Respiratory System Practice Questions

Q: A 65-year-old man with COPD undergoes pulmonary function testing. His FEV1 is 65% predicted, and spirometry shows an obstructive pattern. A pressure-volume loop demonstrates reduced elastic recoil with increased total lung capacity. When comparing his lungs to a healthy individual, what physiological change best explains his altered compliance?

Destruction of elastic tissue in alveolar walls. ***Destruction of elastic tissue in alveolar walls*** - In **emphysema**, a component of **COPD**, the destruction of **elastin** by proteases increases lung **compliance**, leading to a floppy, easily distensible lung. - This loss of **elastic recoil** causes the pressure-volume loop to shift upward and to the left, resulting in **increased total lung capacity (TLC)** and air trapping. *Increased alveolar surface tension from surfactant deficiency* - **Surfactant deficiency** increases surface tension, which significantly **decreases lung compliance**, making the lungs difficult to inflate. - This is a hallmark of **Neonatal Respiratory Distress Syndrome**, not the obstructive pattern seen in COPD patients. *Increased collagen deposition in interstitial spaces* - **Collagen deposition** is characteristic of **restrictive lung diseases** like pulmonary fibrosis, which leads to **decreased compliance**. - This would result in a **reduced total lung capacity (TLC)** and a pressure-volume loop shifted downward and to the right. *Pulmonary vascular remodeling* - This refers to thickening of vessel walls and is associated with **pulmonary hypertension**, which primarily affects blood flow and pressures. - While it can occur in late-stage COPD, it does not explain the primary change in **lung compliance** or the increase in TLC. *Bronchial smooth muscle hypertrophy* - This is a feature of **chronic bronchitis** and asthma that contributes to **airway resistance** and the obstructive FEV1/FVC ratio. - While it limits airflow, it does not directly alter the **elasticity** of the lung parenchyma or the lung compliance seen on pressure-volume loops.

Q: Lungs do not collapse during expiration because of the presence of?

Dipalmitoyl phosphatidyl choline. **Explanation:** The correct answer is **Dipalmitoyl phosphatidyl choline (DPPC)**, which is the primary phospholipid component of **Pulmonary Surfactant**. **1. Why DPPC is correct:** According to the **Law of Laplace ($P = 2T/r$)**, smaller alveoli have a higher collapsing pressure ($P$) due to surface tension ($T$). During expiration, as the radius ($r$) of the alveoli decreases, the risk of collapse (atelectasis) increases. Surfactant, secreted by **Type II Pneumocytes**, reduces surface tension. DPPC molecules are amphipathic; they crowd together as the alveolus shrinks, significantly lowering surface tension and preventing the lungs from collapsing at low lung volumes. **2. Why other options are incorrect:** * **Hyaline membrane:** This is a pathological finding (not a physiological one) seen in Neonatal Respiratory Distress Syndrome (NRDS) or ARDS, where protein-rich fluid leaks into alveoli, actually *hindering* gas exchange. * **Macrophages:** Alveolar macrophages (Dust cells) are part of the immune system and are responsible for clearing debris and pathogens; they do not influence surface tension. * **Interstitial fluid:** Excessive fluid in the interstitium leads to pulmonary edema, which decreases lung compliance and impairs respiration. **Clinical Pearls for NEET-PG:** * **L/S Ratio:** A Lecithin (DPPC) to Sphingomyelin ratio of **>2:1** in amniotic fluid indicates fetal lung maturity. * **Glucocorticoids:** These are administered to mothers in preterm labor to accelerate surfactant production by stimulating Type II pneumocytes. * **Surfactant Proteins:** SP-A and SP-D are involved in innate immunity, while SP-B and SP-C are essential for the film-forming properties of surfactant.

Q: What is the partial pressure of O2, which constitutes approximately 21% of inspired air?

