Respiration – 2017

✅ Correct Answer: 

7 weeks

• Mycobacterium tuberculosis is a slow-growing organism.
• On Lowenstein–Jensen medium (or other solid culture media), colonies may take up to 6–7 weeks to appear.
• That’s why culture, while being the gold standard for diagnosis, is time-consuming compared to PCR-based molecular tests (e.g., GeneXpert).

❌ Why the Other Options Are Incorrect

• 4 weeks → Colonies can sometimes appear by 3–4 weeks, but culture may take longer, so this is not the maximum time.
• 2 days → Far too short; no visible growth of M. tuberculosis occurs in such a short period.
• 7 days → Early growth is impossible; even rapid liquid culture systems take longer than this.
• 4 days → Same issue; M. tuberculosis has a very slow doubling time (~18–24 hours), unlike most bacteria (20–30 min).

• Atmospheric pressure at sea level = 760 mmHg

• Oxygen makes up about 21% of air → 0.21 × 760 ≈ 160 mmHg (inspired air)

• After humidification and gas exchange in the alveoli, PO₂ drops to about 104 mmHg

✅ Correct Answer:

Acute respiratory distress syndrome (ARDS)

• The classic histological hallmark of ARDS is diffuse alveolar damage (DAD).
• Pathology:
  • Injury to alveolar epithelium and capillary endothelium → leakage of protein-rich fluid.
  • Formation of hyaline membranes (dead cells + fibrin exudate) lining alveoli.
  • Leads to severe impairment in gas exchange, decreased lung compliance, and hypoxemia refractory to oxygen therapy.
• Clinically, ARDS is caused by conditions like sepsis, trauma, pneumonia, aspiration, or shock.

❌ Chronic obstructive pulmonary disease

• COPD includes chronic bronchitis and emphysema.
• Pathology involves airway inflammation and alveolar wall destruction, not diffuse alveolar damage with hyaline membranes.

❌ Transfusion-associated lung injury (TRALI)

• TRALI presents with acute hypoxemia after blood transfusion.
• It can cause non-cardiogenic pulmonary edema, but it is not defined by DAD histologically like ARDS.

❌ Coal workers’ pneumoconiosis

• A type of pneumoconiosis due to inhalation of coal dust.
• Histology shows coal macules and nodules, not diffuse alveolar damage.

❌ Distal acinar emphysema

• A subtype of emphysema, often associated with spontaneous pneumothorax in young adults.

✅ Correct Answer: 

Lower lobes of both lungs

• Bronchiectasis is a chronic condition characterized by permanent dilation of bronchi and bronchioles due to recurrent infections, obstruction, or impaired clearance (e.g., cystic fibrosis, primary ciliary dyskinesia).
• The lower lobes are most affected because:
  • Gravity promotes pooling of secretions here.
  • Impaired clearance in dependent regions predisposes to repeated infection and chronic inflammation.
• Clinically, patients present with chronic productive cough, purulent sputum, recurrent infections, and sometimes hemoptysis.

❌ Middle lobe of the right lung

• The right middle lobe is prone to collapse (middle lobe syndrome) due to its long, narrow bronchus and sharp angle, but this is not the most common site for bronchiectasis overall.

❌ Lower lobe of the right lung

• Incorrect because bronchiectasis commonly affects both lower lobes, not just the right side.

❌ Upper lobe of the left lung

• Upper lobes are less frequently affected.
• However, certain conditions like tuberculosis or aspergillosis preferentially involve the upper lobes.

❌ Upper lobes of both lungs

• Again, upper lobes are not the typical site of bronchiectasis.
• Exceptions occur in cystic fibrosis, where upper lobe involvement is more prominent.

✅ Correct Answer:

Gray hepatization

In lobar pneumonia, the lung progresses through classic stages:

• Congestion → vascular engorgement, alveolar fluid, many bacteria.
• Red hepatization → alveoli filled with RBCs, neutrophils, and fibrin (lung looks red, liver-like consistency).
• Gray hepatization → RBCs begin to disintegrate, neutrophils and fibrin dominate, giving a grayish-brown appearance.
• Resolution → enzymatic digestion of exudate, clearing by macrophages, and return to normal structure.
• Thus, the hallmark of gray hepatization is the breakdown of red cells and persistent fibrin-rich exudate.

❌ Abscess formation

• This is a complication of pneumonia, not a normal stage.
• Caused by tissue necrosis and liquefaction, usually due to virulent organisms (e.g., Staph aureus, Klebsiella).

❌ Red hepatization

• Characterized by intact RBCs, neutrophils, and fibrin → lung appears red and liver-like.
• RBCs have not yet disintegrated here.

❌ Congestion

• The very first stage, showing vascular engorgement, fluid, few neutrophils, many bacteria.
• No exudate breakdown yet.

