hypoxic Pulmonary Vasoconstriction (HPV)**. This is a protective mechanism where pulmonary arterioles constrict in poorly ventilated areas of the lung. This shunts blood away from hypoxic alveoli toward well-ventilated alveoli, optimizing **ventilation-perfusion (V/Q) matching** and preventing arterial hypoxemia. **2. Why the other options are incorrect:** * **Option A:** This is the opposite of the physiological reality in the lungs; vasodilation in response to hypoxia occurs in systemic vessels (e.g., skeletal muscle), not pulmonary ones. * **Option C:** Blood volume changes during the cardiac cycle do not define the functional difference between these two circuits in the context of vascular regulation. * **Option D:** The pulmonary circulation is a **low-pressure, low-resistance** system with very little basal vasoconstrictor tone compared to the systemic circulation, which maintains high tone to regulate blood pressure. **High-Yield NEET-PG Pearls:** * **Mechanism of HPV:** Hypoxia inhibits voltage-gated potassium channels in pulmonary artery smooth muscle cells, leading to depolarization and calcium influx, causing contraction. * **Clinical Correlation:** Global alveolar hypoxia (e.g., at high altitudes) causes generalized pulmonary vasoconstriction, leading to **High Altitude Pulmonary Edema (HAPE)** and pulmonary hypertension. * **V/Q Ratio:** The main goal of HPV is to minimize "shunting" by ensuring blood only goes where oxygen is available.

Q: Diffusion of oxygen at the tissue level is affected in all the following poisoning except?

Curare. This question tests the understanding of the **Oxygen Cascade** and the specific mechanisms by which toxins interfere with oxygen delivery and utilization. ### **Explanation** The correct answer is **Curare (B)**. Curare is a non-depolarizing neuromuscular blocking agent that acts at the nicotinic receptors of the motor endplate [2]. It causes **respiratory failure** by paralyzing the diaphragm and intercostal muscles. However, it does **not** interfere with the biochemical or physical diffusion of oxygen at the tissue level; if the patient is mechanically ventilated, oxygen diffusion remains perfectly normal. ### **Why the other options are incorrect:** * **Carbon Monoxide (A):** CO binds to hemoglobin with 200x higher affinity than $O_2$, forming Carboxyhemoglobin. It causes a **leftward shift** of the oxygen-dissociation curve, preventing the release (diffusion) of $O_2$ from hemoglobin to the tissues [1]. * **Phosgene (C):** This is a pulmonary irritant that causes severe **alveolar-capillary membrane damage** and non-cardiogenic pulmonary edema. This physical barrier and the destruction of the membrane directly impair the diffusion of gases. * **Cyanides (D):** Cyanide inhibits **Cytochrome Oxidase $a_3$** in the electron transport chain. This prevents the tissues from utilizing oxygen (histotoxic hypoxia). While $O_2$ is present in the blood, the concentration gradient for diffusion is abolished because the cellular "sink" for oxygen is blocked. ### **NEET-PG High-Yield Pearls** * **Cyanide Poisoning:** Characterized by a narrow arterial-venous $O_2$ difference (venous blood remains bright red). Antidote: Nitrites + Sodium Thiosulfate or Hydroxocobalamin. * **CO Poisoning:** "Cherry red" skin discoloration (post-mortem). Treatment: 100% Hyperbaric Oxygen. * **Curare Antidote:** Neostigmine (acetylcholinesterase inhibitor) combined with Glycopyrrolate.

Q: The provided pressure-volume curves represent a normal subject and a patient with a pulmonary disease. Based on these curves, what is the likely pulmonary condition of the patient?

Emphysema. ***Emphysema*** - **Increased lung compliance** causes the pressure-volume curve to shift **left and upward**, allowing greater volume at lower pressures due to **alveolar wall destruction**. - Loss of **elastic recoil** from damaged alveolar septa results in easier lung expansion but impaired expiration. *Pulmonary fibrosis* - **Decreased lung compliance** shifts the pressure-volume curve **right and downward**, requiring higher pressures to achieve the same volume. - **Collagen deposition** and **fibrotic tissue** make the lungs stiffer and harder to expand, opposite to the pattern seen in emphysema. *Asbestosis* - A **restrictive lung disease** that decreases compliance, shifting the curve **right and downward** like other fibrotic conditions. - **Asbestos fiber deposition** causes **pulmonary fibrosis** and scarring, making lungs less distensible, not more compliant. *Pulmonary congestion* - **Fluid accumulation** in pulmonary interstitium and alveoli decreases compliance, shifting the curve **right and downward**. - **Increased pulmonary capillary pressure** from heart failure causes **interstitial edema**, making lungs stiffer and harder to ventilate.

Q: CO2 retention is seen in which of the following conditions?

