Question

which of the following are narrow blood vessels that restrict blood flow and have thin walls that allow gas exchange?

• alveoli
• veins
• arteries
• capillaries

Explanation:

🆕 New Concept Discovered: Structure and function of blood vessels
How vessel wall thickness relates to transport and exchange

Step 1: Analyze the requirements

The question asks for a structure that meets three specific criteria:

1. It is a blood vessel.
2. It is narrow and restricts blood flow (slowing it down).
3. It has thin walls that allow for gas exchange.

Step 2: Evaluate the options

• Alveoli: These are tiny air sacs in the lungs where gas exchange occurs, but they are part of the respiratory system, not blood vessels.
• Veins: These are larger blood vessels that carry blood back to the heart. They have thinner walls than arteries but are too thick to allow direct gas exchange.
• Arteries: These are thick-walled, muscular blood vessels that carry blood away from the heart under high pressure. Their thick walls do not allow for gas exchange.
• Capillaries: These are the smallest and narrowest blood vessels. Their walls are only one cell thick (extremely thin), which slows down blood flow and allows oxygen, carbon dioxide, and nutrients to easily diffuse between the blood and surrounding tissues.

Answer:

Capillaries