❌ Resolution

• Final stage → enzymatic digestion and clearance of exudate by macrophages.
• Lung gradually returns to normal appearance.

✅ Correct Answer: 

Superior surface of the first rib

• The scalene tubercle is a small bony ridge on the superior surface of the first rib.
• It serves as the insertion point for the anterior scalene muscle.
• This tubercle also helps divide the subclavian vein (which lies anterior to it) and the subclavian artery (which lies posterior to it).
• Clinically, this is important because it acts as a landmark in the thoracic outlet region.

❌ Inferior surface of the twelfth rib

• The twelfth rib is a floating rib without a scalene attachment.
• No scalene tubercle is found here.

❌ Superior surface of the twelfth rib

• Same reasoning as above — the twelfth rib is not associated with the scalene muscles or a tubercle.

❌ Posterior surface of the first rib

• The scalene tubercle is not posterior; it is on the superior surface of the first rib.

❌ Anterior surface of the tenth rib

• The tenth rib is also not related to the scalene tubercle.
• Scalene tubercle is unique to the first rib.

✅ Correct Answer:

Recurrent laryngeal nerves

• The recurrent laryngeal nerves are branches of the vagus nerves.
• After looping around their respective structures (right around the subclavian artery, left around the aortic arch), they ascend in the tracheoesophageal groove, which is a midline structure at the thoracic inlet.
• This central position makes them especially vulnerable during surgeries involving the thyroid or esophagus.

❌ Phrenic nerve

• Runs along the lateral aspect of the pericardium, between pleura and pericardium.
• Not in the midline, but more lateral at the thoracic inlet.

❌ Thoracic duct

• While it passes through the thoracic inlet, it lies left of the midline, arching laterally to drain into the left venous angle.
• Not strictly central.

❌ None of these

• Incorrect, because a midli

✅ Correct Answer: 

Inferior left ventricular wall

• In a hiatal hernia, the stomach herniates upward through the esophageal hiatus (T10).
• The esophageal hiatus lies posterior to the heart, but anatomically it sits very close to the inferior surface of the left ventricle.
• When the hernia sac enlarges, it pushes against the inferior wall of the left ventricle, which can sometimes impair cardiac function and even be seen as a posterior mediastinal mass on imaging.

❌ Right atrium

• Although the esophagus lies posterior to the heart, the right atrium is more anterior and to the right.
• It is not directly behind the esophagus, so it is less likely to be compressed by a hiatal hernia.

❌ Right phrenic nerve

• Runs along the right side of the pericardium to the diaphragm.
• Not in close relation to the esophageal hiatus, so not the main structure compressed.

❌ Pulmonary artery

• Lies superior and anterior, near the base of the heart.
• Too far away from the esophageal opening to be affected by a hiatal hernia.

❌ Aorta

• Passes through the aortic hiatus at T12, which is separate and posterior to the esophageal hiatus.
• Not compressed by a hiatal hernia.

✅ Correct Answer: 

Beside internal thoracic artery

• Sternal glands are small lymph nodes that lie along the internal thoracic (mammary) artery, usually found near the sternum.
• They are important because they receive lymphatic drainage from the medial part of the breast, anterior thoracic wall, and part of the upper abdominal wall.
• This is clinically relevant in breast cancer spread, where these nodes may become enlarged.

❌ Posterior to intercostal spaces

• The lymph nodes related to intercostal spaces are called intercostal nodes, not sternal glands.

❌ Right to internal jugular vein

• Lymph nodes here are the deep cervical nodes, not the sternal group.

❌ Anterior to thoracic duct

• The thoracic duct runs posteriorly in the mediastinum. The sternal (parasternal) nodes are located much more anteriorly, near the sternum, not related to the thoracic duct.

❌ None of these

• Incorrect, because the correct anatomical relation is well established: sternal glands lie beside the internal thoracic artery.

✅ Correct Answer:

Smoking

• Smoking is the single most important and common cause of COPD worldwide.
• Cigarette smoke triggers chronic airway inflammation, mucus hypersecretion, destruction of alveolar walls (emphysema), and narrowing of small airways (chronic bronchitis).
• Over 80–90% of COPD cases are directly linked to cigarette smoking.

❌ Environmental pollution

• Air pollution (indoor and outdoor) can worsen symptoms and contribute, especially in developing countries (e.g., biomass fuel exposure).
• But it is not the leading cause — smoking is much more significant.

❌ Fibrosis

• Pulmonary fibrosis is a restrictive lung disease, not an obstructive one.
• It reduces lung compliance and diffusion but does not cause COPD.

❌ Aging

• Aging reduces lung elasticity and reserve but does not by itself cause COPD.
• It only increases vulnerability if combined with other risk factors.

❌ Dust

• Occupational dust exposure (coal, silica, cotton) can cause occupational lung diseases (pneumoconiosis), which may lead to obstructive features.
• However, these are much less common compared to smoking-induced COPD.

