Which of the following statements about partial pressures of gases in the tissues is true?

• A. The partial pressure of carbon dioxide is higher in tissues than in the alveoli.
• B. The partial pressure of oxygen is higher in tissues than in the alveoli.
• C. The partial pressure of water vapor is lower in tissues than in the alveoli.
• D. The partial pressure of nitrogen is significantly higher in tissues than in the atmosphere.

Answer: (A)

Verified step by step guidance

1. Understand the concept of partial pressure: Partial pressure is the pressure exerted by a single type of gas in a mixture of gases. It is proportional to its concentration in the mixture.
2. Consider the physiological context: In the human body, gases like oxygen (O2) and carbon dioxide (CO2) are exchanged between the blood and tissues, and between the blood and alveoli in the lungs.
3. Analyze the partial pressure of carbon dioxide: In tissues, cells produce CO2 as a waste product of metabolism, leading to a higher partial pressure of CO2 in tissues compared to the alveoli, where CO2 is expelled.
4. Analyze the partial pressure of oxygen: Oxygen is delivered to tissues from the blood, resulting in a lower partial pressure of O2 in tissues compared to the alveoli, where O2 is inhaled.
5. Consider the partial pressures of water vapor and nitrogen: Water vapor is generally higher in the alveoli due to humidification of inhaled air. Nitrogen, being inert, has a relatively constant partial pressure and is not significantly higher in tissues than in the atmosphere.