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Arteries, veins and capillaries

Transport in animals · Blood vessels · note 1 of 1

Spec B9.3.1, B9.3.2Download all Blood vessels notes (PDF)Download all notes (PDF)3 pages

Arteries, veins and capillariesSpec B9.3.1, B9.3.2

In short

Arteries have thick walls for high pressure, veins have thin walls and valves, and capillaries are one cell thick for exchange of substances.

Structure of blood vessels
VesselWallLumenValves
ArteryThickNarrowNo
VeinThinWideYes
CapillaryOne cell thickVery narrowNo
Cross-sections of an artery with a thick wall of muscle and elastic fibres and a narrow lumen, a vein with a thin wall and a wide lumen, and a capillary with a wall one cell thick and a very narrow lumen, plus a vein cut lengthways showing a valve that lets blood flow only towards the heart. (opens full size in a new tab)
Arteries have thick walls, veins have a wide lumen and valves, capillaries have walls one cell thick. (The capillary is drawn much larger than its real size.)
Supplement (what this means)Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Structure related to pressure

Supplement (what this means)Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean
  • Arteries carry blood away from the heart at high pressure. Their thick walls, containing muscle and elastic fibres, withstand the pressure and stretch and recoil with each beat. The narrow lumen helps to maintain the pressure.
  • Veins carry blood back to the heart at low pressure. They need only thin walls, and the wide lumen gives little resistance to flow. Valves stop the blood flowing backwards.
Supplement (what this means)Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean
Exam tip:

Do not say that veins have 'no muscle'. Say their walls are thinner because the blood is at lower pressure.

Quick check

  1. Which blood vessels have valves?

    Show answer

    Veins.

  2. Supplement Why do arteries have thick walls?

    Show answer

    They carry blood at high pressure, so the walls must withstand it.

Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026

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