alleryStart learning →What are the carbon dioxide partial pressures in pulmonary capillary blood and in alveolar air?
A40 mm Hg in blood and 45 mm Hg in alveoli
B45 mm Hg in blood and 40 mm Hg in alveoli
C45 mm Hg in blood and 104 mm Hg in alveoli
D40 mm Hg in blood and 104 mm Hg in alveoli
Answer & Solution
Correct answer: B. 45 mm Hg in blood and 40 mm Hg in alveoli
1. Blood arriving at the lung has picked up carbon dioxide from the tissues.
2. Its carbon dioxide partial pressure is about 45 mm Hg.
3. Alveolar air sits lower, at about 40 mm Hg.
4. The 5 mm Hg difference sends carbon dioxide from blood into the alveolus, so the first option would reverse the flow.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.4 Gas Exchange_
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