Problem 23 - Anatomy and Physiology of Animals

Question

The partial pressure of carbon dioxide is \(45 \mathrm{~mm} \mathrm{Hg}\) in the blood and \(40 \mathrm{~mm} \mathrm{Hg}\) in the alveoli. 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.

Step-by-Step Solution

Answer

b. It diffuses into the alveoli.

Step 1: Understanding Diffusion

Diffusion is the movement of gases from an area of higher pressure to an area of lower pressure. In the lungs, gases like oxygen and carbon dioxide move due to differences in their partial pressures.

Step 2: Identify High and Low Pressure Points

Examine the given partial pressures: Carbon dioxide has a partial pressure of 45 mm Hg in the blood and 40 mm Hg in the alveoli.

Step 3: Determine the Direction of Diffusion

Since diffusion moves from high to low pressure, carbon dioxide will move from the blood (45 mm Hg) to the alveoli (40 mm Hg).

Step 4: Evaluate Answer Choices

Option a: CO2 diffuses into the blood is incorrect as diffusion occurs from the blood to the alveoli. Option b: CO2 diffuses into the alveoli is correct based on pressure differences. Option c: States an incorrect premise as there's a clear gradient supporting diffusion. Option d: Decomposition into carbon and oxygen is chemically inaccurate.

Key Concepts

Gas Exchange

Gas exchange is a vital process for maintaining healthy respiratory function and overall survival. It happens in the lungs, where oxygen from inhaled air is exchanged with carbon dioxide from the blood.
Our bodies require oxygen to fuel cells and produce energy, while carbon dioxide, a waste product, needs to be expelled. This process primarily occurs in the alveoli, tiny air sacs in the lungs.
Here's how it works:

• Oxygen enters the alveoli during inhalation, creating an oxygen-rich environment.
• Oxygen diffuses into the blood because the blood has a lower concentration of oxygen.
• At the same time, carbon dioxide diffuses from the blood into the alveoli, due to the higher carbon dioxide concentration in the blood compared to the alveoli.
• During exhalation, carbon dioxide is expelled, completing the cycle of gas exchange.

Understanding gas exchange helps us appreciate how crucial the lungs are in keeping our bodies oxygenated and eliminating waste gases.

Partial Pressure

Partial pressure is a concept used to describe the pressure exerted by a particular gas within a mixture of gases, like the air we breathe.
Each gas in the mixture contributes to the total pressure. For example, in the respiratory system, oxygen and carbon dioxide each have their own partial pressures, which influence how they move during gas exchange.
In the context of our scenario:

• The partial pressure of carbon dioxide is measured in both the blood and the alveoli.
• In the blood, it is 45 mm Hg, while in the alveoli, it is 40 mm Hg.
• These differing pressures create a gradient that drives the movement of gases.

This principle of partial pressures ensures that gases move from areas of higher pressure to areas of lower pressure, facilitating effective gas exchange in the lungs. The gradient in partial pressure is essential for promoting the diffusion of gases where needed.

Diffusion

Diffusion is the natural movement of particles from an area of higher concentration or pressure to an area of lower concentration or pressure.
In the respiratory system, diffusion is the mechanism that allows gases to move between the alveoli and the blood. Here's a closer look at diffusion in action:

• Carbon dioxide in the blood has a higher partial pressure (45 mm Hg) compared to the alveoli (40 mm Hg).
• This pressure difference creates a gradient, encouraging carbon dioxide to diffuse into the alveoli.
• As a result, carbon dioxide leaves the blood, moves into the alveoli, and is eventually expelled when we breathe out.

This simple but powerful process ensures that our bodies efficiently remove carbon dioxide and absorb oxygen. Diffusion is driven by the equilibrium-seeking behavior of molecules, which naturally move to areas of lesser concentration until evenly distributed.