Question

The partial pressure of carbon dioxide is \(45 \mathrm{~mm} \mathrm{Hg}\) in the blood and \(40 \mathrm{~mm} \mathrm{Hg}\) in the a lveoli. What happens to the carbon dioxide? a. It diffuses into the blood. b. It diffuses into the alveoli. c. The gradient is too small for carbon dioxide to diffuse. d. It decomposes into carbon and oxygen.

Short answer

Answer: (b) It diffuses into the alveoli.

Step-by-step solution

Define the concept of gas diffusion

Gas diffusion is the spontaneous movement of gas molecules from a region of higher partial pressure to a region of lower partial pressure. In our case, we need to determine in which direction the carbon dioxide molecules will move.

Compare the given partial pressures

We are given the partial pressure of carbon dioxide in the blood as \(45 \mathrm{~mm} \mathrm{Hg}\) and in the alveoli as \(40 \mathrm{~mm} \mathrm{Hg}\). In looking at these pressures, we can see that the partial pressure of carbon dioxide is higher in the blood than in the alveoli.

Apply the concept of gas diffusion to the given partial pressures

Since the partial pressure of carbon dioxide is higher in the blood (\(45 \mathrm{~mm} \mathrm{Hg}\)) than in the alveoli (\(40 \mathrm{~mm} \mathrm{Hg}\)), according to the concept of gas diffusion, the carbon dioxide molecules will spontaneously move from the blood to the alveoli.

Choose the correct answer

Based on our analysis, the correct answer is: (b) It diffuses into the alveoli.

Key concepts

Partial Pressure

Understanding the concept of partial pressure is critical when studying respiratory physiology and gas exchange. It's a measurement of the pressure exerted by a single type of gas in a mixture of gases. Simply put, the partial pressure of a gas reflects how much of that gas is present in a mixture and its tendency to diffuse from a higher to a lower concentration area.

For instance, in the context of the textbook exercise, the partial pressure of carbon dioxide (CO2) in the blood was given as 45 mm Hg, and in the alveoli as 40 mm Hg. This difference in partial pressures drives the diffusion process, where CO2 moves from the bloodstream (where its partial pressure is higher) to the alveoli (where its partial pressure is lower). This property is fundamental to understanding how gases move across respiratory surfaces such as the alveoli in the lungs.

Alveolar Gas Exchange

Alveolar gas exchange is the heart of respiration, where the necessary exchange of gases between our blood and the outside environment occurs. This exchange happens in the alveoli, tiny sac-like structures in the lungs where blood rich in carbon dioxide is pumped in from the body, and oxygen from inhaled air is waiting to be taken up.

During this exchange, gases move according to their partial pressures; oxygen enters the blood where its partial pressure is lower, and carbon dioxide exits the blood where its pressure is higher. Returning to the exercise's scenario, the carbon dioxide possesses a higher partial pressure in the blood than in the alveoli, and so it diffuses into the alveoli. Effective gas exchange is crucial for maintaining the oxygen and carbon dioxide levels essential for cellular respiration and the proper functioning of the body.

Respiratory Physiology

Respiratory physiology encompasses the study of how gases are taken in, transported, and expelled from the human body. It involves several processes that include ventilation (breathing), external respiration (the exchange of gases between the air in the alveoli and the blood), transport of gases by the blood, internal respiration (the exchange of gases between the blood and the cells), and cellular respiration (the process cells use to make energy).

In relation to our exercise, understanding how carbon dioxide is removed from the blood through the alveoli is a small yet critical piece of the larger picture of respiratory physiology. This removal is driven by the diffusion gradient dictated by partial pressures, illustrating why knowledge in this subject is essential for grasping how our bodies sustain life through breathing.