Respiratory System MCQs

The respiratory system helps the body regulate the pH of blood. How is this done?

The alveolar epithelial cells secrete the monohydrogen/dihydrogen phos-phate buffer which is able to maintain blood pH.

The CO₂ exhaled causes carbonic acid in the blood to disassociate into water and CO₂ which in turn allows bicarbonate to react with hydronium ions to form more carbonic acid.

The alveolar epithelial cells produce angiotensin-converting enzyme which promotes the formation of the bicarbonate buffer in the blood.

The inhaled O₂ causes dihydrogen phosphate to convert to monohydrogen phosphate which is able to destroy acid.

H₃O⁺ + HCO₃− ↔ H₂CO₃ + H₂O ↔ 2H₂O + CO₂ so when carbon dioxide is breathed out, the reaction “progresses to the right”. Hydronium ions react to form carbonic acid which in turn dissociates into water and carbon dioxide, thus removing acid. The other choices are nonsense.

Author: rikazzz Comment

Respiratory System

According to Boyle’s law, the pressure in a fixed amount of gas will increase as its volume decreases. Which one of the statements that follow is consistent with Boyle’s law?

When the diaphragm contracts, pressure in the lungs increases.

When the chest recoils during exhalation, the air in the lungs is at a negative pressure.

When the chest recoils during exhalation, the air in the lungs increases in volume.

When the diaphragm contracts, pressure in the lungs decreases.

The diaphragm moves inferiorly as it contracts. This expands the volume of the lungs.

Author: rikazzz Comment

Respiratory System

Where does the actual gas exchange between inspired air and the blood in the capillaries occur? In the:

Bronchi

Bronchioles

Alveolar ducts and alveoli

Respiratory bronchioles

Gas exchange occurs across the respiratory membrane of the alveoli and ducts.

Author: rikazzz Comment

Respiratory System

Given that deoxygenated blood entering the alveolar capillaries has an oxygen partial pressure of 42 mmHg and a carbon dioxide partial pressure of 47 mmHg, while the partial pressures of O₂ and CO₂ in the alveolar air are 103 mmHg and 40 mmHg, respectively, which of the following gas movements will occur?

Both CO₂ and O₂ move from alveolar air to the capillaries.

CO₂ moves from alveolar air to capillaries and O₂ moves from capillaries to the alveolar air.

Both CO₂ and O₂ move from capillaries to alveolar air.

CO₂ moves from capillaries to alveolar air and O₂ moves from alveolar air to the capillaries.

Dissolved substances will diffuse from where they are in high concentration to where they are at lower concentration. So O₂ moves from alveolar air (where it is at 103 mmHg) to the capillaries (at 42 mmHg), while CO₂ moves from capillaries (47 mmHg) to alveolar air (40 mmHg).

Author: rikazzz Comment

Respiratory System

What function is served by the goblet/mucus cells of the bronchial “tree”?

They trap small inhaled particles.

They secrete mucus onto the surface of the airways.

They increase the surface area available for gas exchange.

They move mucus up the bronchial tree.

Goblet cells produce mucus to trap any inhaled particles before they reach the alveoli.

Author: rikazzz Comment

Respiratory System

At a height of 3000 m above sea level, atmospheric pressure is 30 kPa less than at sea level. A consequence of this lower pressure is that less oxygen will dissolve in the alveolar fluid. The reason for this is that:

The solubility coefficient of oxygen is lower.

The partial pressure of oxygen in the atmosphere is lower.

Water vapour evaporating from the lung will exert a greater partial pressure.

There will be more carbon dioxide leaving the blood and entering the alveoli.

At 3000 m, atmospheric pressure is 70 kPa, and the oxygen partial pressure is 20% of this (about 14 kPa). 14 kPa is less than 20 kPa (oxygen’s partial pressure at sea level), so less oxygen will dissolve in the alveolar fluid at 3000 m than at sea level.

Author: rikazzz Comment

Respiratory System

Henry’s law relates the amount of gas that will dissolve in a liquid to the partial pressure of the gas in contact with the liquid. In which situation would the greatest amount of oxygen dissolve in the liquid lining the alveoli?

Breathing in an atmosphere at normal pressure but enriched to 30% oxygen

Resting in a mountain range at a height of 3000 m above sea level

Seated inside a hyperbaric chamber at a pressure of three atmospheres

Scuba diving at a depth of 10 m underwater

The pp of oxygen in the situations described by choices B, A, D and C are 0.7X, 1.5X, 2X and 3X, respectively, the pp of oxygen at one atmosphere pressure. Hence, choice C would result in the greatest amount of oxygen dissolving in liquid.

Author: rikazzz Comment

Respiratory System

A bronchiole differs from tertiary (and smaller) bronchi in that it:

Has cartilage in its wall (and bronchi do not)

Does not have cartilage in its wall (and bronchi do)

Has smooth muscle in its wall (and bronchi do not)

Does not have smooth muscle in its wall (and bronchi do)

While bronchi are held rigidly open by their cartilage, bronchioles do not have cartilage in their wall.

Author: rikazzz Comment

Respiratory System

With regard to the respiratory centre, which of the following is TRUE?

Blood oxygen concentration affects the respiratory centre.

Anaesthetics don’t affect respiration.

Raised intracranial pressure increases ventilation.

Narcotic drugs may depress ventilation.

Anaesthesia or narcotics (e.g. morphine) can depress respiratory centres (which decreases ventilation). Raised intracranial pressure can also depress respiration. It is CO₂ concentration rather than O₂ concentration that affects the respiratory centre of the brain.

Author: rikazzz Comment

Respiratory System

What ensures that the lungs expand as the chest wall expands?

Secreted surfactant

Negative pressure between the pleura

Serous liquid secreted by the pleura

The elastic recoil of the alveolar tissue

Negative pressure (suction) causes the visceral pleura to remain in contact with the parietal pleura, so that when the chest wall and parietal pleura move, the parietal pleura takes the visceral pleura and lungs with it.

Author: rikazzz Comment