Under normal, resting conditions, the partial pressures of oxygen and carbon dioxide in arterial blood remain:

• A. relatively constant due to homeostatic regulation
• B. equal to each other at all times
• C. zero because gases are rapidly exchanged
• D. highly variable depending on metabolic activity

Answer: (A)

Verified step by step guidance

1. Understand the concept of partial pressure: Partial pressure refers to the pressure exerted by a single type of gas in a mixture of gases. In the context of blood, it represents the concentration of oxygen (O₂) and carbon dioxide (CO₂) dissolved in the blood.
2. Learn about homeostasis: Homeostasis is the body's ability to maintain stable internal conditions, including the regulation of oxygen and carbon dioxide levels in arterial blood, despite changes in external or internal conditions.
3. Recognize the role of respiratory and circulatory systems: The respiratory system ensures gas exchange in the lungs, while the circulatory system transports oxygen and carbon dioxide to and from tissues. These systems work together to maintain relatively constant partial pressures of O₂ and CO₂ in arterial blood under normal conditions.
4. Evaluate the options: Analyze each answer choice based on biological principles. For example, 'relatively constant due to homeostatic regulation' aligns with the body's ability to maintain stable gas levels, while 'equal to each other at all times' is incorrect because O₂ and CO₂ have different partial pressures. Similarly, 'zero because gases are rapidly exchanged' and 'highly variable depending on metabolic activity' contradict the concept of homeostasis.
5. Conclude based on reasoning: The correct answer is 'relatively constant due to homeostatic regulation,' as the body actively regulates the partial pressures of oxygen and carbon dioxide to ensure proper cellular function and metabolic balance.