Comparative Respiratory System — MCQs
Transection at mid-pons level with intact vagus results in:
Which vitamin deficiency is associated with night blindness?
The transport of CO2 in the blood is primarily influenced by which of the following factors?
What is the total surface area of the respiratory membrane in a healthy adult human?
All of the following statements about acid-base disorders are true, EXCEPT:
Which of the following factors contributes to increased airway resistance?
Transection at the mid-pons level results in:
Which among the following has the highest airway resistance?
Which one of the following tests should be applied to compare mean haemoglobin level of two groups of antenatal mothers?
The lungs are derived from an out-pouching of the primitive foregut during which period of intrauterine life?
Comparative Respiratory System Indian Medical PG Practice Questions and MCQs
Question 1: Transection at mid-pons level with intact vagus results in:
- A. Apneusis
- B. Hyperventilation
- C. Irregular shallow breathing
- D. Deep and slow breathing (Correct Answer)
Explanation: ***Deep and slow breathing*** - A transection at the **mid-pons level** disconnects the **pneumotaxic center** from the medullary respiratory centers, while the **vagus nerves remain intact**. - Without the inhibitory input from the pneumotaxic center, inspirations become deep and prolonged due to the unopposed effect of the **apneustic center**, but the intact vagus still provides some inspiratory off-switch, preventing full apneusis. This leads to **deep and slow breathing**. *Apneusis* - **Apneusis**, characterized by prolonged inspiratory gasps, occurs when both the **pneumotaxic center and vagal afferents** (from lung stretch receptors) are non-functional or cut. - In this scenario, the vagus nerves are intact, providing an inspiratory off-switch that prevents the full development of apneusis. *Hyperventilation* - **Hyperventilation** typically results from metabolic acidosis, hypoxemia, or anxiety, leading to an increased rate and depth of breathing. - A mid-pons transection primarily affects the rhythm and duration of inspiration, not necessarily increasing the overall minute ventilation in a compensatory manner. *Irregular shallow breathing* - **Irregular shallow breathing** can be seen with damage to the **medullary respiratory centers** or severe respiratory muscle weakness. - The transection described primarily impacts the integration of pontine and medullary control, particularly the interaction between the apneustic and pneumotaxic centers, leading to deep and slow breaths, not shallow ones.
Question 2: Which vitamin deficiency is associated with night blindness?
- A. Biotin
- B. Vit. A (Correct Answer)
- C. Thiamine
- D. Riboflavin
Explanation: ***Vitamin A*** - **Vitamin A deficiency is THE classic cause of night blindness (nyctalopia)**, one of the earliest signs of deficiency - Vitamin A is essential for synthesis of **rhodopsin**, the photopigment in retinal rod cells responsible for vision in dim light - Deficiency leads to impaired dark adaptation and progressive loss of night vision - Other manifestations include **xerophthalmia, Bitot's spots, and keratomalacia** - This is a high-yield fact for NEET-PG examinations *Riboflavin (Vitamin B2)* - Riboflavin deficiency causes **oral-ocular-genital syndrome** - Clinical features include **angular stomatitis, cheilosis, glossitis, seborrheic dermatitis** - Eye manifestations include **corneal vascularization and photophobia**, NOT night blindness - Does NOT cause night blindness as a primary symptom *Thiamine (Vitamin B1)* - Thiamine deficiency causes **Beriberi** (wet and dry forms) and **Wernicke-Korsakoff syndrome** - Characterized by peripheral neuropathy, cardiac dysfunction, and CNS manifestations - Does NOT cause night blindness *Biotin (Vitamin B7)* - Biotin deficiency is rare and causes **dermatitis, alopecia, conjunctivitis** - Also causes neurological symptoms in severe deficiency - Does NOT cause night blindness
Question 3: The transport of CO2 in the blood is primarily influenced by which of the following factors?
