Respiratory System Practice Questions

Q: Surfactant acts on which part of the respiratory system?

Alveoli. **Explanation:** **1. Why Alveoli is Correct:** Pulmonary surfactant is a surface-active lipoprotein complex (primarily Dipalmitoylphosphatidylcholine - DPPC) secreted by **Type II Pneumocytes** in the alveolar epithelium. Its primary function is to **reduce surface tension** at the air-liquid interface within the **alveoli**. According to the **Law of Laplace ($P = 2T/r$)**, smaller spheres have a higher collapsing pressure. By reducing surface tension ($T$), surfactant prevents the collapse of smaller alveoli during expiration (atelectasis), increases lung compliance, and reduces the work of breathing. **2. Why Other Options are Incorrect:** * **Bronchi and Trachea (Options A & D):** These are part of the conducting zone and are structurally supported by **cartilage**. They do not rely on surface tension management to remain patent; their rigid walls prevent collapse. * **Bronchioles (Option C):** While bronchioles lack cartilage, they are kept open by smooth muscle tone and the radial traction of surrounding lung parenchyma. Surfactant is specifically functional at the terminal gas-exchange units (alveoli) where the air-fluid interface is most critical. **3. High-Yield Clinical Pearls for NEET-PG:** * **Composition:** 90% lipids (mainly **DPPC/Lecithin**) and 10% proteins (SP-A, B, C, D). * **Synthesis:** Starts around 24–28 weeks of gestation; reaches maturity by **35 weeks**. * **L/S Ratio:** A Lecithin/Sphingomyelin ratio **> 2** in amniotic fluid indicates fetal lung maturity. * **Clinical Correlation:** Deficiency of surfactant leads to **Infant Respiratory Distress Syndrome (IRDS)** or Hyaline Membrane Disease, characterized by widespread alveolar collapse. * **Glucocorticoids:** These are administered to mothers in preterm labor to accelerate surfactant production by stimulating Type II pneumocytes.

Q: What are the non-respiratory functions of the lungs?

All of the above.. The lungs are not merely organs for gas exchange; they serve as a vital metabolic and filtration hub. The correct answer is **D (All of the above)** because the pulmonary circulation is involved in several homeostatic processes: 1. **Sodium Balance:** The lungs are the primary site for the conversion of Angiotensin I to Angiotensin II via the **Angiotensin-Converting Enzyme (ACE)** located on the luminal surface of pulmonary capillary endothelial cells. Angiotensin II stimulates aldosterone secretion, which regulates sodium reabsorption in the kidneys. 2. **Fibrinolytic Function:** The pulmonary endothelium produces substances like **plasminogen activator**, which helps dissolve small clots (thrombi) before they can enter the systemic circulation and cause arterial emboli. 3. **Secretion of Heparin:** The lungs contain a high concentration of **mast cells** in the connective tissue. these cells secrete heparin, a potent anticoagulant that helps maintain blood fluidity and prevents micro-clot formation within the pulmonary vasculature. **Why other options are not "wrong":** In this "All of the above" format, each individual option represents a documented non-respiratory function. Therefore, selecting only one would be incomplete. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir Function:** The lungs act as a blood reservoir, holding ~500ml of blood (9% of total volume). * **Inactivation Site:** The lungs inactivate **Bradykinin, Serotonin, and Prostaglandins (E & F)**, but they do **not** inactivate Epinephrine or Angiotensin II. * **Filtration:** They act as a "sieve" for air bubbles, fat globules, and small emboli.

Q: The Bohr effect is associated with the effect of which of the following on oxygen affinity?

