Respiratory System Practice Questions

Q: In the presence of vasopressin, what is the greatest fraction of filtered water absorbed?

Proximal tubule. **Explanation:** The correct answer is **Proximal Tubule (A)**. This question tests the understanding of obligatory versus facultative water reabsorption in the nephron. 1. **Why Proximal Tubule is Correct:** Regardless of the presence or absence of Vasopressin (ADH), the **Proximal Convoluted Tubule (PCT)** is the site of the greatest water reabsorption. Approximately **65-70%** of the filtered water is reabsorbed here via osmosis, following the active transport of sodium (iso-osmotic reabsorption). This is known as **obligatory water reabsorption** and occurs independently of ADH levels. 2. **Why Incorrect Options are Wrong:** * **Loop of Henle (B):** About 15% of filtered water is reabsorbed in the descending limb. The ascending limb is impermeable to water. * **Distal Tubule (C):** Only a small fraction (approx. 5%) of water is reabsorbed here. * **Collecting Duct (D):** This is the site of **facultative water reabsorption** mediated by Vasopressin (via V2 receptors and Aquaporin-2 channels). While Vasopressin significantly increases the permeability of this segment, the total volume reabsorbed here is only about **10-15%** of the filtered load. Even under maximal ADH stimulation, it never exceeds the volume reabsorbed by the PCT. **High-Yield Clinical Pearls for NEET-PG:** * **Iso-osmotic Reabsorption:** The fluid leaving the PCT is always iso-osmotic to plasma (290-300 mOsm/L). * **V2 Receptors:** Vasopressin acts on V2 receptors in the late distal tubule and collecting ducts to insert **Aquaporin-2** channels. * **Free Water Clearance:** In the absence of ADH (e.g., Diabetes Insipidus), the collecting duct remains impermeable to water, leading to the excretion of large volumes of dilute urine.

Q: What change occurs in blood as it passes through systemic capillaries, EXCEPT for one of the following?

Shift of oxygen dissociation curve to the left. ### Explanation In systemic capillaries, blood undergoes specific physiological changes as it exchanges gases and solutes with tissues. **Why Option C is the Correct Answer (The Exception):** As blood passes through systemic capillaries, it picks up **CO₂** and **H⁺ ions** (metabolic byproducts). This increase in $PCO_2$ and decrease in pH causes a **Rightward Shift** of the Oxygen Dissociation Curve (ODC), known as the **Bohr Effect**. A right shift decreases hemoglobin's affinity for oxygen, facilitating oxygen unloading to the tissues. Therefore, a "shift to the left" is incorrect in this context. **Analysis of Incorrect Options:** * **A. Increase in hematocrit:** As $CO_2$ enters RBCs, it is converted to $HCO_3^-$ and $H^+$. The $HCO_3^-$ exits the cell in exchange for $Cl^-$ (**Chloride Shift/Hamburger Phenomenon**). This increase in intracellular osmotically active particles causes water to enter the RBCs, making them swell and slightly increasing the hematocrit in venous blood. * **B. pH decreases:** Tissues produce $CO_2$, which reacts with water to form carbonic acid ($H_2CO_3$), which dissociates into $H^+$ and $HCO_3^-$. This increase in $H^+$ concentration lowers the blood pH. * **D. Increase in protein content:** Due to hydrostatic pressure in the capillaries, some fluid (plasma) filters into the interstitial space, while large proteins remain in the vessel. This slight loss of fluid leads to a relative increase in the concentration of plasma proteins in the venous end. **High-Yield NEET-PG Pearls:** * **Right Shift (CADET, face Right!):** **C**O₂, **A**cidosis, **D**PG (2,3-BPG), **E**xercise, and **T**emperature all increase in systemic capillaries and shift the ODC to the right. * **Chloride Shift:** Occurs in systemic capillaries ($Cl^-$ moves into RBCs). * **Reverse Chloride Shift:** Occurs in pulmonary capillaries ($Cl^-$ moves out of RBCs).