✅ Correct Answer: 

Trachea

The trachea is not part of the posterior mediastinum.

• The trachea lies in the superior mediastinum and continues into the thorax until its bifurcation at the level of T4–T5 (sternal angle), where it forms the primary bronchi.
• The posterior mediastinum is located behind the pericardium and anterior to the vertebral column, and the trachea does not extend into this region.

❌ Splanchnic nerves

• These nerves (greater, lesser, and least thoracic splanchnic nerves) pass through the posterior mediastinum to reach abdominal ganglia.
• They are therefore structures of the posterior mediastinum.

❌ Thoracic duct

• The thoracic duct, the largest lymphatic channel, ascends through the posterior mediastinum and drains into the junction of the left subclavian and internal jugular veins.

❌ Azygous vein

• The azygous vein ascends along the right side of the vertebral column in the posterior mediastinum and drains into the superior vena cava.

❌ Vagus nerve

• The vagus nerves descend through the thorax, contributing to the esophageal plexus in the posterior mediastinum before continuing into the abdomen.

Correct Answer:
✅ Gives off branch to superior lobe before entering the root of lung

• Explanation: The right pulmonary artery is longer than the left because it passes horizontally across the mediastinum. Before entering the hilum, it gives off a branch to the superior lobe of the right lung (the eparterial branch) — unique because this branch arises before the artery reaches the lung root. The remaining branches enter with the main bronchus at the hilum.

Incorrect Options:

❌ Descend into lung anterolateral to main bronchus

• Wrong. On the right side, the pulmonary artery is positioned anterior to the right main bronchus at the hilum, not anterolateral.

❌ Bifurcate from pulmonary trunk at xiphoid level

• Incorrect. The pulmonary trunk bifurcates at the level of the sternal angle (T4–T5), not at the xiphoid.

❌ Carry oxygenated blood

• False. Pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs.

❌ Goes to opposite lung

• Incorrect. Each pulmonary artery supplies its own lung (right pulmonary artery → right lung).

Correct Answer:
✅ Linea alba

• Explanation: The xiphoid process is the smallest and most inferior part of the sternum. The linea alba, a fibrous midline structure formed by the fusion of aponeuroses of abdominal muscles, attaches to its tip. The diaphragm and rectus abdominis also have connections to the posterior aspect of the xiphoid, but the tip itself serves as the attachment for the linea alba.

Incorrect Options:

❌ Costal cartilages

• They attach to the body of the sternum and extend laterally, not to the tip of the xiphoid process.

❌ Rectus abdominis

• Attaches to the anterior surface of the xiphoid process, not its tip.

❌ None of these

• Incorrect, because linea alba is clearly attached to the tip.

❌ Diaphragm

• Attaches to the posterior aspect of the xiphoid process, not its tip.

Correct Answer:
✅ Vocal cord attaches to posterior surface

• Explanation: The thyroid cartilage is the largest laryngeal cartilage, made of hyaline cartilage. The vocal cords (true vocal folds) do not attach to its posterior surface. Instead, they attach to the inner surface of the thyroid cartilage (anteriorly) at the midline (laryngeal prominence). Posteriorly, the vocal cords are attached to the arytenoid cartilages, not to the thyroid cartilage.

Incorrect Options:

❌ Thyrohyoid membrane connects to its upper border

• Correct. The thyrohyoid membrane stretches between the upper border of the thyroid cartilage and the hyoid bone.

❌ Has oblique line on the posterior surface

• Correct. The oblique line is present on the external surface (side) of the thyroid cartilage, providing attachment for sternothyroid, thyrohyoid, and inferior constrictor muscles.

❌ Largest cartilage

• Correct. The thyroid cartilage is the largest of the laryngeal cartilages.

❌ Hyaline cartilage

• Correct. The thyroid cartilage is composed of hyaline cartilage (though it can ossify with age).

Correct Answer:
✅ Sternum

• Explanation: The anteroposterior diameter of the thoracic cavity increases mainly due to the pump-handle movement of the upper ribs (2–6). When these ribs elevate during inspiration, they push the sternum forward and upward, just like a pump handle. This increases the anteroposterior diameter of the thoracic cage, aiding in lung expansion.

Incorrect Options:

❌ Lower costal lines

• Lower ribs (7–10) move with a bucket-handle movement, increasing the transverse diameter, not the anteroposterior diameter.

❌ Upper costal lines

• While upper ribs are indeed involved, the sternum’s forward movement is the key structure increasing the anteroposterior diameter, not just the ribs themselves.

❌ None of these

• Incorrect, because the sternum is definitely involved.

❌ Diaphragm

• Contraction of the diaphragm increases the vertical diameter of the thoracic cavity, not the anteroposterior one.

