Every feature of a blood vessel matches a job. Arteries handle high pressure, veins handle slow return, and capillaries handle exchange.
This lesson belongs to transport in humans and animals. You need the route from tracing circulation through the heart to know which vessel carries what.
What is the logic behind the differences?
Ask two questions: how much pressure does the blood face, and does this vessel need to exchange materials? The answers give you every feature.
High pressure means a thick, elastic wall and a narrow lumen. Low pressure means a wider lumen and valves. Exchange means a wall one cell thick.
How do the three vessels compare?
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Direction | Away from the heart | Towards the heart | Between arteries and veins |
| Wall | Thick, muscular, elastic | Thin | One cell thick |
| Lumen | Narrow | Wide | Very narrow |
| Valves | Absent | Present | Absent |
| Pressure | High | Low | Falling |
| Job | Carry blood quickly under pressure | Return blood to the heart | Exchange materials with cells |
Worked example: name the vessel from a description
Question: vessel R has a thin wall, a wide lumen and valves along its length. It carries blood from the leg to the heart. Name R and justify your answer.
- Valves are found in veins, because the blood is at low pressure.
- The direction, towards the heart, matches a vein.
- The thin wall is enough because the pressure is low.
Full answer: “R is a vein. It has valves to stop the low-pressure blood flowing backwards, and a thin wall because it does not need to withstand high pressure.”
The mistake that loses marks
Students write “arteries carry oxygenated blood” as a defining feature. It is true for most arteries, but the pulmonary artery carries deoxygenated blood.
| Student writes | Problem | Better |
|---|---|---|
| Arteries carry oxygenated blood | Not true for the pulmonary artery | Arteries carry blood away from the heart |
| Veins have a thin wall | Stops at the fact | Veins have a thin wall because pressure is low |
| Capillaries are small | Too vague | Capillary walls are one cell thick so diffusion is fast |
Check yourself
A student examines two vessels. Vessel A has a thick wall with a narrow lumen. Vessel B has a wide lumen and valves. State which is the artery and give one reason each for A and B.
Answer
A is the artery. Its thick wall withstands high pressure from the heart.
B is the vein. Its valves stop low-pressure blood flowing backwards.
What to study next
Next, explaining blood components and transport shows what travels through these vessels. Check your comparisons on the transport in humans and animals practice set.
If comparison tables still need rote memory, a teacher can rebuild them from reasons with you. See online one-to-one Biology tuition.