The shape of the lesson
By the end of the lesson, learners can
- Artery, vein, capillary: Switch between artery, vein and capillary.
- What capillaries do: Capillaries are where the circulatory system does its real work.
- The main vessels: Click a vessel name or the vessel itself to light it up and watch the blood flow along it.
- Arteries: away from the heart; thick muscular, elastic wall; narrow lumen; high pressure.
- Veins: back to the heart; thin wall; wide lumen; valves; low pressure.
- Capillaries: wall one cell thick; exchange with the tissues.
- Organ vessels: pulmonary (lungs), renal (kidneys), hepatic (liver, Extended); the hepatic portal vein comes from the gut.
One picture every idea returns to
Arteries have thick walls and a narrow lumen; veins have thin walls, a wide lumen and valves; capillaries have walls only one cell thick and a very narrow lumen. Capillaries exchange substances between the blood and the tissues. The main vessels are the vena cava, aorta, pulmonary artery and pulmonary vein (heart and lungs) and the renal artery and renal vein (kidneys).
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Thick walls for high pressure.. Arteries, veins and capillaries are three kinds of tube with three different jobs, and each one's shape fits the pressure of the blood inside it. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Artery, vein, capillary | Switch between artery, vein and capillary. Project tab 5 of the lab (Arteries, veins and capillaries) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: What capillaries do | Capillaries are where the circulatory system does its real work. | Pairs |
| 21 to 30 min | Teach and check: The main vessels | Click a vessel name or the vessel itself to light it up and watch the blood flow along it. Project tab 6 of the lab (Main blood vessels of the body) and let a student drive it while the class predicts. | Jot Thoughts |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 21 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in The main vessels, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Jot Thoughts
Teams write ideas on slips, one idea per slip, as many as they can in two minutes, saying each aloud as they place it in the middle. Then they sort the slips, which is where the structure of the topic appears.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Do not say arteries carry oxygenated blood and veins carry deoxygenated blood. | The definition is direction: arteries carry blood away from the heart and veins carry it back. The pulmonary artery carries deoxygenated blood. |
| "Capillaries are thin" is too vague. | Say the wall is one cell thick, so the diffusion distance is short. The lumen is narrow, which is a different point. |
| The hepatic portal vein runs from the gut to the liver, not from the liver to the heart. | Blood leaves the liver in the hepatic vein. |
Blood vessels: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
Describe three differences between the structure of an artery and a vein.
State the functions of capillaries.
Extended. Explain how the structure of arteries and veins is related to the pressure of the blood they carry.
Extended. Explain how the structure of capillaries is related to their function.
The table shows the mean blood pressure in different vessels.
| Vessel | Mean pressure / kPa |
|---|---|
| aorta | 13.0 |
| small artery | 11.5 |
| capillary | 3.5 |
| small vein | 1.6 |
| vena cava | 0.5 |
(a) Describe the trend shown. (b) Between which two vessels is the largest fall in pressure? (c) Use the data to explain why veins have valves.
Name the blood vessel that (a) carries blood from the lungs to the heart, (b) carries blood from the kidney, (c) carries blood from the aorta to the kidney, (d) (Extended) carries blood from the liver towards the heart.
Answer key and marking notes
- Arteries have a thicker wall than veins.
- Arteries have a narrower lumen than veins (relative to the vessel size).
- Veins have valves; arteries do not (apart from where they leave the heart). (Also accept: arteries have more muscle and elastic tissue.)
- They carry blood close to every cell of the tissues.
- They are where substances are exchanged between blood and cells: oxygen and glucose move out to the cells, carbon dioxide and urea move into the blood.
- Arteries carry blood at high pressure, straight from the heart, so they need a thick wall to withstand the pressure without bursting.
- Elastic tissue in the artery wall stretches and recoils with each heartbeat, smoothing the flow; muscle and a narrow lumen keep the pressure high.
- Veins carry blood at low pressure, so their walls can be thin; the wide lumen gives little resistance to flow.
- Because the pressure is low, valves are needed in veins to prevent blood flowing backwards.
- The wall is one cell thick, giving a short diffusion distance between blood and cells.
- The wall is permeable, so substances such as glucose, oxygen and urea can pass through.
- Capillaries are very narrow and highly branched, so every cell is close to one and there is a large total surface area for exchange.
- Blood flows slowly and red blood cells pass in single file, giving time for exchange.
- (a) The pressure falls continuously as blood moves from the aorta, through the arteries and capillaries, to the veins and vena cava.
