Respiratory System — Set 3

Correct Answer: A. Nasal Cavity

• **Nasal Cavity** = The nasal cavity is lined with pseudostratified ciliated epithelium covered in mucus; coarse nasal hairs (vibrissae) trap large particles and the mucus layer captures finer dust, bacteria, and allergens. • **Warming via turbinates** — Three bony shelves called turbinates (conchae) create turbulent airflow that maximises contact between inhaled air and the richly vascularised mucous membrane, warming air to near body temperature (37°C) before it reaches the lungs. • Humidification also occurs here; dry inhaled air is brought to nearly 100% relative humidity by the time it reaches the alveoli, protecting delicate lung surfaces. • 💡 Option B (Alveoli) is wrong because alveoli are exclusively gas-exchange surfaces — by the time air reaches them it must already be clean, warm, and moist; Option C (Trachea) is wrong because the trachea does continue mucus clearance via its ciliated lining but is not the primary site of warming and filtering; Option D (Lungs) is wrong because the lungs as a whole are gas-exchange organs and rely on the nose and upper airways to pre-condition incoming air.

Correct Answer: B. Residual Volume

• **Residual Volume** = Residual volume (RV) is the air that cannot be expelled from the lungs by any voluntary effort; it exists because the chest wall's outward recoil prevents the lungs from fully collapsing. • **Prevents alveolar collapse** — The ~1.2 L of residual air keeps alveoli partially open, maintaining a surface for continuous gas exchange even at the end of maximal exhalation and preventing atelectasis (lung collapse). • Residual volume cannot be measured by simple spirometry; it requires gas dilution techniques or body plethysmography, and it increases abnormally in emphysema as air becomes trapped. • 💡 Option A (Tidal Volume) is wrong because tidal volume is the volume moved during a quiet normal breath, not what remains after maximal exhalation; Option C (Expiratory Reserve Volume) is wrong because ERV is the extra air that can be forcefully exhaled beyond normal tidal exhalation — it is measurable and can be expelled, unlike residual volume; Option D (Vital Capacity) is wrong because vital capacity is the maximum amount of air that can be moved and specifically excludes residual volume.

Correct Answer: D. Emphysema

• **Emphysema** = Emphysema is a chronic obstructive disorder in which cigarette smoke activates lung macrophages and neutrophils that release proteases (especially elastase), destroying the elastic fibres and walls of alveoli, merging them into large, inelastic air sacs. • **Loss of elastic recoil** — Destroyed elastic fibres mean the lungs can no longer passively recoil during exhalation, trapping air and producing the characteristic barrel chest, prolonged expiration, and pursed-lip breathing seen in patients. • The total surface area for gas exchange plummets as alveoli merge, causing chronic hypoxaemia even at rest in advanced disease. • 💡 Option A (Asthma) is wrong because asthma is characterised by reversible bronchoconstriction triggered by allergens or irritants, not by permanent alveolar wall destruction; Option B (Tuberculosis) is wrong because TB is caused by the bacterium Mycobacterium tuberculosis forming granulomas, primarily in the lung apices; Option C (Pneumonia) is wrong because pneumonia is an acute infection causing alveolar consolidation with fluid and inflammatory cells, not chronic structural destruction.

Correct Answer: B. External respiration

• **External respiration** = External respiration encompasses both ventilation (the physical movement of air into and out of the lungs) and pulmonary gas exchange (the diffusion of O2 from alveolar air into pulmonary capillary blood and CO2 in the opposite direction). • **First step in the oxygen cascade** — External respiration loads oxygen onto haemoglobin in the pulmonary capillaries and unloads CO2 into alveolar air, completing the first leg of the journey from atmosphere to cells. • The efficiency of external respiration depends on matching of alveolar ventilation to capillary perfusion (the V/Q ratio); mismatches cause hypoxaemia. • 💡 Option A (Cellular respiration) is wrong because cellular respiration is the biochemical process inside cells that oxidises glucose to produce ATP, CO2, and water; Option C (Anaerobic respiration) is wrong because anaerobic respiration is glucose breakdown without oxygen, producing lactic acid — it is a metabolic process, not gas exchange; Option D (Internal respiration) is wrong because internal respiration is the exchange of gases between systemic capillaries and body tissues, not at the lungs.

Correct Answer: C. Spirometer

• **Spirometer** = A spirometer measures the volumes and flow rates of air inhaled and exhaled, generating a graphical record called a spirogram that displays tidal volume, inspiratory reserve, expiratory reserve, and vital capacity. • **Diagnostic power** — The key spirometric indices FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) and their ratio distinguish obstructive diseases like asthma and COPD from restrictive diseases like pulmonary fibrosis. • Spirometry is the gold-standard lung function test; it is simple, non-invasive, and used worldwide to monitor disease progression and treatment response. • 💡 Option A (Sphygmomanometer) is wrong because a sphygmomanometer measures blood pressure using an inflatable cuff and pressure gauge; Option B (Hygrometer) is wrong because a hygrometer measures atmospheric humidity, not lung volumes; Option D (Stethoscope) is wrong because a stethoscope is an acoustic device used to listen to breath sounds, heart sounds, and bowel sounds — it does not measure volume.

