Respiratory System Practice Questions

Q: Which of the following conditions does not promote the dissociation of O2 from hemoglobin?

Increase in the partial pressure of O2. ### Explanation The dissociation of oxygen from hemoglobin is represented by the **Oxygen-Dissociation Curve (ODC)**. A shift to the **right** indicates decreased affinity (increased dissociation/unloading to tissues), while a shift to the **left** indicates increased affinity (decreased dissociation/loading in lungs). **Why Option D is Correct:** An **increase in the partial pressure of O2 ($PO_2$)** occurs in the pulmonary capillaries. According to the law of mass action and the cooperative binding property of hemoglobin, high $PO_2$ promotes the binding of oxygen to heme groups, stabilizing the **R (Relaxed) state**. This promotes the formation of oxyhemoglobin rather than dissociation. **Why the Other Options are Incorrect:** Options A, B, and C all cause a **Right Shift** in the ODC, promoting oxygen unloading (dissociation) via the stabilization of the **T (Tense) state**: * **Decrease in pH (Acidosis) & Increase in $CO_2$:** Known as the **Bohr Effect**. High $H^+$ and $CO_2$ (metabolic byproducts in tissues) reduce Hb's affinity for $O_2$. * **Increase in 2,3-DPG:** This glycolytic intermediate binds to the central cavity of the deoxyhemoglobin tetramer, stabilizing the T-state and pushing $O_2$ off the heme. --- ### High-Yield Clinical Pearls for NEET-PG * **Mnemonic for Right Shift (CADET, face Right!):** **C**O2 increase, **A**cidosis, **D**PG (2,3-DPG) increase, **E**xercise, **T**emperature increase. * **Fetal Hemoglobin (HbF):** Has a **Left Shift** compared to HbA because it has a lower affinity for 2,3-DPG, allowing it to "pull" oxygen from maternal blood. * **Carbon Monoxide (CO) Poisoning:** Causes a **Left Shift** of the remaining heme sites (increasing their affinity and preventing $O_2$ release to tissues) while simultaneously decreasing the total $O_2$ carrying capacity.

Q: Carbon monoxide poisoning is a type of which of the following?

Anemic hypoxia. **Explanation:** **Why Anemic Hypoxia is Correct:** Anemic hypoxia is defined as a condition where the arterial $PO_2$ is normal, but the **oxygen-carrying capacity** of the blood is reduced. In Carbon Monoxide (CO) poisoning, CO binds to hemoglobin with an affinity approximately **210–250 times greater** than oxygen, forming carboxyhemoglobin. This reduces the amount of hemoglobin available to carry 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. Despite normal dissolved oxygen (normal $PaO_2$), the total oxygen content is severely decreased, fitting the definition of anemic hypoxia. **Why Other Options are Incorrect:** * **Hypoxic Hypoxia:** Characterized by low arterial $PO_2$. This occurs at high altitudes or in pulmonary diseases where oxygen cannot enter the blood. In CO poisoning, $PaO_2$ remains normal. * **Stagnant (Ischemic) Hypoxia:** Occurs due to slow circulation or reduced blood flow (e.g., heart failure, shock). The blood has oxygen, but it isn't reaching tissues fast enough. * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize oxygen despite adequate delivery (e.g., **Cyanide poisoning**, which inhibits Cytochrome Oxidase). **High-Yield Clinical Pearls for NEET-PG:** * **Cherry-red skin discoloration** is a classic (though often post-mortem) sign of CO poisoning. * **Pulse Oximetry (SpO2)** is notoriously unreliable in CO poisoning because standard sensors cannot distinguish between oxyhemoglobin and carboxyhemoglobin, often giving falsely high readings. * **Treatment:** 100% Oxygen (reduces CO half-life from 5 hours to ~80 mins) or Hyperbaric Oxygen.

Q: Which of the following statements about surfactant is false?