- A. Binding to hemoglobin as carbaminohemoglobin
- B. Conversion to bicarbonate ions by carbonic anhydrase (Correct Answer)
- C. Transport as carbonic acid in red blood cells
- D. Direct dissolution in blood plasma
Explanation: ***Conversion to bicarbonate ions by carbonic anhydrase*** - This is the **primary mechanism** for CO2 transport, accounting for approximately **70%** of total CO2 transport in blood. - Inside red blood cells, CO2 combines with water to form carbonic acid (H2CO3), catalyzed by the enzyme **carbonic anhydrase**. - Carbonic acid **immediately dissociates** into hydrogen ions (H+) and **bicarbonate ions (HCO3-)**. - Bicarbonate ions then diffuse into plasma in exchange for chloride ions (chloride shift), making this the most quantitatively significant transport mechanism. - **Carbonic anhydrase** is the key enzyme that influences this process by accelerating the reaction by approximately **5000-fold**. *Binding to hemoglobin as carbaminohemoglobin* - Approximately **20-23%** of CO2 is transported by directly binding to amino groups on hemoglobin to form **carbaminohemoglobin**. - This is significant but less than bicarbonate transport. - Deoxygenated hemoglobin binds CO2 more readily than oxygenated hemoglobin (Haldane effect). *Transport as carbonic acid in red blood cells* - This is **not correct** because carbonic acid (H2CO3) is only a **transient intermediate** that exists momentarily. - It immediately dissociates into H+ and HCO3-, so CO2 is not actually transported "as carbonic acid" but rather as **bicarbonate ions**. - The carbonic acid step is part of the mechanism, but bicarbonate is the actual transport form. *Direct dissolution in blood plasma* - Only about **7-10%** of CO2 is transported dissolved directly in plasma. - CO2 has limited solubility in plasma, making this the least significant mechanism. - This dissolved CO2 contributes to the partial pressure of CO2 (PCO2) in blood.
Question 4: What is the total surface area of the respiratory membrane in a healthy adult human?
- A. 30 m2
- B. 50 m2
- C. 75 m2 (Correct Answer)
- D. 100 m2
Explanation: ***75 m²*** - The **total surface area** of the respiratory membrane in a healthy adult human is approximately **70-80 m²**, with 75 m² being the most accurate estimate among the given options. - This large surface area is primarily attributed to the presence of approximately **300-500 million alveoli**, which are crucial for efficient gas exchange. - Modern measurements using **stereological techniques** have refined earlier estimates and established this range as the current standard. *100 m²* - This value represents an **older estimate** that has been revised downward with more accurate measurement techniques. - While historically cited in older textbooks, current physiological data supports a **smaller surface area** of approximately 70-80 m². *30 m²* - This value is significantly **underestimated** for the total respiratory membrane surface area. - Such a small surface area would result in highly **inefficient gas exchange**, leading to severe respiratory compromise and inability to meet metabolic demands. *50 m²* - While larger than 30 m², this is still an **underestimation** of the full respiratory membrane surface area. - It does not adequately account for the extensive and intricate branching of the **respiratory bronchioles** and the vast number of alveolar sacs.
Question 5: All of the following statements about acid-base disorders are true, EXCEPT:
- A. Metabolic acidosis is compensated by increasing Pco2 (Correct Answer)
- B. Buffering may be intra & extra cellular
- C. pH determined by Pco2 and HCO3
- D. Respiratory acidosis is compensated by HCO3
Explanation: ***Metabolic acidosis is compensated by increasing Pco2*** - In **metabolic acidosis**, the primary problem is a decrease in **bicarbonate (HCO3-)**. - The compensatory response is **respiratory**, involving an increase in **respiratory rate** and depth to **decrease Pco2**, thereby *raising* the pH back towards normal. Increasing Pco2 would worsen the acidosis. *Buffering may be intra & extra cellular* - **Buffering systems** operate both **intracellularly** (e.g., proteins, phosphates) and **extracellularly** (e.g., bicarbonate-carbonic acid system, hemoglobin). - This dual buffering ensures a rapid and widespread response to changes in acid-base balance throughout the body. *pH determined by Pco2 and HCO3* - According to the **Henderson-Hasselbalch equation**, pH is directly proportional to the ratio of **bicarbonate (HCO3-)** to **Pco2**. - This means that changes in either Pco2 (respiratory component) or HCO3- (metabolic component) will directly influence the overall pH of the blood. *Respiratory acidosis is compensated by HCO3* - In **respiratory acidosis**, the primary problem is an increase in **Pco2** due to hypoventilation. - The compensatory response is **renal**, involving increased reabsorption of **bicarbonate (HCO3-)** and increased excretion of H+ ions to buffer the excess acid.