pH. **Explanation:** The **Bohr effect** describes the physiological phenomenon where an increase in blood CO₂ concentration or a decrease in **pH** (increased acidity) leads to a decrease in hemoglobin’s affinity for oxygen. This causes the oxygen-hemoglobin dissociation curve to shift to the **right**, facilitating the unloading of oxygen to metabolically active tissues. **Why pH is the correct answer:** In tissues with high metabolic activity, CO₂ is produced, which reacts with water to form carbonic acid, subsequently dissociating into H⁺ ions and bicarbonate. These H⁺ ions bind to specific amino acid residues on the hemoglobin molecule (primarily histidine), stabilizing the **T-state (Tense state)** or deoxygenated form. This reduces its affinity for O₂, allowing oxygen to be released where it is needed most. **Analysis of Incorrect Options:** * **A. Temperature:** While an increase in temperature does shift the curve to the right (decreasing affinity), this is a direct kinetic effect on the bond between hemoglobin and oxygen, not the Bohr effect. * **C. 2,3 BPG:** 2,3-Bisphosphoglycerate is a byproduct of glycolysis that stabilizes the T-state. While it decreases O₂ affinity, this is a distinct regulatory mechanism separate from the pH-driven Bohr effect. **High-Yield Clinical Pearls for NEET-PG:** 1. **Bohr vs. Haldane Effect:** Remember, **B**ohr = **B**lood/Tissues (CO₂/H⁺ affecting O₂ affinity). **H**aldane = **H**ematosis/Lungs (O₂ affecting CO₂ affinity). 2. **Right Shift Factors:** "CADET, face Right!" (**C**O₂, **A**cid/H⁺, **D**PG/2,3-BPG, **E**xercise, **T**emperature). 3. **P50:** The Bohr effect increases the P50 value (the partial pressure of O₂ at which hemoglobin is 50% saturated).

Q: CO2 is mainly transported in the blood in which form?

Bicarbonate (HCO3-). **Explanation:** Carbon dioxide ($CO_2$) is a metabolic waste product transported from the tissues to the lungs via three primary mechanisms. Understanding the distribution of these forms is a high-yield topic for NEET-PG. **1. Why Bicarbonate ($HCO_3^-$) is Correct:** The majority of $CO_2$ (**approximately 70%**) is transported as bicarbonate ions. When $CO_2$ enters red blood cells (RBCs), it reacts with water to form carbonic acid ($H_2CO_3$), a reaction catalyzed by the enzyme **Carbonic Anhydrase**. This acid then dissociates into $H^+$ and $HCO_3^-$. The bicarbonate then exits the RBC into the plasma in exchange for Chloride ions (known as the **Chloride Shift or Hamburger Phenomenon**). **2. Analysis of Incorrect Options:** * **A. Dissolved form:** Only about **7%** of $CO_2$ is transported dissolved in physical solution in the plasma. While $CO_2$ is 20 times more soluble than Oxygen, this remains a minor transport pathway. * **C. Carbamino compound:** About **23%** of $CO_2$ binds directly to the amino groups of hemoglobin to form **carbaminohemoglobin**. Note: $CO_2$ does *not* bind to the iron (heme) site, unlike Oxygen or Carbon Monoxide. * **D. Gas form:** $CO_2$ does not travel through the blood as free gas bubbles; it must be dissolved or chemically modified to maintain blood stability. **High-Yield Clinical Pearls for NEET-PG:** * **Haldane Effect:** Deoxygenation of blood increases its ability to carry $CO_2$. This occurs in the tissues. * **Chloride Shift:** To maintain electrical neutrality, as $HCO_3^-$ leaves the RBC, $Cl^-$ enters. This causes RBCs to swell slightly in venous blood. * **Enzyme:** Carbonic Anhydrase is one of the fastest enzymes in the body and is absent in plasma (it is localized within RBCs).

Q: What is the TRUE statement regarding the measurement of anatomical dead space?

1 mL of dead space per pound of ideal body weight. ### Explanation **Conceptual Basis** Anatomical dead space refers to the volume of the conducting airways (from the nose/mouth down to the terminal bronchioles) where no gas exchange occurs because there are no alveoli. In a healthy adult, this volume is remarkably consistent relative to body size. The standard physiological rule of thumb is that anatomical dead space is approximately **1 mL per pound (lb)** of ideal body weight (or roughly 2.2 mL/kg). For a typical 150 lb (70 kg) adult, the anatomical dead space is approximately 150 mL. **Analysis of Options** * **Option A (Correct):** This aligns with the established physiological constant. It is the most accurate estimation used in clinical practice and respiratory physiology equations (e.g., calculating alveolar ventilation: $\dot{V}_A = (V_T - V_D) \times f$). * **Options B, C, and D (Incorrect):** These values (5, 10, and 15 mL/lb) significantly overestimate the dead space. If dead space were this high, a person would need an impossibly large tidal volume just to ensure any fresh air reached the alveoli. **High-Yield NEET-PG Pearls** * **Fowler’s Method:** Anatomical dead space is measured using the **Single Breath Nitrogen Washout** technique. * **Bohr’s Equation:** This is used to measure **Physiological Dead Space** (which includes anatomical dead space plus alveolar dead space). It uses arterial $CO_2$ ($PaCO_2$) and expired $CO_2$ ($PeCO_2$). * **Anatomical vs. Physiological:** In healthy individuals, anatomical and physiological dead space are nearly equal. However, in diseases like COPD or Pulmonary Embolism, physiological dead space increases significantly due to ventilation-perfusion (V/Q) mismatch. * **Positioning:** Anatomical dead space increases in the upright position and during deep inspiration.