Correct Answer:
✅ At birth

• Explanation: The Bacillus Calmette–Guérin (BCG) vaccine is given at birth (or as soon as possible after birth) to protect against tuberculosis (TB), particularly severe forms such as miliary TB and TB meningitis in children. It is a live attenuated vaccine derived from Mycobacterium bovis.

Incorrect Options:

❌ 14 weeks

• At this age, infants typically receive the third doses of DPT, Hepatitis B, Hib, Polio (as per EPI schedule), not BCG.

❌ 6 weeks

• This is when the first doses of DPT, Polio, Hep B, Hib, Rotavirus, Pneumococcal are given.

❌ 2 years

• There is no scheduled BCG dose at this age.

❌ 4 weeks

• At this time, no separate vaccination is scheduled; BCG is already given at birth.

Correct Answer:
✅ Bridge of the nose

• Explanation: The frontonasal prominence contributes to the formation of the forehead, dorsum (bridge) of the nose, and the medial/lateral nasal prominences. These prominences later give rise to specific nasal structures. Thus, the bridge (dorsum) of the nose directly develops from the frontonasal prominence.

Incorrect Options:

❌ The intermaxillary segment

• Derived from the fusion of the two medial nasal prominences, not the frontonasal prominence itself.

❌ Sides of the nose

• Formed by the lateral nasal prominences, which come from the frontonasal prominence secondarily, but the direct structure is the lateral nasal prominence, not the frontonasal prominence as a whole.

❌ The nasal septum

• Formed by the medial nasal prominences, not directly from the frontonasal prominence.

❌ Tip of the nose

• Derived from the medial nasal prominence, not the entire frontonasal prominence.

Correct Answer:
✅ Lumbar vertebrae, costal cartilages, and the sternum

• Explanation: The diaphragm has three main origins:

  • Lumbar vertebrae: via right and left crura (arising from L1–L3).

  • Costal cartilages: from the inner surfaces of ribs 7–12 and their costal cartilages.

  • Sternum: from the posterior aspect of the xiphoid process.
    These fibers converge into the central tendon of the diaphragm.

Incorrect Options:

❌ Pleural membranes, costal cartilages, and the lumbar vertebrae

• The pleura covers the lungs, but does not contribute to the diaphragm’s origin.

❌ Pleural membranes, costal cartilages, and the sternum

• Again, pleura is not a point of origin.

❌ Lumbar vertebrae, pleural membranes, and the sacrum

• The sacrum is far below the diaphragm and unrelated to its origin.

❌ Lumbar vertebrae, sacrum, and the sternum

• The sacrum is not involved in diaphragm attachment.

Correct Answer:
✅ Terminal bronchioles

• Explanation: The respiratory zone is where gas exchange occurs and it begins at the respiratory bronchioles, continuing into the alveolar ducts, alveolar sacs, atria, and alveoli. The terminal bronchioles, however, are the last part of the conducting zone — they only conduct air and do not participate in gas exchange.

Incorrect Options:

❌ Respiratory bronchioles

• These are the first part of the respiratory zone where alveoli begin to bud off.

❌ Alveolar sac

• Part of the respiratory zone, composed of clusters of alveoli.

❌ Alveoli

• The main site of gas exchange; definitely part of the respiratory zone.

❌ Atria

• Openings that connect alveolar ducts to alveolar sacs; part of the respiratory zone.

Correct Answer:
✅ Residual volume

• Explanation: Spirometry measures air volumes that move in and out of the lungs, like tidal volume, inspiratory capacity, expiratory reserve volume, and vital capacity. However, it cannot measure any volume that remains trapped in the lungs after maximal expiration — the residual volume (RV). Since RV cannot be exhaled, it requires special methods (like helium dilution or body plethysmography) to be determined.

Incorrect Options:

❌ Expiratory reserve volume

• Can be measured by spirometry as the extra volume exhaled after normal expiration.

❌ Inspiratory capacity

• Spirometry can measure this (TV + IRV).

❌ Vital capacity

• Measured easily with spirometry (TV + IRV + ERV).

❌ Tidal volume

• Directly measurable by spirometry as the normal breath volume.

Correct Answer:
✅ Tidal volume + inspiratory reserve volume + expiratory reserve volume

• Explanation: Vital capacity (VC) is the maximum volume of air a person can exhale after a maximum inhalation. It includes:

  • Tidal volume (TV): normal breath (~500 mL)

  • Inspiratory reserve volume (IRV): extra air you can inhale after a normal inspiration

  • Expiratory reserve volume (ERV): extra air you can exhale after a normal expiration

VC=TV+IRV+ERV\text{VC} = TV + IRV + ERVVC=TV+IRV+ERV

It does not include residual volume (RV), which is the air that remains in the lungs after maximal exhalation.

Incorrect Options:

❌ Tidal volume + expiratory reserve volume + residual volume

• This includes residual volume, which is not part of vital capacity.

