Respiratory System MCQs

The central chemoreceptors in the brain stem increase breathing rate in response to which stimulus?

An increase in CO₂ concentration in the CSF

An increase in CO₂ and H+ concentration in the CSF

A decrease in O₂ concentration in the CSF

A decrease in O₂ concentration in the blood

Carbon dioxide that enters the CSF will react with water to form hydronium ions, and these ions stimulate the central chemoreceptors.

Author: rikazzz Comment

Respiratory System

The respiratory centre of the brain controls the respiratory muscles. Which of the following does NOT happen?

An increase in carbon dioxide blood concentration stimulates peripheral chemoreceptors to signal the respiratory centre.

A decrease in blood pH stimulates peripheral chemoreceptors to signal the respiratory centre.

Hydronium ions cross the blood-brain barrier to directly stimulate the central chemoreceptors of the respiratory centre.

A decrease in oxygen blood concentration stimulates peripheral chemore-ceptors to signal the respiratory centre.

Hydronium ions cannot cross the BBB. Carbon dioxide does and forms hydronium ions which go on to stimulate the central chemoreceptors as the CSF has no buffer to remove them.

Author: rikazzz Comment

Respiratory System

If the spinal cord is severed below C4, what will be the effect on breathing?

Paraplegia will result, but breathing will not be affected.

The intercostal muscles are able to effect ventilation, but the diaphragm will not work.

The diaphragm is able to effect ventilation, but the intercostal muscles will not work.

Independent breathing will not be possible.

The diaphragm is innervated by spinal nerves that leave the spinal cord between C3 and C5, so a break below C4 will leave some the nerves above C4 intact and some diaphragm movement is possible.

Author: rikazzz Comment

Respiratory System

If the partial pressure of oxygen in the air contained in the alveoli of the lungs is 14 kPa, then the partial pressure of oxygen dissolved in the alveolar fluid will be:

Very close to 14 kPa

Significantly greater than 14 kPa

Significantly less than 14 kPa

Unable to be determined without the solubility coefficient of oxygen and the temperature of the alveolar fluid

The amount of a gas that will dissolve in a liquid that is in contact with the gas is determined by the partial pressure of that gas. If pp. of O is 14 kPa, then the concentration of O that is dissolved in the alveolar fluid is also 14 kPa.

Author: rikazzz Comment

Respiratory System

Which of the following lists the components of the respiratory membrane?

Alveolar epithelial cells, capillary endothelial cells and their basement membranes

Fluid and surfactant alveolar epithelial cells, capillary endothelial cells and their basement membranes

Visceral pleura, parietal pleura and serous fluid

Ciliated epithelial cells, mucus cells and secreted mucus

The epithelium of the alveoli and capillary (including the basement membrane) and the fluid covering the alveolar surface (which includes surfactant) together form the respiratory membrane through which gases must pass.

Author: rikazzz Comment

Respiratory System

Which molecule or ion dissolved in blood is able to stimulate the central chemoreceptors of the brain’s respiratory centre?

CO₂

H₃O+

O₂

Ca²⁺

Blood-borne hydronium cannot cross the blood-brain barrier. However, carbon dioxide can and it produces hydronium ions when it is on the brain side of the BBB. As there is no buffer in the CSF, these hydronium ions stimulate the central chemoreceptors of the respiratory centre.

Author: rikazzz Comment

Respiratory System

Which of the following buffer systems of the body is affected by the action of the lungs?

Protein

Monohydrogen phosphate/dihydrogen phosphate

Ammonia/ammonium

Carbonic acid/bicarbonate

Exhaled CO₂ comes from the disassociation of the carbonic acid molecule which in turn forms when a hydronium ion (acid) combines with a bicarbonate ion. Hence, exhaling CO₂ reduces the amount of acid in the blood.

Author: rikazzz Comment

Respiratory System

Mt. Everest “base camp” is located 5300 m above sea level. Here, the atmospheric pressure is 403 mmHg (rather than 760 mmHg at sea level), and the oxygen partial pressure in atmospheric air at this altitude is about 79 mmHg. What is the likely value for dissolved oxygen concentration in arterial blood for someone at base camp?

149 mmHg

104 mmHg

79 mmHg

50 mmHg

This value has been measured in climbers at base camp. If the partial pressure of oxygen gas in the atmosphere is 79 mmHg, the ppO₂ in the alveoli will be less than this, because there is substantial carbon dioxide and water vapour in alveolar air. 149 is the ppO₂ in the atmosphere at sea level, while 104 is ppO₂ in alveolar air at sea level.

Author: rikazzz Comment

Respiratory System

Blood entering the capillaries of the alveoli has dissolved CO₂ at 46 mm Hg and is separated from air in the alveoli, which contains CO₂ at a partial pressure of 40 mm Hg, by the respiratory membrane. What will be the concentration of dissolved CO₂ of the blood capillaries leaving the alveoli?

40 mm Hg

43 mm Hg

46 mm Hg

86 mm Hg

Carbon dioxide will continue to diffuse from blood across the respiratory membrane into the alveoli, while the concentration gradient exists. The gradient will exist until the dissolved CO₂ in the blood in the capillaries falls to 40 mmHg.

Author: rikazzz Comment

Respiratory System

Which structures are called bronchioles?

Respiratory passageways that have cartilage in their walls

The tubes that open from the left and right primary bronchi

The tubes that enter a lobule

The tubes that enter an alveolar sac

Terminal bronchioles supply air to a lobule. Respiratory bronchioles supply air to an alveolar sac. Secondary bronchi diverge from primary bronchi.

Author: rikazzz Comment