Consists of 3 types of unique proteins in it.. **Explanation** The correct answer is **D** because surfactant actually contains **four** unique proteins, not three. These are designated as **SP-A, SP-B, SP-C, and SP-D**. * **SP-A and SP-D** are hydrophilic and play a major role in innate immunity (opsonization of pathogens). * **SP-B and SP-C** are hydrophobic and are essential for the spreading and stability of the surfactant film. **Analysis of other options:** * **Option A:** Surfactant is synthesized, stored (in lamellar bodies), and secreted by **Type II pneumocytes**, which cover about 5% of the alveolar surface area. * **Option B:** Surfactant is approximately 90% lipids and 10% proteins. The most abundant phospholipid is **DPPC** (Lecithin), which is primarily responsible for reducing surface tension. **Phosphatidylglycerol (PG)** is the second most common lipid and serves as a marker for fetal lung maturity. * **Option C:** By definition, surfactant is a surface-active agent. It reduces the work of breathing by lowering alveolar surface tension, preventing alveolar collapse (atelectasis) at low lung volumes. **High-Yield Clinical Pearls for NEET-PG:** * **Law of Laplace:** $P = 2T/r$. Surfactant reduces tension ($T$), preventing small alveoli from collapsing into larger ones. * **Fetal Lung Maturity:** Surfactant production begins at 24–28 weeks, but matures significantly after **35 weeks**. * **L/S Ratio:** A Lecithin/Sphingomyelin ratio **> 2.0** in amniotic fluid indicates mature lungs. * **Glucocorticoids:** Administered to mothers in preterm labor to accelerate surfactant production by stimulating Type II cells.

Q: What is the normal pulmonary artery pressure?

25/8 mm Hg. ### Explanation **1. Understanding the Correct Answer (Option C: 25/8 mm Hg)** The pulmonary circulation is a **low-pressure, low-resistance system** compared to the systemic circulation. The right ventricle (RV) only needs to pump blood through the lungs to the left atrium. * **Systolic Pulmonary Artery Pressure (sPAP):** Normally ranges from **15–25 mm Hg**. This reflects the pressure during RV contraction. * **Diastolic Pulmonary Artery Pressure (dPAP):** Normally ranges from **8–15 mm Hg**. This reflects the pressure while the pulmonary valve is closed. * **Mean Pulmonary Artery Pressure (mPAP):** Typically **15 mm Hg**. A mPAP >20 mm Hg at rest is the diagnostic threshold for Pulmonary Hypertension. **2. Analysis of Incorrect Options** * **Option A (120/80 mm Hg):** This represents normal **Systemic Arterial Pressure**. The left ventricle must generate significantly higher pressure to overcome high systemic vascular resistance and perfuse the entire body. * **Option B (25/0 mm Hg):** This represents **Right Ventricular (RV) Pressure**. While the systolic pressure matches the pulmonary artery, the diastolic pressure in the ventricle drops to near zero as it relaxes to fill with blood. * **Option C (120/0 mm Hg):** This represents **Left Ventricular (LV) Pressure**. The LV reaches high systolic pressures but, like the RV, its diastolic pressure drops to near zero to allow for filling. **3. High-Yield Clinical Pearls for NEET-PG** * **PCWP (Pulmonary Capillary Wedge Pressure):** Normal is **6–12 mm Hg**. It is a clinical proxy for Left Atrial Pressure. * **West Zones of the Lung:** Blood flow distribution is determined by the relationship between Alveolar pressure (PA), Arterial pressure (Pa), and Venous pressure (Pv). * **Hypoxic Pulmonary Vasoconstriction:** Unlike systemic vessels (which dilate), pulmonary arterioles **constrict** in response to low alveolar oxygen to shunt blood to better-ventilated areas.

Q: What is the immediate response of J receptor stimulation?

Apnea. **Explanation:** **J receptors (Juxtacapillary receptors)** are sensory nerve endings located in the alveolar walls, in close proximity to the pulmonary capillaries. They are innervated by **unmyelinated C-fibers** of the vagus nerve. **Why Apnea is the Correct Answer:** The classic response to J receptor stimulation is known as the **"Pulmonary Chemoreflex."** When these receptors are stimulated—typically by pulmonary edema, congestion, pneumonia, or chemical irritants (like capsaicin)—they trigger a rapid reflex triad. The **immediate** respiratory response is a brief period of **Apnea** (cessation of breathing), which is then followed by rapid, shallow breathing (tachypnea). **Analysis of Incorrect Options:** * **Tachycardia & Hypertension (A & B):** J receptor stimulation actually produces the opposite effect. It triggers a parasympathetic response leading to **Bradycardia** (decreased heart rate) and **Hypotension** (decreased blood pressure). * **Tachypnea (C):** While tachypnea does occur, it is the *secondary* or delayed response. The question asks for the *immediate* response, which is the transient apnea. **High-Yield Clinical Pearls for NEET-PG:** * **Stimulus:** The most common physiological stimulus is **interstitial fluid volume expansion** (e.g., Left Heart Failure leading to pulmonary edema). * **The Triad:** Remember the J-reflex triad: **Apnea, Bradycardia, and Hypotension.** * **Sensation of Dyspnea:** J receptor activation is a major contributor to the feeling of "shortness of breath" in patients with pulmonary congestion. * **Location:** They are located in the alveolar interstitium, unlike Irritant Receptors (found in the epithelium of the upper airways).