❌ Residual volume + tidal volume + expiratory reserve volume

• Again, residual volume is not counted in vital capacity.

❌ Tidal volume + inspiratory reserve volume

• This represents inspiratory capacity (IC), not vital capacity.

❌ Tidal volume + expiratory reserve volume

• This represents expiratory capacity, not vital capacity.

• During gastrulation (which occurs in the third week of embryonic development), the mesoderm forms between the ectoderm and endoderm.

• Shortly after it forms, the paraxial mesoderm (the part closest to the midline) begins to segment into somites.

• This process — called segmentation or somitogenesis — starts near the cranial end and progresses caudally.

🧬 Timeline:

• Week 3: Mesoderm forms and starts segmenting into somites.

• By end of week 5: About 42–44 pairs of somites have formed.

❌ 7th week

• By this stage, organogenesis is well underway, limb buds are forming, and many somites are already developed. Segmentation started much earlier.

❌ 6th week

• Neural tube is closed, upper limbs show hand plates, and intestines begin herniation — segmentation is already long established.

❌ 4th week

• By the 4th week, segmentation is well advanced, and somites are visible as paired blocks along the neural tube. But the process began earlier in week 3.

❌ 5th week

• Growth and differentiation of structures continues; again, segmentation is not starting here — it has already occurred.

✅ Correct Answer:

Week 16 – Week 26

• The canalicular stage of lung development lasts from 16 to 26 weeks of gestation.
• Key features:
  • Formation of respiratory bronchioles and early alveolar ducts.
  • Lumen of airways becomes larger (“canalized”).
  • Vascularization increases, bringing capillaries close to developing epithelium.
  • By the end of this stage, limited gas exchange becomes possible, so survival outside the womb (though poor) may begin around week 24.

❌ Week 36 – Week 40

• This corresponds to the alveolar stage, when true alveoli form and mature until after birth.

❌ Week 26 – Week 36

• This is the saccular stage, characterized by terminal sacs forming and surfactant production increasing.

❌ Week 6 – Week 16

• This is the pseudoglandular stage, when the lung looks like an exocrine gland and only conducting airways are formed (no gas exchange possible).

❌ Week 4 – Week 8

• This is the embryonic stage, when the lung bud branches into primary, secondary, and tertiary bronchi.

✅ Correct Answer:

Trachea

• The trachea contains C-shaped hyaline cartilage rings.
• These rings keep the airway open and prevent collapse during inspiration.
• The open part of the C-shaped ring faces posteriorly and is bridged by the trachealis muscle, which allows flexibility and adjusts the diameter during coughing.

❌ Respiratory bronchiole

• These are smaller airways, the first part of the respiratory zone.
• They do not contain cartilage; instead, they are supported by smooth muscle and elastic fibers.

❌ Alveolar duct

• Lined by alveoli, with no cartilage.
• They rely on surrounding alveolar walls for structural support.

❌ Alveolar sac

• A cluster of alveoli sharing a common opening.
• No cartilage, purely thin walls specialized for gas exchange.

❌ Alveoli

• Microscopic sacs where gas exchange occurs.
• Composed of type I and type II pneumocytes, elastic fibers, and capillaries — no cartilage.

✅ Correct Answer:

Diabetic ketoacidosis

• Acetone/acidic breath odor (often described as fruity breath) is a classic sign of diabetic ketoacidosis (DKA).
• In DKA, lack of insulin → excessive lipolysis → ketone body formation (acetoacetate, β-hydroxybutyrate, acetone).
• Acetone is volatile and excreted via the lungs, causing the distinctive breath odor.
• Patients usually present with polyuria, dehydration, Kussmaul breathing, and altered mental status.

❌ Diabetic insipidus

• Characterized by polyuria and polydipsia due to ADH deficiency (central) or renal resistance (nephrogenic).
• No ketosis, no fruity breath smell.

❌ Central diabetes

• Refers to central diabetes insipidus (failure of hypothalamus/posterior pituitary to release ADH).
• Again, no ketone production, so no acetone smell.

❌ None of these

• Incorrect, because there is a well-recognized condition (DKA) that causes acetone breath.

❌ Achalasia

• A motility disorder of the esophagus due to failure of the lower esophageal sphincter to relax.
• Presents with dysphagia, regurgitation, and chest pain — but not fruity breath odor.

✅ Correct Answer: 

Myeloperoxidase

• Azurophilic granules (also called primary granules) are found in neutrophils.
• They contain myeloperoxidase (MPO), which plays a central role in the respiratory burst by generating hypochlorous acid (HOCl) from hydrogen peroxide and chloride → powerful bactericidal effect.
• These granules also contain defensins, acid hydrolases, and other antimicrobial enzymes, but MPO is the classic marker.

