The shape of the lesson
By the end of the lesson, learners can
- One heart, two circuits: Click each vessel in the model: pulmonary artery, pulmonary vein, aorta and vena cava, then the arterioles, capillaries and venules.
- A wall for every pressure: Choose the elastic artery, muscular artery, vein and capillary in turn, then click each layer.
- Recognising and drawing vessels: On slides, photomicrographs and electron micrographs, decide which vessel is which from the wall and the lumen, then draw plan diagrams.
- Closed: blood stays in vessels. Double: through the heart twice per circuit.
- Arteries carry blood away from the heart; veins carry it back.
- Elastic artery: stretch and recoil. Muscular artery: control flow.
- Vein: thin wall, wide lumen, valves. Capillary: one cell thick.
One picture every idea returns to
The mammalian circulatory system is a closed double circulation made of a heart, blood and blood vessels: arteries, arterioles, capillaries, venules and veins. Closed means the blood stays inside vessels. Double means it passes through the heart twice per complete circuit: the pulmonary circulation (right ventricle, pulmonary artery, lungs, pulmonary vein, left atrium) and the systemic circulation (left ventricle, aorta, body, vena cava, right atrium). Elastic arteries near the heart stretch and recoil to smooth the flow; muscular arteries have thick smooth muscle to control flow to organs; veins carry low-pressure blood in a wide lumen with thin walls and valves; capillaries have walls one endothelial cell thick for rapid exchange.
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, Twice through the heart, never out of a vessel.. Mammals have a closed double circulation: blood goes through the heart once on its way to the lungs and again on its way to the body. 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: One heart, two circuits | Click each vessel in the model: pulmonary artery, pulmonary vein, aorta and vena cava, then the arterioles, capillaries and venules. Project tab 1 of the lab (Transport in mammals lab, double circulation) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: A wall for every pressure | Choose the elastic artery, muscular artery, vein and capillary in turn, then click each layer. Project tab 2 of the lab (Transport in mammals lab, blood vessels) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Recognising and drawing vessels | On slides, photomicrographs and electron micrographs, decide which vessel is which from the wall and the lumen, then draw plan diagrams. | Think-Pair-Share |
| 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 Recognising and drawing 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.
Think-Pair-Share
Pose the question, give thirty seconds of silent thinking, then a minute to compare with a partner before a few pairs share with the class. The silent minute is the part that cannot be cut.
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 |
|---|---|
| Arteries carry blood away from the heart and veins carry blood towards it. | Do not define them by oxygen: the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood. |
| An artery has a small lumen relative to its thick wall; a vein has a wide lumen and often looks squashed or irregular on a slide because its thin wall does not hold its shape. | Return to A wall for every pressure: ask a pair to state the correct version and show it on the lab before moving on. |
A closed double circulation and its blood vessels: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
State what is meant by describing the mammalian circulatory system as a closed double circulation.
Describe the functions of the pulmonary artery, pulmonary vein, aorta and vena cava.
Explain how the structure of a capillary is related to its function.
Explain the differences between the walls of a muscular artery and a vein in terms of their functions.
The mean blood pressure in the aorta is about 13 kPa, while in the vena cava near the heart it is below 1 kPa. Suggest why the wall of the aorta contains a large amount of elastic tissue but the wall of the vena cava does not.
On a photomicrograph at ×100, a vessel has a lumen 0.8 mm wide on the image and a wall 0.6 mm thick on the image. A second vessel has a lumen 4.0 mm wide and a wall 0.3 mm thick. Calculate the actual lumen width of the first vessel in μm and identify each vessel, giving a reason.
Answer key and marking notes
- Closed: the blood remains inside blood vessels (and the heart) at all times.
- Double: the blood passes through the heart twice in one complete circuit of the body.
- There is a pulmonary circulation (heart to lungs and back) and a systemic circulation (heart to body and back).
- Pulmonary artery: carries deoxygenated blood from the right ventricle to the lungs.
- Pulmonary vein: carries oxygenated blood from the lungs to the left atrium.
- Aorta: carries oxygenated blood at high pressure from the left ventricle to the body (systemic circulation).
- Vena cava: returns deoxygenated blood from the body to the right atrium.
- The wall is a single layer of thin, flattened endothelial cells, so the diffusion distance is short.
- Gaps between the endothelial cells let fluid and small solutes leave to form tissue fluid.
- The narrow lumen means red blood cells pass in single file, close to the wall, and flow slowly, giving time for exchange.
- Capillaries are very numerous and branched, giving a large surface area close to every cell.
- The muscular artery has a thick tunica media of smooth muscle; the vein has a thin tunica media with little muscle.
- The artery's muscle contracts or relaxes to change the lumen diameter and control blood flow to organs, and the thick wall withstands high pressure.
- Blood in a vein is at low pressure, so a thick wall is not needed; the wide lumen reduces resistance to flow.
- Veins have valves to prevent backflow of low-pressure blood; arteries do not need them.