Respiratory failure. **Explanation:** **1. Why Respiratory Failure is correct:** Carbon dioxide (CO2) retention, or **hypercapnia**, occurs when alveolar ventilation is inadequate to remove the CO2 produced by metabolism. In **Type II Respiratory Failure** (Ventilatory Failure), there is a primary failure of the "pump" (respiratory muscles, chest wall, or central drive), leading to reduced minute ventilation. This results in the hallmark clinical finding of **hypoxemia with hypercapnia (PaCO2 >45 mmHg).** **2. Why other options are incorrect:** * **Carbon Monoxide (CO) Poisoning:** CO binds to hemoglobin with an affinity 200–250 times greater than oxygen, causing a leftward shift of the oxygen-dissociation curve. While it causes severe tissue hypoxia, the ventilation drive usually remains intact or increases, meaning CO2 levels are typically **normal or decreased** (due to compensatory hyperventilation). * **High Altitude:** At high altitudes, the low barometric pressure leads to hypoxia. This stimulates peripheral chemoreceptors, causing **hyperventilation**. Increased breathing "washes out" CO2, leading to **hypocapnia** and respiratory alkalosis, not retention. **3. High-Yield Clinical Pearls for NEET-PG:** * **Type I Respiratory Failure:** Hypoxemia with normal/low PaCO2 (e.g., Pneumonia, Pulmonary Edema). * **Type II Respiratory Failure:** Hypoxemia with high PaCO2 (e.g., COPD, Myasthenia Gravis, Opioid overdose). * **CO2 Narcosis:** High levels of PaCO2 (>70–80 mmHg) can cause confusion, tremors, and eventually coma. * **Haldane Effect:** Deoxygenated hemoglobin has a higher affinity for CO2; this helps in CO2 loading at tissues and unloading at lungs.

Q: Severe pulmonary congestion and edema is seen when PCWP rises above which value?

25 mm Hg. **Explanation:** The correct answer is **25 mm Hg**. **1. Underlying Medical Concept:** Pulmonary Capillary Wedge Pressure (PCWP) is an indirect estimate of left atrial pressure. Under normal physiological conditions, the **Colloid Osmotic Pressure (Oncotic Pressure)** of the plasma is approximately **25–28 mm Hg**. This pressure acts to keep fluid inside the pulmonary capillaries. As long as the PCWP (hydrostatic pressure) remains below the plasma oncotic pressure, fluid filtration into the interstitium is minimal and easily cleared by lymphatics. When PCWP exceeds **25 mm Hg**, the hydrostatic pressure overcomes the oncotic pressure, causing a massive shift of fluid into the alveoli, resulting in **severe pulmonary edema**. **2. Analysis of Incorrect Options:** * **A (5 mm Hg):** This is within the normal range of PCWP (typically 5–12 mm Hg). At this level, the lungs remain "dry." * **B (10 mm Hg):** This is still within the normal physiological range and does not cause congestion. * **C (15 mm Hg):** While this represents mild elevation (seen in early heart failure), the lymphatic system can usually compensate for the slight increase in fluid transudation. Clinical congestion may begin, but "severe edema" does not occur until the oncotic threshold is breached. **3. NEET-PG High-Yield Pearls:** * **Normal PCWP:** 5–12 mm Hg. * **Cephalization (Antler Sign):** Seen on X-ray when PCWP is 12–18 mm Hg. * **Kerley B Lines:** Seen when PCWP is 18–25 mm Hg (interstitial edema). * **Bat-wing Opacity:** Seen when PCWP >25 mm Hg (alveolar edema). * **Gold Standard:** PCWP is measured using a **Swan-Ganz catheter** (Pulmonary Artery Catheterization).

Question 1

Moderate exercise is one of the most powerful stimulators of ventilation. By what mechanism does this occur?

Accepted Answer

None of the above

Answer

Low partial pressure of oxygen in inspired air

Answer

Low partial pressure of oxygen in mixed venous blood

Answer

Low pH in inspired air

Question 2

The surfactant is produced by which of the following cells?

Accepted Answer

Type II Pneumocytes

Answer

Type I Pneumocytes

Answer

Alveolar macrophages

Answer

Clara cells

Question 3

A 54-year-old man sustains third degree burns in a house fire. His respiratory rate is 30/min, Hb = 17 g/dL, arterial PO2 is 95 mm Hg, and arterial O2 saturation is 50%. What is the most likely cause of his low oxygen saturation?

Accepted Answer

Carbon monoxide poisoning

Answer

Airway obstruction from smoke inhalation

Answer

Pulmonary edema

Answer

Fever

Question 4

What is the respiratory quotient of protein in the body?

Accepted Answer

0.8

Answer

0.5

Answer

0.75

Answer

1

Question 5

Which of the following findings demonstrates a difference between pulmonary circulation and systemic circulation?

Accepted Answer

Pulmonary vasoconstriction in response to hypoxia

Answer

Pulmonary vasodilation in response to hypoxia

Answer

Decreased blood volume during systole

Answer

Increased basal vasoconstrictor tone

Question 6

Diffusion of oxygen at the tissue level is affected in all the following poisoning except?

Accepted Answer

Curare

Answer

Carbon monoxide

Answer

Phosgene

Answer

Cyanides

Question 7

The provided pressure-volume curves represent a normal subject and a patient with a pulmonary disease. Based on these curves, what is the likely pulmonary condition of the patient?

Accepted Answer

Emphysema

Answer

Pulmonary fibrosis

Answer

Asbestosis

Answer

Pulmonary congestion

Question 8

CO2 retention is seen in which of the following conditions?

Accepted Answer

Respiratory failure

Answer

Carbon monoxide poisoning

Answer

High altitude

Answer

All of the above

Question 9

Closing volume is the volume of lung

Accepted Answer

Above residual volume in dependent part of lung

Answer

Above residual volume in the non-dependent part of lung

Answer

Above tidal volume in non-dependent part of lung

Answer

Above tidal volume in dependent part of lung

Question 10

Severe pulmonary congestion and edema is seen when PCWP rises above which value?

Accepted Answer

25 mm Hg

Answer

5 mm Hg

Answer

10 mm Hg

Answer

15 mm Hg

Respiratory System — MCQs

Respiratory System — MCQs

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