Relate vessels to function
Connect the structure of arteries, veins, and capillaries to the job each one does in circulation.
- Blood flows away from and back to the heart: Vessels are defined by direction relative to the heart, so this direction idea comes first.
- Structure fits function: Each vessel's wall thickness and size match its job: the core reasoning move in this skill.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Each vessel's structure fits its job: arteries have thick walls for high pressure, veins have valves to stop backflow, and capillaries have walls one cell thick for exchange.
The table shows a structural feature of each vessel type. Which vessel's structure best fits the job of exchanging oxygen and nutrients with body cells?
Reviewed| Vessel | Structural feature |
|---|---|
| Artery | Thick, muscular, elastic wall |
| Vein | Thinner wall with one-way valves |
| Capillary | Wall only one cell thick |
- A.Artery, because of its thick muscular wall
- B.Capillary, because of its wall one cell thick
- C.Vein, because of its one-way valves
- D.All three equally, because they all carry blood
Show the worked solution ▾
Answer: B. Capillary, because of its wall one cell thick
- Step 1: Recall what exchange needs: Exchanging oxygen and nutrients means substances must pass through the vessel wall, so a very thin wall is needed.
- Step 2: Read the table: The capillary has a wall only one cell thick, the thinnest of the three, so it is built for exchange.
Why it's right: A capillary's wall is only one cell thick, which lets oxygen and nutrients diffuse between the blood and body cells: the structure that fits the exchange job.
- A: An artery's thick wall handles high pressure but is too thick for exchange.
- C: A vein's valves stop backflow; they do not enable exchange, and its wall is thicker than a capillary's.
- D: The three vessels have different structures and do different jobs; they are not equal at exchange.
Aligned to HBS 3.1: structure fits function · reading level ~grade 9
- A doctor pressing a fingertip to check capillary refill is testing the tiny exchange vessels, where blood is closest to the skin's cells.
Fill these in as you work through the lesson.
- Artery (carries blood away from the heart):
- Vein (carries blood back toward the heart):
- Capillary (tiny vessel where exchange happens):
- Valve (in a vein) (one-way flap that stops backflow):
- Diffusion / exchange (oxygen and nutrients passing through thin walls):
Arteries carry blood from the heart and have walls for high pressure. Veins carry blood the heart and have to stop backflow. Capillaries have walls so substances can be exchanged.
- Why do arteries need thicker walls than veins?
- What feature helps veins move blood back toward the heart against gravity?
- Why must capillary walls be only one cell thick?
Given a vessel described as 'thin-walled, one cell thick, found between tissue cells,' name the vessel type and explain how its structure fits its function.