160 mmHg. **Explanation:** The partial pressure of a gas in a mixture is determined by **Dalton’s Law**, which states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases. To calculate the partial pressure of Oxygen ($PO_2$) in dry inspired air at sea level: 1. **Total Atmospheric Pressure ($P_{atm}$):** 760 mmHg. 2. **Fraction of Oxygen ($FiO_2$):** 21% or 0.21. 3. **Calculation:** $PO_2 = P_{atm} \times FiO_2 = 760 \times 0.21 \approx \mathbf{159.6 \text{ mmHg}}$ (rounded to **160 mmHg**). **Analysis of Incorrect Options:** * **B (240 mmHg):** This value does not correspond to any physiological gas pressure at sea level under normal atmospheric conditions. * **C (580 mmHg):** This is the approximate partial pressure of **Nitrogen** ($PN_2$) in the atmosphere ($760 \times 0.79$). * **D (760 mmHg):** This represents the **total atmospheric pressure** at sea level, not the pressure of an individual gas component. **NEET-PG High-Yield Pearls:** * **Humidification Effect:** As air enters the upper airways, it is saturated with water vapor ($PH_2O = 47 \text{ mmHg}$). The $PO_2$ in **humidified tracheal air** drops to $\approx 149 \text{ mmHg}$ $[(760 - 47) \times 0.21]$. * **Alveolar Air:** In the alveoli, $PAO_2$ is further reduced to $\approx \mathbf{100 \text{ mmHg}}$ due to the continuous diffusion of $O_2$ into the blood and the addition of $CO_2$. * **Fractional Concentration:** Note that while partial pressure changes with altitude, the *percentage* of $O_2$ (21%) remains constant.

Q: What is the most important form of carbon dioxide transport in the blood?

Bicarbonates. **Explanation:** Carbon dioxide (CO₂) is transported from the tissues to the lungs in three primary forms. Understanding the distribution of these forms is a high-yield concept for NEET-PG: 1. **Bicarbonate Ions (70%):** This is the **most important and predominant form**. CO₂ enters RBCs and 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 diffuses into the plasma in exchange for chloride ions (the **Chloride Shift** or Hamburger phenomenon). 2. **Carbamino Compounds (23%):** CO₂ binds directly to the amino groups of hemoglobin (forming **carbaminohemoglobin**) and plasma proteins. 3. **Dissolved Form (7%):** A small fraction is carried physically dissolved in the plasma. **Analysis of Incorrect Options:** * **A. Carboxyhemoglobin:** This is a trap. Carboxyhemoglobin refers to **Carbon Monoxide (CO)** bound to hemoglobin, which is a toxic state, not a physiological CO₂ transport mechanism. * **B. Dissolved CO₂:** While CO₂ is 20 times more soluble than oxygen, this form only accounts for ~7% of total transport. * **D. CO₂ molecules attached to hemoglobin:** This refers to carbaminohemoglobin. While significant (23%), it is not the "most important" or majority form. **High-Yield Clinical Pearls:** * **Haldane Effect:** Deoxygenation of blood increases its ability to carry CO₂. In the lungs, when $O_2$ binds to Hb, it promotes the release of CO₂. * **Carbonic Anhydrase:** It is one of the fastest enzymes in the body; its absence would make CO₂ transport insufficient to sustain life. * **Chloride Shift:** Remember that $Cl^-$ moves **into** the RBC in systemic tissues and **out** of the RBC in pulmonary capillaries.

Q: Type 1 glomus cells secrete neurotransmitters in response to oxygen levels due to the function of which channel?

