Respiratory System — Set 2

Correct Answer: B. Medulla oblongata

• **Medulla oblongata** = The medulla contains the dorsal respiratory group (DRG), which drives inspiratory neurons, and the ventral respiratory group (VRG), which controls both inspiration and forced expiration, together generating the basic breathing rhythm. • **Continuous autonomic control** — The medullary centres fire rhythmically even in the absence of conscious input, ensuring breathing continues during sleep, anaesthesia, and coma as long as the brainstem is intact. • The pons works with the medulla to smooth and refine the rhythm; the apneustic and pneumotaxic centres in the pons prevent over-inflation of the lungs. • 💡 Option A (Cerebrum) is wrong because the cerebrum handles voluntary, conscious functions such as voluntary breath-holding but does not generate the automatic breathing rhythm; Option C (Cerebellum) is wrong because the cerebellum coordinates motor movements and balance, not autonomic respiratory control; Option D (Hypothalamus) is wrong because the hypothalamus regulates body temperature, hunger, and hormonal balance, not the breathing rhythm.

Correct Answer: B. Silicosis

• **Silicosis** = Silicosis is a progressive and irreversible occupational lung fibrosis caused by chronic inhalation of crystalline silica dust, common in mining, stone cutting, sandblasting, and quarrying. • **Inflammation → fibrosis** — Inhaled silica particles are engulfed by macrophages which die and release enzymes, triggering sustained inflammation and ultimately scar tissue (fibrosis) that permanently stiffens the lungs. • There is no cure; prevention via dust suppression and respirator use is critical, as even after exposure stops the disease can progress. • 💡 Option A (Asthma) is wrong because asthma is primarily an allergic or genetic condition causing reversible bronchoconstriction, not occupational dust fibrosis; Option C (Pneumonia) is wrong because pneumonia is an acute infectious inflammation of the alveoli caused by bacteria, viruses, or fungi; Option D (Emphysema) is wrong because emphysema is caused predominantly by cigarette smoking that destroys alveolar walls, not by occupational silica dust.

Correct Answer: A. It moves downwards and inwards

• **Downward and inward movement** = During passive (quiet) expiration, the external intercostal muscles relax, allowing gravity and the elastic recoil of the lungs and chest wall to pull the ribs downward and inward. • **Volume decrease drives exhalation** — This inward movement shrinks thoracic volume, raises intrapulmonary pressure above atmospheric pressure, and forces air out of the lungs without any active muscular effort. • During forced expiration (e.g., coughing or exercising), the internal intercostal muscles and abdominal muscles actively contract to accelerate rib cage depression. • 💡 Option B (Expands in all directions) is wrong because expansion occurs during inspiration, not expiration; Option C (Remains stationary) is wrong because the rib cage actively moves with every breath, including during normal tidal breathing; Option D (Moves upwards and outwards) is wrong because upward and outward rib movement characterises inspiration when the external intercostals contract.

Correct Answer: B. 70%

• **70% as bicarbonate ions** = Inside red blood cells, the enzyme carbonic anhydrase rapidly catalyses the reaction CO2 + H2O → H2CO3 → H⁺ + HCO3⁻; the bicarbonate ions then diffuse into plasma for transport. • **Chloride shift balances charges** — As HCO3⁻ leaves the red cell, Cl⁻ enters to maintain electrical neutrality — a process called the chloride (Hamburger) shift that sustains efficient bicarbonate transport. • This pathway is the body's primary CO2-transport mechanism and also buffers blood pH, since bicarbonate is a key component of the carbonate buffer system. • 💡 Option A (95%) is wrong because no single transport mechanism accounts for 95% of CO2 carriage; Option C (23%) is wrong because that figure represents CO2 carried bound to haemoglobin as carbaminohaemoglobin; Option D (7%) is wrong because only about 7% of CO2 is simply dissolved directly in plasma, which is the least efficient of the three transport methods.

Correct Answer: A. Trachea

• **Trachea** = The trachea (windpipe) is reinforced by 16–20 C-shaped rings of hyaline cartilage stacked along its length that prevent it from collapsing during the negative pressure of inhalation. • **Why C-shaped and not circular** — The rings are incomplete at the posterior side where the trachea lies against the oesophagus; the gap is bridged by a smooth muscle band (trachealis) that allows the oesophagus to bulge into the trachea's space when a large food bolus is swallowed. • The cartilage rings are palpable in the neck and serve as anatomical landmarks for procedures such as tracheotomy. • 💡 Option B (Pharynx) is wrong because the pharynx is a muscular tube with no cartilaginous rings; Option C (Alveoli) is wrong because alveoli are thin elastic air sacs with no cartilage at all; Option D (Esophagus) is wrong because the oesophagus is part of the digestive system and has only muscular walls — cartilage rings are exclusively a feature of the conducting airways.