Correct Answer: A. Pharynx

• **Pharynx** = The pharynx is a 12–14 cm muscular funnel that receives air from the nasal cavity and mouth and food from the mouth, serving as the shared crossroads before the two pathways diverge at the larynx. • **Three anatomical regions** — The nasopharynx (posterior to the nose) carries only air; the oropharynx and laryngopharynx (posterior to the mouth and larynx) carry both air and food, which is why careful swallowing coordination is essential. • The pharynx also houses the palatine and pharyngeal tonsils (adenoids), important components of the immune system's first line of defence against inhaled and ingested pathogens. • 💡 Option B (Larynx) is wrong because the larynx is exclusively an air passage — the epiglottis seals it during swallowing to ensure food does not enter; Option C (Esophagus) is wrong because the oesophagus carries only food and liquids to the stomach, with no air passage function; Option D (Trachea) is wrong because the trachea is a dedicated air conduit leading to the bronchi — it does not carry food.

Correct Answer: C. Three

• **Three lobes** = The right lung is divided by the horizontal and oblique fissures into three lobes: the upper (superior), middle, and lower (inferior) lobes. • **Right lung is larger** — The right lung is shorter (the liver pushes the right diaphragm up) but wider and heavier (~620 g vs ~560 g for the left), and receives slightly more blood flow, making right-sided lung pathology more common. • The left lung has only two lobes (upper and lower) because the heart occupies a cardiac notch in the left thoracic cavity, taking up space that the middle lobe would otherwise occupy. • 💡 Option A (Four) is wrong because no human lung has four lobes; accessory fissures may occasionally create extra segments but this is an anatomical variant; Option B (One) is wrong because even the smaller left lung has two distinct lobes; Option D (Two) is wrong because two lobes describe the left lung, not the right — the right lung distinctively has three lobes separated by two fissures.

Correct Answer: B. Reduce friction during breathing

• **Friction reduction** = Pleural fluid fills the microscopic space between the visceral and parietal pleura, acting as a lubricant so the two membrane surfaces glide smoothly over each other during the constant expansion and recoil of breathing. • **Surface tension creates lung adherence** — The thin layer of fluid also creates surface tension between the two pleural layers, causing the lungs to adhere to the chest wall and follow its movements during inspiration and expiration. • Normal pleural fluid volume is only 5–15 mL; excessive accumulation (pleural effusion) can compress the lung and reduce breathing capacity, requiring drainage (thoracentesis). • 💡 Option A (Trap dust particles) is wrong because dust trapping is performed by nasal hairs, mucus, and cilia in the upper airways — pleural fluid is enclosed in the chest and never contacts inhaled air; Option C (Transport of oxygen) is wrong because oxygen transport is performed by haemoglobin in red blood cells, not by pleural fluid; Option D (Neutralize acids) is wrong because acid-base balance is maintained by bicarbonate buffers in the blood and by the kidneys, not by pleural fluid.

Correct Answer: C. Oxygen

• **Oxygen** = The Haldane effect states that deoxygenated haemoglobin (deoxy-Hb) binds CO2 and hydrogen ions more readily than oxygenated haemoglobin, so tissues where O2 has been unloaded are better able to load CO2 for transport back to the lungs. • **Complementary to the Bohr effect** — The Bohr effect (CO2 reduces Hb's affinity for O2) and the Haldane effect (O2 reduces Hb's affinity for CO2) work as a coordinated pair: in tissues, releasing O2 enhances CO2 pickup; in the lungs, picking up O2 drives CO2 release. • Quantitatively, the Haldane effect accounts for about 60% of the total CO2 transported in venous blood through carbaminohaemoglobin formation. • 💡 Option A (Nitrogen) is wrong because nitrogen is physiologically inert under normal atmospheric conditions and has no interaction with haemoglobin's gas-binding chemistry; Option B (Hydrogen) is wrong because hydrogen gas is not present in the respiratory system — hydrogen ions (H⁺) are involved in pH, but the Haldane effect is specifically about molecular oxygen and CO2; Option D (Methane) is wrong because methane is produced in trace amounts by gut bacteria and is exhaled, but plays no role whatsoever in haemoglobin chemistry or CO2 transport.

Correct Answer: D. Asthma

• **Asthma** = Asthma is a chronic inflammatory disease of the airways in which allergens or irritants trigger an IgE-mediated immune response, causing bronchospasm, mucosal swelling, and excess mucus secretion that collectively narrow the bronchial lumen. • **Reversible airflow obstruction** — Unlike emphysema, asthmatic episodes are largely reversible; bronchodilators (e.g., salbutamol) relax bronchial smooth muscle within minutes, restoring normal airflow — which is the hallmark distinguishing asthma from COPD. • Common triggers include pollen, dust mites, pet dander, mould spores, cold air, exercise, and certain medications such as aspirin or beta-blockers. • 💡 Option A (Emphysema) is wrong because emphysema results from permanent destruction of alveolar walls by smoking-induced proteases, not from an allergic IgE-mediated mechanism; Option B (Silicosis) is wrong because silicosis is caused by occupational inhalation of silica dust leading to lung fibrosis, not allergy; Option C (Pneumonia) is wrong because pneumonia is an acute infection of lung tissue caused by bacteria, viruses, or fungi — it is not a chronic allergic condition.