❌ Alkaline phosphatase

• Found in specific (secondary) granules, not in azurophilic granules.
• Used in lab tests (e.g., leukocyte alkaline phosphatase score).

❌ Collagenase

• Present in specific (secondary) granules of neutrophils, helps break down collagen during tissue invasion.
• Not in azurophilic granules.

❌ Hydrolase

• Lysosomal hydrolases are found in various lysosomes and granules, but in neutrophils, the key enzyme of azurophilic granules is MPO, which is more specific.

❌ Collagen

• Collagen is a structural protein of connective tissue, not an enzyme or a granule component.

✅ Correct Answer:

Inhaled corticosteroid

• Inhaled corticosteroids (e.g., budesonide, fluticasone) are the mainstay of long-term asthma management.
• They reduce airway inflammation, decrease hyperresponsiveness, and lower the frequency of exacerbations.
• Because they act locally in the lungs, systemic side effects are much less than with oral corticosteroids.

❌ Oral corticosteroid

• Oral corticosteroids (e.g., prednisone) are used only for severe acute exacerbations or poorly controlled asthma, not for regular maintenance because of significant systemic side effects.
• So, not the “main” drug of choice.

❌ None of these

• Incorrect, because inhaled corticosteroids are clearly effective and widely used for asthma.

❌ Pilocarpine

• Pilocarpine is a muscarinic agonist.
• It increases bronchoconstriction and secretions → worsens asthma instead of treating it.

❌ Sildenafil

• Sildenafil is a PDE-5 inhibitor used in erectile dysfunction and pulmonary hypertension, not in asthma.

✅ Correct Answer:

Increase heart contraction

• At low doses, epinephrine predominantly stimulates β₁-adrenergic receptors in the heart.
• This leads to:
  • ↑ Heart rate (positive chronotropy)
  • ↑ Force of contraction (positive inotropy)
• These β effects dominate at low concentrations before α₁-mediated effects (like vasoconstriction and pupil dilation) take over at higher doses.

❌ Increased gut motility

• Epinephrine actually decreases gut motility (sympathetic effect) through α and β receptor activation.
• The sympathetic nervous system slows digestion, not enhances it.

❌ Pupil constriction

• Pupil constriction (miosis) is a parasympathetic action via the oculomotor nerve (CN III).
• Epinephrine, being adrenergic, does the opposite.

❌ Salivary secretion

• Parasympathetic activity causes watery salivation.
• Epinephrine may produce thicker, viscous secretions, but it is not the main effect at low doses.

❌ Pupil dilation

• Epinephrine causes mydriasis (pupil dilation) through α₁ receptor stimulation.
• However, this is more evident at higher doses, not at low doses where β effects dominate.

✅ Correct Answer:

Pilocarpine

• Pilocarpine is a direct-acting cholinergic agonist (muscarinic receptor agonist).
• It mimics acetylcholine by binding directly to muscarinic receptors.
• Clinically, it is used in glaucoma (contracts ciliary muscle, increases aqueous humor outflow) and xerostomia (dry mouth) because it stimulates salivation.
• Key: Direct-acting agents bind to cholinergic receptors themselves, unlike indirect-acting drugs that inhibit acetylcholinesterase.

❌ Organophosphorous

• These are irreversible acetylcholinesterase inhibitors.
• They prevent breakdown of acetylcholine, causing excessive stimulation of cholinergic receptors.
• Thus, they are indirect-acting, not direct-acting.

❌ Physostigmine

• A reversible acetylcholinesterase inhibitor.
• Increases acetylcholine at synapses → indirect-acting.
• Used in atropine poisoning and glaucoma.

❌ None of these

• Wrong, because a valid direct-acting agonist (pilocarpine) is listed.

❌ Neostigmine

• Another reversible acetylcholinesterase inhibitor.
• Indirect-acting, used in myasthenia gravis and to reverse neuromuscular blockade.

✅ Correct Answer:

Intercostal nerve

The parietal pleura (the membrane lining the thoracic wall, diaphragm, and mediastinum) is richly supplied by somatic sensory nerves.

• The costal pleura and peripheral parts of the diaphragmatic pleura receive innervation from intercostal nerves → sharp, localized pain when irritated (like during a needle insertion).
• That is why the patient feels pain during pleural tapping (thoracentesis).

❌ Recurrent laryngeal nerve

• This nerve is a branch of the vagus nerve.
• It supplies the intrinsic muscles of the larynx (except cricothyroid) and sensation below the vocal cords.
• It has no role in innervating the pleura.

❌ Phrenic nerve

• The phrenic nerve supplies the central part of the diaphragmatic pleura and mediastinal pleura.
• Pain here is often referred to the shoulder (C3–C5 dermatomes).
• But in this case, the needle pierces costal pleura, which is supplied by intercostal nerves, not the phrenic.

❌ None of these

• Incorrect, because the pleura is sensory innervated by specific nerves (intercostal & phrenic), so it cannot be “none.”

