Question

Which of these statements about the partial pressure of carbon dioxide is true? a. It is higher in the alveoli than in the pulmonary arteries. b. It is higher in the systemic arteries than in the tissues. c. It is higher in the systemic veins than in the systemic arteries. d. It is higher in the pulmonary veins than in the pulmonary arteries.

Short answer

The correct statement about the partial pressure of carbon dioxide is: "It is higher in the systemic veins than in the systemic arteries."

Step-by-step solution

Understand partial pressure

Partial pressure refers to the pressure exerted by a specific gas in a mixture of gases. In this exercise, we are concerned with the partial pressure of carbon dioxide (CO2) in different parts of the respiratory and circulatory systems.

Examine each statement

We will now analyze each statement and verify its correctness based on our understanding of partial pressure and the respiratory and circulatory systems. a. "It is higher in the alveoli than in the pulmonary arteries." Alveoli are the small air sacs in the lungs where gas exchange occurs. Pulmonary arteries carry oxygen-poor, CO2-rich blood from the heart to the lungs to release CO2 and pick up oxygen. Since the primary function of the alveoli is to remove CO2 from the blood, the partial pressure of CO2 must be higher in the pulmonary arteries than in the alveoli. Therefore, this statement is false. b. "It is higher in the systemic arteries than in the tissues." Systemic arteries carry oxygen-rich, CO2-poor blood from the heart to the rest of the body. As the blood reaches the tissues, it delivers oxygen and picks up CO2 produced by cellular respiration. Thus, the partial pressure of CO2 is lower in the systemic arteries than in the tissues. This statement is also false. c. "It is higher in the systemic veins than in the systemic arteries." Systemic veins are responsible for carrying oxygen-poor, CO2-rich blood from the tissues back to the heart. As mentioned earlier, the partial pressure of CO2 is lower in the systemic arteries than in the tissues. Therefore, this statement is true. d. "It is higher in the pulmonary veins than in the pulmonary arteries." Pulmonary veins carry oxygen-rich, CO2-poor blood from the lungs back to the heart. Since pulmonary arteries have a higher partial pressure of CO2 than the alveoli, it is expected that the partial pressure of CO2 is lower in the pulmonary veins than in the pulmonary arteries. This statement is false.

Conclusion

The correct statement about the partial pressure of carbon dioxide is: "It is higher in the systemic veins than in the systemic arteries."

Key concepts

Respiratory System

The respiratory system is responsible for providing our bodies with the oxygen needed to sustain life while removing carbon dioxide (CO2), a waste product of metabolism. This system includes structures such as the nose, trachea, bronchi, and lungs. Inside the lungs, the primary components for gas exchange are the alveoli, tiny sac-like structures surrounded by capillaries.

Alveoli play a crucial role by increasing the surface area for gas exchange, ensuring efficient oxygen uptake and CO2 release. When air is inhaled, oxygen moves into the bloodstream through the thin walls of the alveoli, while CO2 is transferred from the blood to the alveoli to be exhaled.

The concept of partial pressure helps us understand how gases like CO2 and oxygen are exchanged. Partial pressure is essentially the pressure exerted by a single gas in a mixture. It's vital for these pressures to be balanced correctly to maintain proper breathing function and overall homeostasis.

Circulatory System

The circulatory system, also known as the cardiovascular system, works closely with the respiratory system to transport gases, nutrients, and waste products throughout the body. It consists of the heart, blood, and blood vessels, including arteries, veins, and capillaries.

Blood in this system is a mixture of cells and plasma that travels in a loop: from the heart to the lungs and back, and then around the body. In terms of carbon dioxide, this gas is carried mainly in the form of bicarbonate ions or dissolved in plasma.

In the exercise problem, understanding the various pressures of CO2 in different parts of the circulatory system is key. For instance:

• Systemic arteries carry lower-CO2 blood from the heart to the tissues.
• Systemic veins return higher-CO2 content blood from the tissues back to the heart.
• Pulmonary arteries carry CO2-rich blood to the lungs for gas exchange.
• Pulmonary veins bring back oxygen-rich blood, now low in CO2, to the heart.

All of these pathways work in harmony to ensure tissues receive oxygen and are rid of CO2 effectively.

Gas Exchange

Gas exchange is the critical process where oxygen is taken from the environment into the bloodstream, and carbon dioxide is expelled from the blood into the atmosphere. This exchange occurs primarily in the lungs' alveoli, leveraging the differences in partial pressures of these gases.

How does this work? Imagine gases moving from areas of high concentration to low concentration — this is diffusion. In the alveoli:

• Oxygen diffuses into the blood because its partial pressure is higher in the alveoli compared to the blood.
• Carbon dioxide does the opposite, moving from blood (where its partial pressure is higher) to the alveoli to be exhaled.

This efficient swap is essential for maintaining the body's acid-base balance and ensuring cells receive energy through respiration.

In both the systemic and pulmonary circuits, understanding the flow and partial pressures is indispensable for interpreting physiological conditions and any potential misconceptions about where CO2 concentrations lie at different stages in the cycle.