Q: Oxygen carrying capacity of blood is largely determined by what?

Hemoglobin level. **Explanation:** The oxygen-carrying capacity of blood refers to the maximum amount of oxygen that can be transported by a specific volume of blood. In the human body, oxygen is transported in two forms: dissolved in plasma (approx. 1.5%) and bound to hemoglobin (approx. 98.5%). **Why Hemoglobin level is correct:** Each gram of pure hemoglobin (Hb) can bind approximately **1.34 mL of oxygen** (Hüfner's constant). The formula for oxygen content is: *Oxygen Content = (1.34 × [Hb] × SaO₂) + (0.003 × PaO₂)* Since the vast majority of oxygen is chemically bound to hemoglobin, the total concentration of hemoglobin is the primary limiting factor and determinant of the blood's capacity to carry oxygen. **Why other options are incorrect:** * **Amount of CO2 (B) and Acidosis (C):** These factors influence the **Oxygen-Hemoglobin Dissociation Curve** (Bohr Effect). They affect the *affinity* of hemoglobin for oxygen (how easily it is released), but they do not change the total *capacity* of the blood to carry oxygen. * **Plasma concentration (D):** Oxygen is poorly soluble in plasma. At normal physiological pressure, only 0.003 mL of O₂ dissolves in 100 mL of plasma per mmHg of PO₂. This contribution is negligible compared to the role of hemoglobin. **High-Yield NEET-PG Pearls:** * **Normal Oxygen Capacity:** In a healthy adult with 15g/dL of Hb, the capacity is approximately **20.1 mL O₂/100 mL blood**. * **Anemia vs. CO Poisoning:** In anemia, the O₂ capacity is decreased because Hb levels are low. In Carbon Monoxide (CO) poisoning, the O₂ capacity is decreased because CO occupies the binding sites, even if the Hb level is numerically normal. * **P50 Value:** The partial pressure of oxygen at which hemoglobin is 50% saturated (normally 26.7 mmHg). A "Right Shift" (caused by ↑CO₂, ↑H+, ↑Temp, ↑2,3-BPG) decreases affinity but does not change total capacity.

Q: Oxygen therapy is most useful in which of the following types of hypoxia?

Hypoxic hypoxia. **Explanation:** The primary goal of oxygen therapy is to increase the partial pressure of oxygen in the alveoli ($PAO_2$), which in turn increases the arterial partial pressure of oxygen ($PaO_2$). **Why Hypoxic Hypoxia is the correct answer:** Hypoxic hypoxia is characterized by a low $PaO_2$ due to factors like high altitude, hypoventilation, or V/Q mismatch. Since the underlying problem is a lack of oxygen tension in the arterial blood, increasing the inspired oxygen concentration ($FiO_2$) directly corrects the gradient, significantly improving oxygen saturation. It is the only type of hypoxia where oxygen therapy is highly effective. **Analysis of Incorrect Options:** * **Anemic Hypoxia:** The $PaO_2$ is normal, but the oxygen-carrying capacity is reduced due to low hemoglobin or CO poisoning. Oxygen therapy adds only a negligible amount of dissolved oxygen in the plasma; it does not fix the hemoglobin deficit. * **Stagnant (Ischemic) Hypoxia:** The $PaO_2$ and content are normal, but blood flow to tissues is inadequate (e.g., heart failure, shock). The solution is improving cardiac output or local perfusion, not increasing inspired oxygen. * **Histotoxic Hypoxia:** Oxygen delivery is normal, but tissues (e.g., in cyanide poisoning) cannot utilize it because the cytochrome oxidase system is inhibited. Oxygen therapy is generally ineffective as the "machinery" is broken. **High-Yield Clinical Pearls for NEET-PG:** * **Cyanosis** is most marked in stagnant hypoxia and absent in anemic hypoxia (as 5g% of reduced Hb is required to see cyanosis). * **$PaO_2$** is normal in all types of hypoxia except **Hypoxic Hypoxia**. * In **CO poisoning** (a form of anemic hypoxia), 100% hyperbaric oxygen is used not just to increase dissolved $O_2$, but to displace CO from hemoglobin.

