Lesson overview
Blood vessels: Why are arteries, veins and capillaries built so differently?
Under a microscope, decide which of two vessels cut across is the artery, then measure the wall and the lumen (the space inside) of each to compare them. Then watch a vein’s valve at work and look at capillaries at ×400, the vessels where substances pass to and from the cells.
Suggested sequence
- Lesson 1 · Artery or vein? Artery or vein? Walls, lumens and valves, and how they suit the pressure of the blood. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Capillaries. Capillaries: walls one cell thick, where substances are exchanged with the cells. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · The main blood vessels. The main blood vessels to and from the heart, lungs, kidneys and liver. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- End of module · final check. 6 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 7 questions, 15 min, lesson closed.
Learning goals
Part 1: Artery or vein?
- Describe the structure of arteries and veins, limited to: relative thickness of wall, diameter of the lumen and the presence of valves in veins (9.3.1)
- Supplement: explain how the structure of arteries and veins is related to the pressure of the blood that they transport (S9.3.4)
Part 2: Capillaries
- Describe the structure of capillaries, limited to: relative thickness of wall and diameter of the lumen (9.3.1)
- State the functions of capillaries (9.3.2)
- Supplement: explain how the structure of capillaries is related to their functions (S9.3.5)
Part 3: The main blood vessels
- Identify in diagrams and images the main blood vessels to and from the heart (vena cava, aorta, pulmonary artery, pulmonary vein), the lungs (pulmonary artery, pulmonary vein) and the kidney (renal artery, renal vein) (9.3.3)
- Supplement: identify in diagrams and images the main blood vessels to and from the liver: hepatic artery, hepatic veins and hepatic portal vein (S9.3.6)
Misconceptions to listen for
- “An artery has a thinner wall, so blood can be pushed through it easily.” — It is the other way round: the artery on the slide had a wall about as thick as its lumen was wide; the vein's wall was thin.
- “R is an artery, because it is round and small.” — Size and shape do not decide it. R's wall is one flattened cell thick, with no muscle: it is a capillary, drawn much larger than it really is.
- “Valves are found in arteries, to stop blood flowing back into the heart.” — Along their length, arteries have no valves. The valves along a vessel's length are in veins.
- “The thick wall stops oxygen leaking out of the blood.” — Exchange happens in capillaries, not arteries. The thick wall is about pressure.
- “The elastic tissue pumps the blood like a second heart.” — It only stretches and springs back; it smooths the flow the heart makes. The muscle in the wall can narrow or widen the artery.
- “Wall ÷ lumen is 1.0 µm.” — Both lengths are in µm, so the units cancel: the answer is a number with no unit.
- “The wall thickness is 600 µm.” — That adds both sides. The wall on each side is one wall: take the mean of the two.
- “Arteries carry oxygenated blood and veins deoxygenated blood.” — That is not a difference in structure, and it is not always true: the pulmonary artery carries deoxygenated blood.
- “The pressure in the veins is so high that valves are needed to slow the blood down.” — Read the graph: the veins have the lowest pressure of all. Valves stop low-pressure blood flowing back.
- “A vein has a thin wall so that substances can diffuse through it.” — A vein's wall is still far too thick for exchange; exchange happens in capillaries. The thin wall fits the low pressure.
Scope
Blood vessels (9.3.1–9.3.6): the structure of arteries, veins and capillaries (relative thickness of the wall, diameter of the lumen, valves in veins), the functions of capillaries and the main blood vessels to and from the heart, lungs and kidneys; for the Supplement, how the structure of arteries and veins relates to the pressure of their blood, how the structure of capillaries relates to their functions, and the vessels to and from the liver. The heart itself is in “The heart and double circulation” and the blood’s cells and plasma are in “Blood”; lymph is not covered.