Question 6: Which of the following factors contributes to increased airway resistance?
- A. Forced expiration
- B. Denser air
- C. High lung volume
- D. Low lung volume (Correct Answer)
Explanation: ***Low lung volume*** - At **low lung volumes**, the radial traction on the airways by the surrounding lung tissue is significantly reduced, leading to **narrowing of the small airways**. - This **decreased airway caliber** directly increases resistance to airflow, making breathing more difficult. - This is the **most physiologically significant factor** affecting airway resistance in normal breathing and clinical conditions. *Forced expiration* - While **forced expiration** can transiently increase airway resistance in certain conditions (e.g., in patients with obstructive lung disease due to dynamic airway compression), it is not a fundamental factor that increases resistance in healthy airways. - The primary mechanism of increased resistance during forced expiration in disease states is due to the **collapse of compliant airways** under positive intrathoracic pressure. *Denser air* - Breathing **denser air** (e.g., at sea level vs. high altitude, or in hyperbaric conditions) does increase resistance, particularly in **turbulent flow** conditions in larger airways. - However, this effect is **relatively minor** compared to the dramatic changes in resistance caused by lung volume variations. - In clinical practice and normal physiology, **lung volume is the predominant variable** affecting airway resistance. *High lung volume* - At **high lung volumes**, the airways are pulled open by increased radial traction from the surrounding lung parenchyma, which actually **decreases airway resistance**. - This wider airway diameter facilitates easier airflow, thereby reducing the effort required for ventilation.
Question 7: Transection at the mid-pons level results in:
- A. Complete cessation of airflow
- B. Increased respiratory rate and depth
- C. Sustained inspiratory phase followed by quick expiration
- D. Prolonged inspiratory phase (Correct Answer)
Explanation: ***Prolonged inspiratory phase*** - Transection at the mid-pons isolates the **apneustic center** from the **pneumotaxic center**, leading to an unopposed inspiratory drive. - This results in **apneusis**, characterized by prolonged, gasping inspirations with brief expirations. - The pneumotaxic center normally limits inspiration; without it, the apneustic center's excitatory effect on the dorsal respiratory group is unopposed. *Complete cessation of airflow* - This typically occurs with transections that damage the **medullary respiratory centers** (ventral and dorsal respiratory groups) or their efferent connections. - A mid-pons transection primarily disrupts regulatory inputs to the medullary centers, rather than abolishing their fundamental activity. *Increased respiratory rate and depth* - This pattern is often associated with conditions like **metabolic acidosis** (Kussmaul breathing) or direct stimulation of the respiratory centers. - A mid-pons transection disrupts rhythmic breathing rather than enhancing it in a coordinated manner. *Sustained inspiratory phase followed by quick expiration* - While apneusis involves a sustained inspiratory phase, the expiration following it is typically brief but not necessarily "quick" in the sense of being forceful. - This option doesn't fully capture the characteristic pattern of apneusis, where the primary abnormality is the prolonged inspiration itself.
Question 8: Which among the following has the highest airway resistance?