❌ Vagus nerve

• The vagus nerve provides parasympathetic fibers to thoracic and abdominal viscera.
• It does not supply pain sensation to the pleura.

Correct Answer:
✅ Type 2 alveolar epithelial cells

• Explanation: Type II pneumocytes (alveolar epithelial cells) are cuboidal cells found in the alveoli. They secrete pulmonary surfactant, a phospholipid-rich substance (mainly dipalmitoyl phosphatidylcholine) that reduces surface tension and prevents alveolar collapse at the end of expiration. They also serve as progenitor cells, capable of dividing and differentiating into Type I cells after lung injury.

Incorrect Options:

❌ Squamous epithelial cells of trachea

• These are part of the tracheal lining in abnormal/pathological states (normally pseudostratified ciliated epithelium), and they do not produce surfactant.

❌ Type 1 alveolar epithelial cells

• Flattened cells that cover ~95% of the alveolar surface area; their main role is gas exchange, not surfactant production.

❌ Endothelial cells

• Line pulmonary capillaries; their role is in gas exchange and barrier function, not surfactant secretion.

❌ Secretory cells

• Generic term, but surfactant is specifically secreted by Type II pneumocytes, not a general secretory cell population.

Correct Answer:
✅ They are columnar cells with microvilli at the apical surface

• Explanation: Brush cells are specialized columnar epithelial cells found in the respiratory tract epithelium. They are characterized by short, blunt microvilli on their apical surface, which likely function in sensory reception or chemoreception. These cells make contact with afferent nerve endings and may help detect changes in the chemical composition of the airway.

Incorrect Options:

❌ They are columnar cells with microvilli at the lateral surface

• Incorrect, because microvilli are confined to the apical surface, not the lateral sides.

❌ They are cuboidal cells with microvilli at the apical surface

• Wrong, brush cells are columnar, not cuboidal.

❌ They are squamous cells with microvilli at the apical surface

• Squamous cells are flat and thin, not the brush cell type.

❌ They are cuboidal cells with microvilli at the basal surface

• Incorrect, as microvilli are never found on the basal surface — only the apical surface.

Correct Answer:
✅ Emphysema

• Explanation: In emphysema (a type of COPD), there is permanent enlargement of airspaces due to destruction of alveolar walls. The trapped air causes hyperinflation of the lungs, which increases the anteroposterior diameter of the chest. This produces the classic “barrel-shaped chest” appearance. Many textbooks describe this deformity as a “pigeon-shaped” or “barrel chest” in emphysema patients. It is a hallmark of long-standing emphysema.

Incorrect Options:

❌ Chronic bronchitis

• Presents with a productive cough (“blue bloater”), but chest deformity is not typical.

❌ Acute bronchitis

• Short-term inflammation of bronchi with cough and sputum; does not cause chronic chest shape changes.

❌ Tuberculosis

• Causes cavitation, fibrosis, and weight loss but not pigeon/barrel chest deformity.

❌ Asthma

• Leads to episodic airway obstruction and hyperinflation during attacks, but long-term pigeon/barrel chest is not characteristic.

Correct Answer:
✅ 7 mmHg

• Explanation: The pulmonary capillary pressure (also called pulmonary capillary hydrostatic pressure) is normally around 7 mmHg. This low pressure is essential to prevent pulmonary edema, since fluid balance across the pulmonary capillaries depends on Starling forces. In contrast, systemic capillary pressure is much higher (~25 mmHg). The low pulmonary pressure allows efficient gas exchange without fluid leakage.

Incorrect Options:

❌ 100 mmHg

• This is closer to systemic arterial pressure (systolic), not capillary pressure.

❌ 75 mmHg

• Approximate mean systemic arterial pressure, not pulmonary capillary pressure.

❌ 2 mmHg

• Too low; this is more in line with right atrial pressure (central venous pressure).

❌ 5 mmHg

• Closer, but slightly lower than the actual normal pulmonary capillary pressure (≈7 mmHg).

Correct Answer:
✅ Serratus anterior

• Explanation: The intrinsic muscles of respiration are those directly involved in breathing and located within the thoracic wall itself — primarily the diaphragm, external intercostals, and internal intercostals. The serratus anterior is mainly a muscle of the upper limb (protracts and stabilizes the scapula) and plays only an accessory role in respiration when the shoulder girdle is fixed. Thus, it is not considered an intrinsic respiratory muscle.

Incorrect Options:

❌ Internal intercostal

• An intrinsic muscle of respiration. It assists in forced expiration by depressing the ribs.

❌ External intercostal

• Another intrinsic respiratory muscle. It assists in inspiration by elevating the ribs.

❌ None of these

• Incorrect, because one option (serratus anterior) is clearly not intrinsic.