K+ channel. **Explanation:** The **Type 1 Glomus cells** (chief cells) of the carotid and aortic bodies act as peripheral chemosensors. The primary mechanism of oxygen sensing involves **Oxygen-sensitive Potassium (K+) channels**. **Mechanism of Action:** 1. **Hypoxia:** When arterial $PO_2$ falls, these oxygen-sensitive K+ channels **close**. 2. **Depolarization:** The reduction in K+ efflux leads to the accumulation of positive charge inside the cell, causing membrane depolarization. 3. **Neurotransmitter Release:** Depolarization opens voltage-gated **Calcium (Ca²⁺) channels**, leading to an influx of Calcium and subsequent exocytosis of neurotransmitters (primarily **Dopamine**, but also ACh and ATP). 4. **Afferent Signaling:** These transmitters stimulate the glossopharyngeal (CN IX) and vagus (CN X) nerves to increase the respiratory rate. **Analysis of Options:** * **D (Correct):** K+ channels are the "sensors" that initiate the electrical response to hypoxia. * **A (Incorrect):** While Na+ channels are involved in action potential propagation, they are not the primary oxygen-sensing mechanism. * **B (Incorrect):** Cl- channels do not play a significant role in the initial depolarization phase of glomus cells. * **C (Incorrect):** Ca²⁺ channels are the *effectors* that lead to neurotransmitter release, but they open only *after* the K+ channels have closed and the cell has depolarized. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Carotid bodies (bifurcation of common carotid) and Aortic bodies (arch of aorta). * **Stimuli:** Peripheral chemoreceptors respond to **decreased $PO_2$** (<60 mmHg), **increased $PCO_2$**, and **decreased pH**. * **Nerve Supply:** Carotid body via **Hering’s nerve** (branch of CN IX); Aortic body via CN X. * **Key Difference:** Central chemoreceptors (medulla) do **not** respond to hypoxia; they respond primarily to changes in $H^+$ concentration in the CSF derived from arterial $CO_2$.

Q: All of the following are risks seen in the administration of pure oxygen to hypoxic patients, except?

2,3-DPG toxicity. **Explanation:** The correct answer is **C. 2,3-DPG toxicity**. This is because 2,3-DPG (2,3-bisphosphoglycerate) is a metabolic byproduct of glycolysis in red blood cells that helps regulate hemoglobin's affinity for oxygen. It is not a substance that causes "toxicity" during oxygen therapy. In fact, chronic hypoxia typically *increases* 2,3-DPG levels to facilitate oxygen unloading to tissues. **Analysis of Options:** * **A. Apnea (Hypoxic Drive):** In patients with chronic hypercapnia (e.g., COPD), the central chemoreceptors become desensitized. Their primary stimulus for breathing becomes "hypoxic drive" via peripheral chemoreceptors. Administering pure oxygen removes this stimulus, potentially leading to respiratory depression or apnea. * **B. Pulmonary Edema:** High concentrations of oxygen (hyperoxia) lead to the formation of Reactive Oxygen Species (ROS) like superoxide radicals. These damage the alveolar-capillary membrane, leading to "Oxygen Toxicity" (Lorrain Smith effect), which manifests as pulmonary congestion and edema. * **D. Convulsions:** Exposure to high partial pressures of oxygen (hyperbaric oxygen) can affect the Central Nervous System (Paul Bert effect), leading to symptoms such as dizziness, muscle twitching, and generalized seizures (convulsions). **High-Yield Clinical Pearls for NEET-PG:** 1. **Absorption Atelectasis:** Pure oxygen can wash out nitrogen (which normally keeps alveoli splinted open), leading to alveolar collapse. 2. **Retinopathy of Prematurity (ROP):** In neonates, excessive oxygen therapy causes retinal vasoconstriction followed by abnormal vascular proliferation. 3. **Haldane Effect:** High $O_2$ promotes the displacement of $CO_2$ from hemoglobin, which can acutely worsen hypercapnia in certain patients.

Q: What is the major role of 2,3-DPG in red blood cells?