Q: Conducting zone of the respiratory system is defined as:

0th generation to 16th generation of airways. ### Explanation The respiratory system is divided into two functional zones based on the **Weibel Model** of airway branching, which describes 23 generations of airways. **1. Why Option B is Correct:** The **Conducting Zone** extends from the **trachea (0th generation)** to the **terminal bronchioles (16th generation)**. Its primary functions are to warm, humidify, and filter inspired air and distribute it to the gas-exchange surfaces. Crucially, this zone contains no alveoli; therefore, no gas exchange occurs here. This volume of air is known as the **Anatomical Dead Space** (approximately 150 mL). **2. Why the Other Options are Incorrect:** * **Option A:** The 1st generation refers specifically to the mainstem bronchi. The conducting zone begins at the trachea (0th). * **Option C:** This describes the **entire respiratory tree** (0 to 23). It conflates the conducting zone with the respiratory zone. * **Option D:** This describes the **Respiratory Zone**, which starts from the **respiratory bronchioles (17th generation)** and ends at the **alveolar sacs (23rd generation)**. This is where gas exchange actually takes place. **High-Yield Facts for NEET-PG:** * **Cartilage:** Present up to the 10th generation (bronchi); absent in bronchioles (11th generation onwards). * **Cilia:** Present up to the respiratory bronchioles, but disappear before the alveolar ducts. * **Smooth Muscle:** Highest relative amount is found in the **terminal bronchioles** (the last part of the conducting zone). * **Velocity of Airflow:** It is highest in the trachea and **lowest in the respiratory zone** due to the massive increase in total cross-sectional area, allowing time for diffusion.

Q: Which of the following statements is true regarding asthma?

Increased FRC and increased residual volume. **Explanation:** Asthma is a chronic inflammatory **obstructive lung disease** characterized by reversible airway narrowing. The pathophysiology revolves around **air trapping** and **hyperinflation**. **1. Why Option B is Correct:** During an asthma attack, bronchoconstriction and mucus plugging lead to premature closure of the small airways during expiration. This prevents the lungs from emptying completely, a phenomenon known as **air trapping**. * **Residual Volume (RV):** The volume of air remaining in the lungs after maximal expiration increases because air is trapped behind closed airways. * **Functional Residual Capacity (FRC):** Since FRC is the sum of RV and Expiratory Reserve Volume (ERV), an increase in RV leads to a compensatory increase in FRC. The patient breathes at higher lung volumes to keep the airways open via increased radial traction. **2. Why Other Options are Incorrect:** * **Options A & C:** Residual Volume (RV) is **never reduced** in obstructive diseases like asthma or COPD; it is typically increased. A reduced RV is characteristic of restrictive lung diseases (e.g., pulmonary fibrosis). * **Options C & D:** FRC is **increased** in asthma due to hyperinflation. A reduced FRC occurs in conditions that cause lung collapse or stiffness (e.g., ARDS, obesity, or interstitial lung disease). **High-Yield Clinical Pearls for NEET-PG:** * **PFT Pattern:** Decreased FEV1, decreased FEV1/FVC ratio ( 12% and >200ml improvement in FEV1 after bronchodilator administration. * **Flow-Volume Loop:** Shows a characteristic **"scooped-out"** appearance during the expiratory phase. * **Status Asthmaticus:** A normal or rising PaCO2 in a severe attack is an ominous sign of impending respiratory failure (muscle fatigue).

Q: Which of the following is preferred for the diagnosis of obstructive airway disease?

