Distinguish arteries and veins by direction
Follow heart connections while keeping oxygen content separate from vessel names.
Section B9.2 · Heart
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall pulmonary and systemic routes.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which direction defines a vein?
What you will learn
- Arteries carry blood away from the heart
- The pulmonary route shows the oxygen exceptions
Arteries carry blood away from the heart
An artery carries blood away from the heart. A vein carries blood towards the heart. The definition uses direction, not the amount of oxygen. In the normal adult systemic circuit the aorta carries oxygenated blood away, while the vena cava returns relatively deoxygenated blood.
Trace a complete mammalian route: vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta → body → vena cava. Repetition of vena cava marks return to the starting vessel.
The pulmonary route shows the oxygen exceptions
The pulmonary artery carries relatively deoxygenated blood from the right ventricle to the lungs. It is an artery because flow is away from the heart. The pulmonary vein carries oxygenated blood from the lungs to the left atrium, and is a vein because it returns to the heart.
An unfamiliar vessel is best classified from an arrow showing its heart connection. A red or blue colour may describe oxygen content but cannot replace the definition. All blood is red; colours in the route are diagram conventions. Detailed vessel-wall comparisons follow in the blood-vessel pathway.
Sources for this lesson
Pause and explain
Why is the pulmonary artery an artery?
Worked example
A vessel carries oxygen-rich blood from lungs to the heart. Is it an artery or vein?
Show the worked solution
- Direction is towards the heart.
- The lung-return vessel is the pulmonary vein.
Answer A vein: specifically a pulmonary vein, despite its oxygen-rich blood.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify heart → lungs and lungs → heart vessels.
Give me a hint
Use away and return directions.
Compare my reasoning
- Heart → lungs is pulmonary artery.
- Lungs → heart is pulmonary vein.
Pulmonary artery away; pulmonary vein towards the heart.
Look for these in your work
- Correct vessel names
- Use direction as the reason
State the oxygen content normally carried by pulmonary artery and pulmonary vein in the adult mammal model.
Give me a hint
Oxygen enters at the lungs.
Compare my reasoning
- Blood going to lungs is relatively deoxygenated.
- Blood returning from lungs is oxygenated.
Pulmonary artery: relatively deoxygenated. Pulmonary vein: oxygenated.
Look for these in your work
- Correct both oxygen states
- Retain the normal adult context
A new uncoloured diagram has a vessel with an arrow from the heart to an organ, but gives no oxygen data. What can you conclude?
Give me a hint
Separate a direction definition from missing composition evidence.
Compare my reasoning
- The arrow shows flow away from the heart.
- Without the organ identity or gas data, do not invent oxygen content.
It is an artery; oxygen content cannot be concluded from this arrow alone.
Look for these in your work
- Classify by direction
- Respect the missing oxygen evidence
Common mistakes
- Defining an artery as always oxygenated.
- Following colour without checking the arrow.
What can you explain now?
Why is the pulmonary artery an artery?
Compare with the explanation
It carries blood away from the heart
Its low oxygen content does not change the direction-based name.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the pulmonary exceptions to the oxygen shortcut in one sentence.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.