Q: If pulmonary arterial pressure > alveolar pressure > venous pressure (Pa > Palv > Pv), under normal circumstances, which zone of the lung is being described?

Zone II. **Explanation:** The distribution of pulmonary blood flow is determined by the relationship between three pressures: **Pulmonary Arterial Pressure (Pa)**, **Alveolar Pressure (Palv)**, and **Pulmonary Venous Pressure (Pv)**. This concept is known as West’s Zones of the lung. **Why Zone II is correct:** In **Zone II (the middle zone)**, the relationship is **Pa > Palv > Pv**. Here, arterial pressure is high enough to overcome alveolar pressure, but alveolar pressure is higher than venous pressure. This creates a "Starling Resistor" or "Waterfall effect," where blood flow is determined by the difference between arterial and alveolar pressure, rather than the usual arterial-venous gradient. Flow occurs intermittently, primarily during systole. **Analysis of Incorrect Options:** * **Zone I (Palv > Pa > Pv):** Alveolar pressure exceeds arterial pressure, compressing the capillaries and resulting in no blood flow (Physiological Dead Space). This is not found under normal conditions but occurs in hemorrhage or positive pressure ventilation. * **Zone III (Pa > Pv > Palv):** Both arterial and venous pressures exceed alveolar pressure. The capillaries remain permanently open, and blood flow is continuous and highest here due to gravity. * **Zone IV:** This is a pathological zone (often seen in pulmonary edema) where interstitial pressure exceeds other pressures, reducing flow at the extreme lung bases. **High-Yield Pearls for NEET-PG:** * **Gravity Effect:** Blood flow and ventilation both increase as you move from the apex to the base, but blood flow increases more steeply. * **V/Q Ratio:** Highest at the **Apex** (~3.3) and lowest at the **Base** (~0.6). * **Postural Change:** In a supine position, the lung behaves entirely as Zone III. Zone I is typically only seen in upright individuals with low pulmonary pressures.

Q: What is true for restrictive lung disease?

FEV1/FVC increased, compliance decreased. **Explanation** In **Restrictive Lung Disease (RLD)**, such as interstitial lung disease or pulmonary fibrosis, the primary pathology is a reduction in lung expansion. 1. **Compliance:** The lungs become "stiff" due to fibrosis or chest wall restrictions. This leads to a **decrease in lung compliance** (the ability of the lungs to stretch), making it harder to inhale and reducing the Total Lung Capacity (TLC). 2. **FEV1/FVC Ratio:** While both the Forced Expiratory Volume in 1 second (FEV1) and the Forced Vital Capacity (FVC) decrease, the **FVC decreases more significantly** than the FEV1. Additionally, increased radial traction from fibrotic tissue keeps the airways open during expiration. Consequently, the **FEV1/FVC ratio is either normal or increased** (typically >0.7 or 70%). **Analysis of Incorrect Options:** * **Option A & C:** A **decreased FEV1/FVC ratio** is the hallmark of **Obstructive Lung Diseases** (e.g., Asthma, COPD), where airway resistance is increased. * **Option B & C:** **Increased compliance** is characteristic of **Emphysema**, where the destruction of alveolar elastic fibers makes the lungs overly distensible but prone to collapse during expiration. **High-Yield Clinical Pearls for NEET-PG:** * **Flow-Volume Loop:** In RLD, the loop shifts to the **right** and appears "tall and narrow" (Witch’s Hat appearance). * **Total Lung Capacity (TLC):** A reduction in TLC is the gold standard for diagnosing restriction. * **Radial Traction:** In fibrosis, increased elastic recoil (radial traction) increases expiratory flow rates relative to lung volume, explaining the supranormal FEV1/FVC ratio.

Q: Which nucleus is primarily responsible for the generation of the respiratory rhythm?