❌ Diaphragm

• The principal muscle of respiration and intrinsic to the respiratory system. It contracts to increase thoracic volume during inspiration.

Correct Answer:
✅ Dipalmitoyl phosphatidylcholine

• Explanation: The major component of pulmonary surfactant is dipalmitoyl phosphatidylcholine (DPPC), also called lecithin. Surfactant is secreted by type II pneumocytes and functions to reduce surface tension within alveoli, preventing their collapse during expiration. Adequate surfactant production begins around 24 weeks of gestation but becomes sufficient only after 34–36 weeks. Deficiency leads to neonatal respiratory distress syndrome (NRDS).

Incorrect Options:

❌ Phosphatidyl lecithin

• This is a broader term, but the specific surfactant component is dipalmitoyl phosphatidylcholine, not generic lecithin.

❌ None of these

• Incorrect, because DPPC is indeed the right answer.

❌ Gangliosides

• Glycolipids present in neuronal cell membranes, not involved in surfactant function.

❌ Cerebrosides

• Another type of glycolipid, important in myelin sheath structure, not lung surfactant.

Correct Answer:
✅ Symphysis

• Explanation: The joints between the bodies of adjacent vertebrae are secondary cartilaginous joints (symphyses). Each is formed by a thin layer of hyaline cartilage covering the vertebral bodies, with the intervertebral disc (containing the nucleus pulposus and annulus fibrosus) in between. These joints allow limited movement but provide strong support and shock absorption.

Incorrect Options:

❌ Cartilaginous

• Too broad. Both synchondrosis and symphysis are types of cartilaginous joints. We need the specific type here.

❌ Synchondrosis

• A primary cartilaginous joint, where bones are united by hyaline cartilage (e.g., epiphyseal plates, first costochondral joint). Intervertebral joints are secondary cartilaginous (symphyses), not primary.

❌ Synovial

• These allow free movement (e.g., shoulder, knee). The intervertebral discs are not synovial joints, although the facet joints (between articular processes of vertebrae) are synovial.

❌ Pivot

• A subtype of synovial joint allowing rotation (e.g., atlantoaxial joint between C1 and C2). Not between vertebral bodies.

Correct Answer:
✅ Pilocarpine

• Explanation: Pilocarpine is a muscarinic cholinergic agonist, meaning it stimulates parasympathetic activity (rest-and-digest), not sympathetic. It is used clinically in the treatment of glaucoma and xerostomia because it increases salivation and causes pupillary constriction (miosis).

Incorrect Options:

❌ Norepinephrine

• Primary neurotransmitter of the sympathetic nervous system; increases heart rate, blood pressure, and causes vasoconstriction.

❌ None of these

• Incorrect, because one option (pilocarpine) clearly does not increase sympathetic activity.

❌ Phenylephrine

• A selective α1-adrenergic agonist; increases sympathetic activity by causing vasoconstriction and raising blood pressure.

❌ Epinephrine

• Secreted by the adrenal medulla, it stimulates both α- and β-adrenergic receptors, strongly increasing sympathetic effects (increased HR, bronchodilation, vasoconstriction/vasodilation depending on receptor).

Correct Answer:
✅ Heart

• Explanation: The heart is located in the middle mediastinum, not the superior mediastinum. The superior mediastinum lies above a horizontal plane drawn from the sternal angle to the T4–T5 vertebral level, and it contains great vessels, the trachea, esophagus, thymus, and nerves. The heart itself sits below this plane, enclosed in the pericardium.

Incorrect Options:

❌ Brachiocephalic vein

• Present in the superior mediastinum. It drains blood from the head, neck, and upper limbs into the superior vena cava.

❌ Superior vena cava

• The upper part of the SVC is in the superior mediastinum, before it enters the right atrium in the middle mediastinum.

❌ Arch of the aorta

• Definitely a structure of the superior mediastinum, giving rise to its three branches.

❌ Subclavian artery

• The origin of the subclavian artery (from the arch of aorta or brachiocephalic trunk) lies in the superior mediastinum.

Correct Answer:
✅ Pleura

• Explanation: The pleura is the serous membrane that covers the lungs. It has two layers:

  • Visceral pleura → directly covers the lung surface.

  • Parietal pleura → lines the thoracic cavity, diaphragm, and mediastinum.
    The pleura reduces friction during breathing and creates a pressure gradient essential for lung expansion.

Incorrect Options:

❌ None of these

• Incorrect, because there is a specific serous membrane for the lungs — the pleura.

❌ Mesothelium

• This refers to the cell type (simple squamous epithelium) that lines serous membranes like pleura, pericardium, and peritoneum, but it is not the name of the membrane itself.

❌ Pericardium

• The serous membrane covering the heart, not the lungs.

❌ Epithelium

• Too general. The pleura is lined by epithelium (mesothelium), but “epithelium” alone does not name the lung’s serous covering.