Free Human Respiratory System MCQs with Answers

• A. trachea, alveoli, bronchi, bronchioles
• B. bronchi, trachea, bronchioles, alveoli
• C. trachea, bronchi, bronchioles, alveoli
• D. bronchioles, bronchi, trachea, alveoli

Explanation: Air passes down the single trachea, which divides into two bronchi, one to each lung, and these branch repeatedly into ever finer…

• A. epiglottis
• B. uvula
• C. soft palate
• D. glottis

Explanation: The epiglottis is a flap of cartilage that folds back over the opening of the larynx as the larynx rises during swallowing, so the bolus…

• A. complete rings would restrict the flow of air
• B. cartilage is too expensive for the body to make
• C. the gap allows nerves to reach the lung
• D. the incomplete side lies against the oesophagus and lets it expand during swallowing

Explanation: The cartilage keeps the airway permanently open so it cannot collapse when pressure falls during inspiration, while the soft muscular gap…

• A. contracts and flattens, increasing the volume of the thorax
• B. relaxes and domes upwards, increasing the volume of the thorax
• C. contracts and domes upwards, decreasing the volume of the thorax
• D. does not move at all

Explanation: A flattening diaphragm and the external intercostals swinging the ribs up and out together enlarge the thoracic cavity, so the pressure…

• A. no air actually leaves the lungs
• B. the internal intercostal muscles contract forcefully
• C. it results from the elastic recoil of the lungs and relaxation of the inspiratory muscles
• D. the diaphragm contracts to push air out

Explanation: When the diaphragm and external intercostals simply relax, the stretched elastic tissue of the lungs recoils and the thoracic volume falls…

• A. vital capacity
• B. tidal volume
• C. residual volume
• D. total lung capacity

Explanation: The tidal volume of an adult at rest is about 500 cm3, of which roughly 150 cm3 stays in the airways as dead space and never reaches the…

• A. the air left in the lungs after the deepest possible expiration
• B. the volume of one quiet breath
• C. the volume of air in the dead space
• D. the maximum volume of air that can be expelled after the deepest possible inspiration

Explanation: Vital capacity is the sum of the tidal volume and the inspiratory and expiratory reserve volumes, so it measures the usable range of the…

• A. tidal volume
• B. inspiratory reserve volume
• C. residual volume
• D. vital capacity

Explanation: About 1,200 cm3 cannot be expelled, and this residual volume keeps the alveoli partly inflated so they do not collapse and stick shut, and…

• A. alveoli
• B. bronchi
• C. trachea
• D. larynx

Explanation: The millions of thin walled alveoli provide the enormous surface where oxygen enters the blood and carbon dioxide leaves.

• A. pharynx
• B. larynx
• C. trachea
• D. nasal cavity

Explanation: The larynx houses the vocal cords, which vibrate as air passes to produce sound.

• A. trachea
• B. larynx
• C. pharynx
• D. bronchus

Explanation: The pharynx receives air from the nose and food from the mouth and directs them onwards, which is why swallowing must temporarily close…

• A. alveoli
• B. alveolar ducts
• C. pleural sacs
• D. two bronchi

Explanation: Each primary bronchus enters a lung and branches into ever finer bronchioles ending in alveoli.

• A. pleura
• B. pericardium
• C. peritoneum
• D. meninges

Explanation: The pleura secretes fluid that lets the lungs slide smoothly against the chest wall during breathing.

• A. 6 per minute
• B. 16 per minute
• C. 40 per minute
• D. 75 per minute

Explanation: Quiet breathing runs at roughly 12 to 20 cycles per minute, around 16. The figure 75 per minute belongs to the heart rate, and examiners…

• A. the abdominal muscles only
• B. the internal intercostal muscles only
• C. the external intercostal muscles
• D. the smooth muscles of the alveoli

Explanation: The external intercostals lift the rib cage up and out, enlarging the thorax with the diaphragm's downward pull.

• A. glomeruli
• B. villi
• C. cisternae
• D. alveoli

Explanation: Alveoli hang in grape like clusters at the end of the airways, each wrapped in capillaries.

• A. nasal cavity
• B. trachea only
• C. bronchi
• D. alveoli

Explanation: Hairs and mucus trap particles while blood vessels warm the air and secretions humidify it before it reaches delicate lung tissue.

• A. fluid filling the alveoli
• B. constriction of the bronchi and bronchioles with excess mucus
• C. destruction of the cartilage rings of the trachea
• D. paralysis of the diaphragm

Explanation: The airway smooth muscle contracts and the lining swells with mucus, narrowing the tubes so air whistles through.

• A. the blood actively pumps it in
• B. the alveolar walls are impermeable to nitrogen
• C. the partial pressure of oxygen is higher in the alveoli than in the blood
• D. plasma proteins pull it across

Explanation: Gases always diffuse down their partial pressure gradients, and incoming alveolar air carries more oxygen than the arriving deoxygenated…

• A. dissolved in the plasma
• B. as bicarbonate ions
• C. as carboxyhaemoglobin
• D. bound to haemoglobin inside red blood cells

Explanation: About 97 per cent of oxygen rides on haemoglobin as oxyhaemoglobin, while only a small fraction dissolves in plasma.