Timed vital capacity. **Explanation:** The diagnosis of obstructive airway diseases (like Asthma and COPD) relies on assessing the **rate of airflow** rather than just the volume of air. **Why Timed Vital Capacity is correct:** Timed Vital Capacity, specifically **FEV1** (Forced Expiratory Volume in 1 second), measures the volume of air exhaled during the first second of a forced expiration. In obstructive diseases, the airway resistance is increased, leading to a prolonged expiratory phase and a significant reduction in FEV1. While the total Forced Vital Capacity (FVC) may remain normal or slightly decreased, the **FEV1/FVC ratio** (Tiffeneau Index) drops below 70%, making it the gold standard for identifying obstruction. **Why other options are incorrect:** * **Vital Capacity (VC):** This measures the maximum volume of air moved in or out. It is primarily reduced in **restrictive** lung diseases (like Pulmonary Fibrosis). In early obstruction, VC may be normal. * **Tidal Volume (TV):** This is the volume of air inspired or expired during normal quiet breathing (~500ml). It is non-specific and does not provide information about airway resistance or lung capacity. * **Blood Gas Analysis (ABG):** While useful for assessing the severity of an acute exacerbation (hypoxia/hypercapnia), it is not a diagnostic tool for the underlying airway disease itself. **High-Yield Clinical Pearls for NEET-PG:** * **Obstructive Pattern:** ↓FEV1, ↓FEV1/FVC ratio (<0.7), ↑Residual Volume (due to air trapping). * **Restrictive Pattern:** ↓FVC, **Normal or ↑FEV1/FVC ratio**, ↓Total Lung Capacity. * **MVV (Maximum Voluntary Ventilation):** Also significantly reduced in obstructive diseases but is more strenuous for the patient than FEV1.

Question 1

In which of the following conditions would oxygen therapy be most effective in alleviating hypoxia?

Accepted Answer

Emphysema

Answer

Anemia due to blood loss

Answer

Edematous tissues

Answer

Localized circulatory deficiencies

Question 2

Which of the following conditions does not promote the dissociation of O2 from hemoglobin?

Accepted Answer

Increase in the partial pressure of O2

Answer

Decrease in pH

Answer

Increase in 2,3-diphosphoglycerate concentration

Answer

Increase in CO2 concentration

Question 3

Carbon monoxide poisoning is a type of which of the following?

Accepted Answer

Anemic hypoxia

Answer

Histotoxic hypoxia

Answer

Hypoxic hypoxia

Answer

Stagnant hypoxia

Question 4

Which of the following statements about surfactant is false?

Accepted Answer

Consists of 3 types of unique proteins in it.

Answer

Produced by Type II alveolar epithelial cells.

Answer

Contains dipalmitoyl phosphatidylcholine (DPPC) and phosphatidyl glycerol.

Answer

Is a lipid-surface tension lowering agent.

Question 5

What is the normal pulmonary artery pressure?

Accepted Answer

25/8 mm Hg

Answer

120/80 mm Hg

Answer

25/0 mm Hg

Answer

120/0 mm Hg

Question 6

Transport of carbon monoxide (CO) is diffusion limited because?

Accepted Answer

High affinity of CO for hemoglobin

Answer

Alveolar membrane is less permeable to CO

Answer

CO crosses the epithelial barrier slowly

Answer

On exposure to air, there is a sudden increase in partial pressure

Question 7

What is the immediate response of J receptor stimulation?

Accepted Answer

Apnea

Answer

Tachycardia

Answer

Hypertension

Answer

Tachypnea

Question 8

Conducting zone of the respiratory system is defined as:

Accepted Answer

0th generation to 16th generation of airways

Answer

1st generation of airways

Answer

0th generation to 23rd generation of airways

Answer

16th to 23rd generation of airways

Question 9

Which of the following statements is true regarding asthma?

Accepted Answer

Increased FRC and increased residual volume

Answer

Increased FRC and reduced residual volume

Answer

Reduced FRC and reduced residual volume

Answer

Reduced FRC and increased residual volume

Question 10

Which of the following is preferred for the diagnosis of obstructive airway disease?

Accepted Answer

Timed vital capacity

Answer

Vital capacity

Answer

Tidal volume

Answer

Blood gas analysis

Respiratory System — MCQs

Respiratory System — MCQs

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