Free Human Respiratory System MCQs with Answers

1. The correct path taken by inhaled air after it leaves the larynx is

• 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 bronchioles ending in the alveolar sacs where exchange occurs. The sequence runs from wide and few to narrow and numerous, which is the quick way to check any order given in an option. Cartilage supports the trachea and bronchi but disappears in the smallest bronchioles.

2. During swallowing, entry of food into the trachea is prevented by the

• 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 is directed into the oesophagus behind it. The soft palate closes the passage to the nose at the same moment, which is why it is the tempting alternative. The glottis is the opening itself, not the structure that covers it.

3. The rings of cartilage in the wall of the trachea are C shaped rather than complete because

• 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 at the back allows a swallowed bolus to bulge into the space as it passes down the oesophagus behind. Complete rings would give the same support but would obstruct swallowing. The rings do not restrict airflow in any way.

4. During inspiration the diaphragm

• 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 inside the lungs falls below atmospheric and air flows in. The diaphragm is a muscle, so contraction shortens and flattens the dome rather than raising it. Air movement is always the result of a pressure difference created by these volume changes.

5. Quiet expiration at rest is described as a passive process because

• 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 without any muscle actively pulling it down, so no extra energy is spent. Forced expiration during exercise or coughing does use the internal intercostals and the abdominal muscles, which is the active case. Loss of this elasticity in emphysema makes breathing out difficult.

6. The volume of air moved in or out of the lungs during one normal quiet breath is called the

• 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 alveoli. Vital capacity is the much larger volume, around 4,500 cm3, that can be moved between the deepest possible inspiration and the fullest expiration. The two are commonly confused because both are measured on the same spirometer trace.

7. Vital capacity is defined as

• 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 lungs and falls in diseases such as emphysema and fibrosis. The air remaining after the fullest expiration is the residual volume, about 1,200 cm3, which cannot be expelled and keeps the alveoli from collapsing. Total lung capacity is vital capacity plus residual volume.

8. The air that remains in the lungs even after the most forceful expiration is 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 it also lets gas exchange continue between breaths. Because it can never be breathed out, it cannot be measured with a simple spirometer. Its presence is also why lungs float in water, a fact used in forensic medicine to show that a baby breathed after birth.

9. In humans, the exchange of gases between air and blood takes place in the

• 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. The bronchi and trachea are only conducting tubes, with no gas exchange through their walls.

10. The voice box of the human body is the

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

Explanation: The larynx houses the vocal cords, which vibrate as air passes to produce sound. The pharynx is the shared passage above it, and the trachea carries air below, so location identifies each structure.