Release of O2. **Explanation:** The correct answer is **B. Release of O2**. **Underlying Concept:** 2,3-Diphosphoglycerate (2,3-DPG) is a byproduct of the Rapoport-Luebering shunt in glycolysis. Its primary function is to act as an allosteric effector that binds to the beta chains of **deoxyhemoglobin**. By binding to the central cavity of the hemoglobin tetramer, it stabilizes the **"T" (Tense) state**, which has a low affinity for oxygen. This stabilization shifts the Oxygen-Hemoglobin Dissociation Curve to the **right**, facilitating the unloading (release) of oxygen to the peripheral tissues. **Analysis of Incorrect Options:** * **A. Binding of O2:** 2,3-DPG actually *decreases* the affinity of hemoglobin for oxygen. Increased levels of 2,3-DPG make it harder for oxygen to bind, not easier. * **C. Acid-base balance:** While hemoglobin acts as a buffer (Bohr effect), 2,3-DPG itself is not a primary regulator of systemic acid-base balance. * **D. Reversal of glycolysis:** 2,3-DPG is an intermediate/byproduct of glycolysis; it does not reverse the pathway. **High-Yield Clinical Pearls for NEET-PG:** * **Right Shift Factors (CADET, face Right!):** **C**O2 increase, **A**cidosis (H+), **D**PG increase, **E**xercise, and **T**emperature increase. * **Fetal Hemoglobin (HbF):** HbF has a **lower affinity** for 2,3-DPG because its gamma chains lack the specific binding site found in adult beta chains. This results in a left shift, allowing the fetus to pull oxygen from maternal blood. * **Stored Blood:** Levels of 2,3-DPG **decrease** in stored blood. Transfusing large amounts of "old" blood can lead to poor tissue oxygenation because the hemoglobin holds onto oxygen too tightly (Left shift).

Question 1

A 65-year-old man with COPD undergoes pulmonary function testing. His FEV1 is 65% predicted, and spirometry shows an obstructive pattern. A pressure-volume loop demonstrates reduced elastic recoil with increased total lung capacity. When comparing his lungs to a healthy individual, what physiological change best explains his altered compliance?

Accepted Answer

Destruction of elastic tissue in alveolar walls

Answer

Increased alveolar surface tension from surfactant deficiency

Answer

Increased collagen deposition in interstitial spaces

Answer

Pulmonary vascular remodeling

Answer

Bronchial smooth muscle hypertrophy

Question 2

Lungs do not collapse during expiration because of the presence of?

Accepted Answer

Dipalmitoyl phosphatidyl choline

Answer

Hyaline membrane

Answer

Macrophages

Answer

Interstitial fluid

Question 3

Given an arterial blood oxygen content of 20 mL per 100 mL of blood and a venous blood oxygen content of 15 mL per 100 mL of blood, calculate the amount of oxygen transferred from the blood to the tissues if the blood flow is 200 mL/min?

Accepted Answer

10 mL/min

Answer

5 mL/min

Answer

15 mL/min

Answer

20 mL/min

Question 4

What is the partial pressure of O2, which constitutes approximately 21% of inspired air?

Accepted Answer

160 mmHg

Answer

240 mmHg

Answer

580 mmHg

Answer

760 mmHg

Question 5

What is the most important form of carbon dioxide transport in the blood?

Accepted Answer

Bicarbonates

Answer

Carboxyhemoglobin

Answer

Dissolved CO2

Answer

CO2 molecules attached to hemoglobin

Question 6

100% oxygen is not effective in which of the following conditions?

Accepted Answer

Tetralogy of Fallot

Answer

Pulmonary edema

Answer

Myocardial infarction

Answer

COPD

Question 7

Which of the following statements is true concerning normal expiration during resting conditions?

Accepted Answer

The flow velocity of gas in the large airways exceeds that in the terminal bronchioles.

Answer

Expiration is generated by the contraction of expiratory muscles.

Answer

Alveolar pressure is less than atmospheric pressure.

Answer

Intrapleural pressure gradually falls (becomes more negative) during expiration.

Question 8

Type 1 glomus cells secrete neurotransmitters in response to oxygen levels due to the function of which channel?

Accepted Answer

K+ channel

Answer

Na+ channel

Answer

Cl- channel

Answer

Ca+2 channel

Question 9

All of the following are risks seen in the administration of pure oxygen to hypoxic patients, except?

Accepted Answer

2,3-DPG toxicity

Answer

Apnea occurs due to hypostimulation of peripheral receptors

Answer

Pulmonary edema

Answer

Convulsions

Question 10

What is the major role of 2,3-DPG in red blood cells?

Accepted Answer

Release of O2

Answer

Binding of O2

Answer

Acid-base balance

Answer

Reversal of glycolysis

Respiratory System — MCQs

Respiratory System — MCQs

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