- The aorta receives blood in surges at high pressure each time the left ventricle contracts.
- Elastic fibres stretch to absorb the surge, then recoil to push blood on and maintain pressure between beats, giving a smoother flow.
- In the vena cava the pressure is low and steady, so there are no surges to absorb and little elastic tissue is needed.
- Actual lumen width = 0.8 mm ÷ 100 = 0.008 mm = 8 μm.
- First vessel: wall thick relative to its small lumen, so it is an artery (here a small artery or arteriole).
- Second vessel: thin wall relative to a wide lumen, so it is a 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.
Which list contains only vessels found in the mammalian circulatory system, in the order blood passes through them after leaving the heart?
- Aartery, arteriole, capillary, venule, vein
- Bartery, venule, capillary, arteriole, vein
- Carteriole, artery, capillary, vein, venule
- Dartery, capillary, arteriole, venule, vein
The diagram shows the double circulation, viewed from the front. Which labelled vessel is the pulmonary vein?
- AX
- BW
- CY
- DZ
Which vessel carries blood at the highest pressure?
- Aaorta
- Bpulmonary artery
- Cvena cava
- Dpulmonary vein
A student says that arteries always carry oxygenated blood and veins always carry deoxygenated blood. Which vessel shows the student is wrong?
- Athe pulmonary artery
- Bthe aorta
- Cthe vena cava
- Dthe renal vein
Which feature of a vein helps blood return to the heart at low pressure?
- Avalves that prevent blood flowing backwards
- Ba thick layer of elastic fibres that recoils
- Ca thick layer of smooth muscle that contracts rhythmically
- Da wall only one cell thick
The table shows measurements from transverse sections of three vessels. Which row is most likely to be a muscular artery?
- AP, because its wall is thick relative to its lumen and it has no valves
- BQ, because it has the widest lumen to carry the most blood
- CR, because its very thin wall allows rapid control of flow
- DQ, because its valves control the flow to each organ
Blood pressure in the aorta varies between about 10 kPa and 16 kPa during each heartbeat, but in the arterioles the pressure hardly varies. Which explanation is correct?
- Aelastic recoil of artery walls evens out the surges before blood reaches the arterioles
- Bvalves in the arteries close between beats, holding the pressure constant
- Cthe arterioles contract and relax in time with each heartbeat
- Dblood is pumped into the arterioles by the right ventricle at a steady rate
Fish have a single circulation: blood passes from the heart to the gills, then straight on to the body. Suggest the main disadvantage of this compared with a mammal's double circulation.
- Ablood reaches the body at low pressure after losing pressure in the gill capillaries
- Boxygenated and deoxygenated blood mix in the ventricle
- Cblood passes through the heart twice in each circuit
- Dthe gills receive blood at too high a pressure to exchange gases
Quiz key
Arteries branch into arterioles, which feed capillaries; capillaries join into venules, which join into veins. The second and third options swap the small vessels with the wrong large vessels, and the fourth puts the arteriole after the capillary bed, where venules belong.
X runs from the lungs to the heart on the right of the diagram, which is the left side of the heart: the pulmonary vein. W leaves the right side of the heart for the lungs (pulmonary artery). Y leaves the left side for the body (aorta). Z returns from the body to the right side (vena cava).
The aorta receives blood from the left ventricle, which generates the highest pressure to supply the whole body. The pulmonary artery leaves the right ventricle at a lower pressure. The vena cava and pulmonary vein return blood to the heart at low pressure.
The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, so not every artery carries oxygenated blood. The aorta (oxygenated), vena cava (deoxygenated) and renal vein (deoxygenated) all fit the student's rule. Arteries are defined by carrying blood away from the heart.
Pocket valves close if blood starts to flow backwards, so squeezing by skeletal muscles can only move blood towards the heart. Thick elastic and muscle layers belong to arteries, and veins do not pump rhythmically. A wall one cell thick describes a capillary.
P has a wall half as thick as its lumen is wide and no valves: a thick muscular wall around a small lumen, typical of a muscular artery. Q has a thin wall, a wide lumen and valves, so it is a vein; its valves prevent backflow rather than control supply. R, with a lumen of 8 μm and a wall 0.5 μm thick, is a capillary, which has no muscle to control flow.
Elastic fibres stretch during systole, absorbing part of each surge, and recoil during diastole, pushing blood on; this, with resistance in the small arteries, smooths the flow so the pressure barely fluctuates in arterioles. Arteries have no valves along their length. Arterioles do not pulse with each beat; their muscle sets their diameter. The right ventricle supplies the lungs, not the systemic arterioles.
Pressure falls greatly in capillary beds, so after the gills blood moves slowly to the body, limiting how fast oxygen can be delivered. A mammal returns blood to the heart after the lungs to repressurise it. In a fish heart only deoxygenated blood passes through, so there is no mixing. Passing through the heart twice describes double circulation. Gill pressure is not too high; the issue is the loss afterwards.
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.