- A. Alveolar duct
- B. Respiratory bronchioles
- C. Bronchi (Correct Answer)
- D. Small bronchioles
Explanation: ***Bronchi (Medium-sized bronchi)*** - The **medium-sized bronchi** (approximately 4th-8th generation airways) contribute the **highest proportion to total airway resistance** in the tracheobronchial tree. - At this level, airways are still relatively **narrow** but arranged more in **series** rather than parallel, concentrating resistance. - This is the point of **maximum resistance** before the extensive branching of smaller airways creates parallel pathways. - Accounts for approximately **40-50% of total airway resistance** during normal breathing. *Small bronchioles* - While individual small bronchioles (<1 mm diameter) have narrow lumens, they branch extensively into **thousands of parallel airways**. - This creates an **enormous total cross-sectional area** (up to 20x larger than trachea), which dramatically **reduces total resistance**. - According to principles of parallel resistance, total resistance decreases as more parallel pathways are added: 1/R_total = 1/R₁ + 1/R₂ + ... + 1/Rₙ - Despite small individual diameter, collective parallel arrangement makes them **low resistance** pathways. *Alveolar ducts* - Have the **largest cumulative cross-sectional area** in the entire respiratory system. - Airflow velocity is minimal and flow is entirely **laminar**, offering negligible resistance. - These are part of the respiratory zone where gas exchange occurs primarily by diffusion. *Respiratory bronchioles* - Part of the **transitional/respiratory zone** with extensive branching and large total cross-sectional area. - Offer very low resistance due to their **parallel arrangement** and slow airflow velocity. - Contribute minimally to total airway resistance.
Question 9: Which one of the following tests should be applied to compare mean haemoglobin level of two groups of antenatal mothers?
- A. Analysis of variance
- B. Chi-square test
- C. Unpaired t-test (Correct Answer)
- D. Paired t-test
Explanation: ***Unpaired t-Test*** - The **unpaired t-test** is used to compare the means of **two independent groups** on a continuous variable, such as hemoglobin levels. - Antenatal mothers in two distinct groups are independent, and **hemoglobin level is a continuous variable**, making this the appropriate choice. *Analysis of variance* - **ANOVA** (Analysis of Variance) is used to compare the means of **three or more independent groups**. - Since there are only **two groups** being compared, ANOVA is not the most efficient or appropriate test. *Chi-square test* - The **Chi-square test** is used to analyze the association between **two categorical variables**. - Hemoglobin level is a **continuous variable**, not categorical, so this test is not suitable for comparing means. *Paired t-test* - The **paired t-test** is used to compare the means of **two related groups** or the same group measured at two different times (e.g., before and after an intervention). - The two groups of antenatal mothers are **independent**, not paired or related.
Question 10: The lungs are derived from an out-pouching of the primitive foregut during which period of intrauterine life?
- A. 3rd week
- B. 5th week
- C. 4th week (Correct Answer)
- D. 6th week
Explanation: ***4th week*** - The **respiratory diverticulum (lung bud)** appears as a ventral out-pouching from the **primitive foregut** at approximately **26-28 days** of development, which falls in the **4th week** of intrauterine life [1]. - This marks the beginning of the respiratory system's development, initiating the formation of the **larynx**, **trachea**, **bronchi**, and **lungs** [1]. - The lung bud forms from the foregut endoderm and subsequently divides into the **right and left bronchial buds**. *3rd week* - During the third week, **gastrulation** occurs with the formation of the three germ layers (ectoderm, mesoderm, endoderm). - The **primitive gut tube** begins to form toward the end of the third week through **lateral and cranio-caudal folding**, but the respiratory diverticulum has not yet appeared. - The lung bud out-pouching occurs later, around day 26-28 of the fourth week. *5th week* - By the fifth week, the **laryngotracheal tube** has separated from the foregut via the **tracheoesophageal septum**. - The main **bronchi** continue to elongate and branch into **secondary (lobar) bronchi**. - The initial formation of the lung bud precedes this developmental stage. *6th week* - By the sixth week, the **bronchial tree** undergoes further branching with the formation of **tertiary (segmental) bronchi**. - The **pseudoglandular stage** of lung development is underway, with continued airway differentiation. - This represents a later stage of respiratory development, well after the initial lung bud formation [1].
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