- (b) Between the small artery and the capillary (a fall of 8.0 kPa).
- (c) In the veins the pressure is very low (1.6 to 0.5 kPa), too low to keep the blood moving reliably towards the heart.
- Valves close if blood starts to flow backwards, so blood only moves towards the heart.
- (a) pulmonary vein.
- (b) renal vein.
- (c) renal artery.
- (d) hepatic vein.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
The diagram shows cross-sections of three blood vessels, not to scale. Which row identifies them correctly?
- AA vein, B artery, C capillary
- BA artery, B vein, C capillary
- CA capillary, B artery, C vein
- DA vein, B capillary, C artery
What is the main function of capillaries?
- AExchanging substances between the blood and the tissues
- BCarrying blood at high pressure away from the heart
- CReturning blood to the heart through valves
- DPumping blood through the organs of the body
Which blood vessel carries blood from the lungs to the heart?
- Apulmonary vein
- Bpulmonary artery
- Cvena cava
- Daorta
How does the blood in the renal vein differ from the blood in the renal artery?
- AIt contains less urea
- BIt contains more urea
- CIt contains more oxygen
- DIt is at a higher pressure
Which blood vessel carries deoxygenated blood away from the heart?
- Apulmonary artery
- Bpulmonary vein
- Caorta
- Dvena cava
(Extended) Why do veins need valves but most arteries do not?
- ABlood in veins is at low pressure, so it could flow backwards
- BBlood in veins is at high pressure, so it must be slowed down
- CVeins have thick walls that would otherwise collapse
- DVeins carry deoxygenated blood, which flows more slowly
(Extended) An hour after a meal rich in starch, in which blood vessel would the glucose concentration be highest?
- Ahepatic portal vein
- Bhepatic vein
- Chepatic artery
- Drenal vein
(Extended) Red blood cells pass through capillaries in single file, close to the capillary wall. How does this help the capillary carry out its function?
- AOxygen has only a short distance to diffuse to the tissues
- BThe cells push the capillary wall outwards to keep it open
- CThe blood flows faster, so more oxygen is delivered per second
- DThe cells leave the capillary and enter the tissue fluid
Quiz key
A has a thin wall and a wide lumen, so it is a vein. B has a thick wall and a narrow lumen, so it is an artery. C is tiny, with a wall one cell thick, so it is a capillary. Swapping A and B mixes up the thick-walled artery with the thin-walled vein, and the capillary is never the largest vessel.
Capillaries carry blood close to every cell and are where oxygen, glucose and other substances pass out to the tissues while carbon dioxide and urea pass in. Carrying high-pressure blood away from the heart is the job of arteries, and returning blood with the help of valves is the job of veins. No vessel pumps blood; the heart does that.
The pulmonary vein carries oxygenated blood from the lungs to the left atrium. The pulmonary artery carries blood the other way, from the heart to the lungs. The vena cava brings blood from the rest of the body, and the aorta carries blood from the heart to the body.
The kidneys filter the blood and remove urea, so blood leaving in the renal vein has less urea than blood arriving in the renal artery. Urea is removed, not added. The kidney cells use oxygen for respiration, so the renal vein has less oxygen, and as in all veins its pressure is lower than in the artery.
The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. It is an artery because it carries blood away from the heart, even though the blood is deoxygenated. The pulmonary vein carries oxygenated blood to the heart, the aorta carries oxygenated blood away from the heart, and the vena cava carries deoxygenated blood towards the heart.
By the time blood reaches the veins most of its pressure has been lost in the capillaries, so it could flow backwards; valves close to prevent this. Arteries carry high-pressure blood straight from the heart, which keeps it moving forwards. Vein blood is at low pressure, not high, and veins have thin walls, not thick. The oxygen content of blood does not decide whether it needs valves.
Starch is digested to glucose, which is absorbed into the blood in the small intestine and carried straight to the liver in the hepatic portal vein, so its glucose concentration is highest. The liver stores some of the excess glucose, so the hepatic vein leaving the liver has less. The hepatic artery and renal vein carry blood that has already been through the general circulation and has a normal glucose level.
With the red blood cells pressed close to a wall only one cell thick, oxygen released from haemoglobin has a very short distance to diffuse to the tissue cells. The cells do not hold the wall open. Blood flows slowly in capillaries, which gives more time for exchange. Red blood cells stay inside the capillaries; only the oxygen they carry leaves.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.