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2.7.1Additional lessons

Blood Vessels — IB Biology SL Revision Notes & Topical Questions

5 min read 5 parts Lesson 34 of 142

📚 IB Biology SL Hub / Topical Revision
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Part 1 of 5Types of Blood Vessel

Arteries
  • Arteries Carry blood away from the heart at high pressure, with thick walls and a narrow lumen.
Arterioles
  • Arterioles Small branches of arteries whose muscle controls how much blood reaches the capillary beds.
Capillaries
  • Capillaries Tiny vessels with walls one cell thick that form the exchange surface between blood and tissues.
Venules
  • Venules Small vessels that collect blood from capillaries and join into veins.
Veins
  • Veins Carry blood towards the heart at low pressure, with thinner walls, a wide lumen and valves.
FeatureArteryCapillaryVein
Wall thicknessThickOne cell thickThin
LumenNarrowVery narrowWide
ValvesNoNoYes
Blood pressureHighFallingLow

Part 2 of 5Adaptations

Adaptations
Artery wall
  • Artery wall Thick layers of elastic fibres and muscle withstand high pressure and recoil to keep blood flowing between heartbeats.
Capillary wall
  • Capillary wall A single layer of endothelium gives a short diffusion distance, and gaps in some capillaries let plasma leak out as tissue fluid.
Capillary lumen
  • Capillary lumen A lumen so narrow that red blood cells pass in single file slows flow and increases contact time for exchange.
Vein valves
  • Vein valves Valves prevent backflow of blood, while skeletal muscle contraction squeezes veins to push blood toward the heart.

Part 3 of 5Identifying Vessels and Pulse

1
In a micrograph, the thick wall and small lumen show an artery, whereas a thin wall and large lumen show a vein.
2
Arteries often appear round because their walls are strong, while veins often look collapsed or irregular.
3
The pulse is the stretch and recoil of arteries caused by each contraction of the left ventricle.
4
It is measured at the radial artery in the wrist or the carotid artery in the neck.
5
Counting pulses for 60 seconds, or for 30 seconds and doubling, gives the heart rate in beats per minute.

Part 4 of 5Worked Example

Question

  • A student counts 38 pulses in 30 seconds at the radial artery.
  • Calculate the pulse rate in beats per minute.

  1. The count was taken over 30 seconds, which is half a minute.
  2. Multiply the count by 2 to scale it to 60 seconds.
  3. 38 × 2 = 76.

Answer The pulse rate is 76 beats per minute.

Part 5 of 5Exam Checklist & Tips

2.7.1 – Key Points for the Exam

  • Artery A vessel that carries blood away from the heart.
  • Vein A vessel that carries blood towards the heart.
  • Capillary A very small vessel where exchange between blood and tissues occurs.
  • Lumen The central space inside a blood vessel.
  • Tissue fluid Fluid that leaks from capillaries and surrounds the cells, enabling exchange.

Common Mistakes

  • Assuming arteries always carry oxygenated blood; the pulmonary artery carries deoxygenated blood.
  • Saying veins have thick muscular walls; their walls are thin.
  • Forgetting that valves occur in veins and not in arteries.
  • Saying capillaries have valves or thick walls, when their walls are a single cell thick.

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