Correct Answer: A. Bronchitis

• **Bronchitis** = Bronchitis is the inflammation of the bronchial tube lining, which swells, narrows the airway, and triggers excessive mucus production, resulting in a persistent productive cough. • **Acute vs. chronic forms** — Acute bronchitis usually follows a viral upper respiratory infection and resolves within 2–3 weeks; chronic bronchitis is defined as a productive cough for at least 3 months in each of 2 consecutive years and is a component of COPD, strongly linked to cigarette smoking. • Cilia in the bronchial lining are damaged by inflammation, impairing mucus clearance and raising infection risk. • 💡 Option B (Laryngitis) is wrong because laryngitis is inflammation of the larynx (voice box), causing hoarseness or voice loss; Option C (Sinusitis) is wrong because sinusitis is inflammation of the paranasal sinuses, producing facial pain and congestion; Option D (Rhinitis) is wrong because rhinitis is inflammation of the nasal mucosa, causing a runny or blocked nose.

Correct Answer: C. Tidal Volume

• **Tidal Volume** = Tidal volume is the amount of air that flows in and out of the lungs during a single, effortless resting breath, reflecting the minimum ventilation needed to maintain normal blood gas levels. • **About 500 mL at rest** — A healthy adult moves approximately 500 mL per breath; multiplied by 12–16 breaths per minute this gives a minute ventilation of 6–8 litres, meeting the body's resting oxygen demand. • During exercise, tidal volume can increase to 2–3 L per breath as the body taps into its inspiratory and expiratory reserve volumes to meet greater oxygen needs. • 💡 Option A (Residual Volume) is wrong because residual volume is the air permanently trapped in the lungs even after maximum exhalation; Option B (Inspiratory Capacity) is wrong because inspiratory capacity is the total air inhaled from resting end-expiration including both tidal and inspiratory reserve volumes; Option D (Vital Capacity) is wrong because vital capacity is the maximum air exhaled after maximum inhalation, encompassing tidal and both reserve volumes.

Correct Answer: C. 200-250 times

• **200–250 times greater affinity** = Carbon monoxide binds to the iron atom in haemoglobin's heme group at the same site as oxygen but with 200–250 times greater affinity, forming a stable compound called carboxyhaemoglobin (COHb). • **Double toxic action** — CO not only prevents oxygen from binding but also distorts the remaining oxygen-binding sites (Bohr effect shift), making it even harder for whatever O2 is bound to be released to tissues, causing rapid cellular hypoxia. • Treatment is high-flow 100% oxygen, which speeds the dissociation of COHb from hours to about 90 minutes; hyperbaric oxygen therapy further accelerates this. • 💡 Option A (2 times) is wrong because a 2-fold higher affinity would be clinically trivial and easily overcome by breathing fresh air; Option B (20–50 times) is wrong because 20–50-fold would be serious but still underestimates the actual danger of CO poisoning; Option D (10 times) is wrong because 10-fold is far below the actual 200–250-fold affinity that makes even small CO concentrations rapidly lethal.

Correct Answer: D. Larynx

• **Larynx** = The larynx marks the anatomical boundary between the upper and lower respiratory tracts; it is the first structure of the lower tract and connects the pharynx above to the trachea below. • **Dual gatekeeper role** — The larynx both generates voice and protects the lower airway; it is the point at which the digestive and respiratory pathways permanently separate. • Clinically, the lower respiratory tract begins at the larynx; infections below this point (e.g., tracheitis, bronchitis, pneumonia) are generally more serious than upper tract infections. • 💡 Option A (Nasal cavity) is wrong because the nasal cavity is the beginning of the upper respiratory tract, the first structure that filters and warms inhaled air; Option B (Trachea) is wrong because the trachea is part of the lower tract but comes after the larynx, making it the second structure; Option C (Pharynx) is wrong because the pharynx is the last structure of the upper respiratory tract, sitting just above the larynx.

Correct Answer: B. At the level of the 5th thoracic vertebra

• **Level of the 5th thoracic vertebra (T5)** = The trachea bifurcates at a ridge called the carina, located at the sternal angle (angle of Louis) anteriorly and at the level of T4–T5 posteriorly, dividing into right and left main bronchi. • **Carina as a landmark** — The carina is a key bronchoscopic landmark; widening or distortion of the carina angle (normally <70°) suggests enlargement of the subcarinal lymph nodes, a sign of lung cancer or lymphoma. • The right main bronchus is wider, shorter, and more vertical than the left, which is why inhaled foreign bodies more commonly lodge in the right lung. • 💡 Option A (Behind the heart) is wrong because the bifurcation is in front of (anterior to) the oesophagus and directly behind the aortic arch, not behind the heart itself; Option C (Just above the diaphragm) is wrong because the bifurcation occurs at mid-chest, well above the diaphragm; Option D (At the level of the neck) is wrong because the larynx and upper trachea are in the neck — the bifurcation is in the thorax.