Q: During inspiration, the diaphragm:

Contracts. **Explanation:** **1. Why Option A is Correct:** Inspiration is an **active process** primarily driven by the contraction of the diaphragm (the chief muscle of respiration). When the diaphragm **contracts**, its dome flattens and moves inferiorly (downward). This action increases the **vertical diameter** of the thoracic cavity. According to **Boyle’s Law** (Pressure ∝ 1/Volume), the increase in thoracic volume leads to a decrease in intra-alveolar pressure (becoming sub-atmospheric). This pressure gradient causes air to flow from the atmosphere into the lungs. **2. Why Other Options are Incorrect:** * **Option B (Relaxes):** Diaphragmatic relaxation occurs during **expiration**. As the muscle relaxes, it resumes its dome shape, decreasing thoracic volume and pushing air out of the lungs (a passive process during quiet breathing). * **Option C (Does nothing):** The diaphragm is the most essential muscle for ventilation; it is never static during the respiratory cycle. * **Option D (Expands):** In physiological terms, muscles either contract or relax. While the thoracic cavity "expands," the muscle itself "contracts" to facilitate that expansion. **3. NEET-PG High-Yield Clinical Pearls:** * **Innervation:** The diaphragm is supplied by the **Phrenic Nerve (C3, C4, C5)**. Remember: *"C3, 4, 5 keep the diaphragm alive."* * **Movement:** During quiet inspiration, the diaphragm moves down by ~1 cm; during deep inspiration, it can move up to 10 cm. * **Anatomical Openings:** Remember the levels of major structures passing through the diaphragm: **I8** (IVC at T8), **10E** (Esophagus at T10), and **A12** (Aorta at T12). * **Paradoxical Respiration:** If the phrenic nerve is paralyzed, the diaphragm moves *upward* during inspiration (sucked up by negative pressure), known as paradoxical movement.

Question 1

Which of the following statements are true about interstitial fibrosis?

Accepted Answer

FEV1/FVC ratio is decreased

Answer

FVC decreased

Answer

FEV1/FVC ratio is normal or increased

Answer

FRC is normal

Question 2

Surfactant acts on which part of the respiratory system?

Accepted Answer

Alveoli

Answer

Bronchi

Answer

Bronchioles

Answer

Trachea

Question 3

What are the non-respiratory functions of the lungs?

Accepted Answer

All of the above.

Answer

Sodium balance.

Answer

Fibrinolytic function.

Answer

Secretion of heparin.

Question 4

The Bohr effect is associated with the effect of which of the following on oxygen affinity?

Accepted Answer

pH

Answer

Temperature

Answer

2,3 BPG

Answer

None of the above

Question 5

CO2 is mainly transported in the blood in which form?

Accepted Answer

Bicarbonate (HCO3-)

Answer

Dissolved form

Answer

Carbamino compound

Answer

Gas form

Question 6

What is the TRUE statement regarding the measurement of anatomical dead space?

Accepted Answer

1 mL of dead space per pound of ideal body weight

Answer

5 mL of dead space per pound of ideal body weight

Answer

10 mL of dead space per pound of ideal body weight

Answer

15 mL of dead space per pound of ideal body weight

Question 7

Oxygen carrying capacity of blood is largely determined by what?

Accepted Answer

Hemoglobin level

Answer

Amount of CO2 in blood

Answer

Acidosis

Answer

Plasma concentration

Question 8

Oxygen therapy is most useful in which of the following types of hypoxia?

Accepted Answer

Hypoxic hypoxia

Answer

Anemic hypoxia

Answer

Stagnant hypoxia

Answer

Histotoxic hypoxia

Question 9

During inspiration, the diaphragm:

Accepted Answer

Contracts

Answer

Relaxes

Answer

Does nothing

Answer

Expands

Question 10

Peripheral chemoreceptors are maximally stimulated by which type of hypoxia?

Accepted Answer

Histotoxic hypoxia

Answer

Hypoxic hypoxia

Answer

Stagnant hypoxia

Answer

Anemic hypoxia

Respiratory System — MCQs

Respiratory System — MCQs

On this page

Practice by Chapter

Want unlimited practice?