Pre-Botzinger Complex. **Explanation:** The generation of the respiratory rhythm is a complex process controlled by the medullary respiratory centers. **1. Why Pre-Bötzinger Complex is correct:** The **Pre-Bötzinger Complex (pre-BötC)**, located in the upper part of the Ventral Respiratory Group (VRG) in the medulla, is considered the **pacemaker of respiration**. It contains a cluster of interneurons that display spontaneous, rhythmic discharges. These neurons initiate the basic respiratory rhythm, which is then transmitted to the motor neurons controlling the diaphragm and other inspiratory muscles. **2. Why other options are incorrect:** * **Pneumotaxic Centre:** Located in the upper pons (Nucleus Parabrachialis), its primary role is to act as an "off-switch" for inspiration. It limits the duration of inspiration, thereby increasing the respiratory rate. * **Dorsal Respiratory Group (DRG):** Located in the Nucleus Tractus Solitarius (NTS), the DRG is primarily responsible for **inspiration**. While it sends the basic motor drive to the diaphragm, it does not generate the rhythm itself; it receives input from the pre-BötC. * **Apneustic Centre:** Located in the lower pons, it promotes long, deep inspirations (apneustic breathing) by delaying the "off-switch" signal. It is normally inhibited by the pneumotaxic center. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Pre-BötC is situated between the nucleus ambiguus and the lateral reticular nucleus. * **Opioid Sensitivity:** This complex is highly sensitive to **opioids and barbiturates**, which is why respiratory depression is a hallmark of overdose. * **Hering-Breuer Reflex:** This is a protective reflex that prevents over-inflation of the lungs, mediated by stretch receptors via the Vagus nerve (CN X) to the DRG.

Question 1

In the presence of vasopressin, what is the greatest fraction of filtered water absorbed?

Accepted Answer

Proximal tubule

Answer

Loop of Henle

Answer

Distal tubule

Answer

Collecting duct

Question 2

Which parameter best denotes airway resistance?

Accepted Answer

Mid respiratory flow rates

Answer

Vital Capacity

Answer

FEV1

Answer

Total volume

Question 3

What change occurs in blood as it passes through systemic capillaries, EXCEPT for one of the following?

Accepted Answer

Shift of oxygen dissociation curve to the left

Answer

Increase in hematocrit

Answer

pH decreases

Answer

Increase in protein content

Question 4

If pulmonary arterial pressure > alveolar pressure > venous pressure (Pa > Palv > Pv), under normal circumstances, which zone of the lung is being described?

Accepted Answer

Zone II

Answer

Zone I

Answer

Zone III

Answer

Zone IV

Question 5

What reflex is responsible for tachycardia during right ventricle distention?

Accepted Answer

Bainbridge reflex

Answer

Bezold-Jaisch reflex

Answer

Cushing reflex

Answer

J-reflex

Question 6

In an obese patient, what is the most likely respiratory change?

Accepted Answer

Alveolar hypoventilation

Answer

Functional residual capacity (FRC) is unchanged

Answer

Residual volume is decreased

Answer

Normal work of breathing

Question 7

What is true for restrictive lung disease?

Accepted Answer

FEV1/FVC increased, compliance decreased

Answer

FEV1/FVC decreased, compliance normal

Answer

FEV1/FVC increased, compliance increased

Answer

FEV1/FVC decreased, compliance increased

Question 8

Which of the following statements best describes the factors affecting the diffusion of a gas across the respiratory membrane?

Accepted Answer

Diffusion is inversely proportional to the molecular weight of the gas.

Answer

Diffusion is directly proportional to the thickness of the respiratory membrane.

Answer

Diffusion is independent of the lipid-water solubility of the gas.

Answer

Diffusion is directly proportional to the pressure gradient across the membrane.

Question 9

What is the effect of prolonged oxygen therapy?

Accepted Answer

Atelectasis

Answer

Endothelial damage

Answer

Increased pulmonary compliance

Answer

Decreased vital capacity

Question 10

Which nucleus is primarily responsible for the generation of the respiratory rhythm?

Accepted Answer

Pre-Botzinger Complex

Answer

Pneumotaxic centre

Answer

Dorsal group of nucleus

Answer

Apneustic centre

Respiratory System — MCQs

Respiratory System — MCQs

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