The shape of the lesson
By the end of the lesson, learners can
- Two pumps, four chambers: Click each part of the heart: the atria, ventricles and septum, the two kinds of valve, the four vessels, then the SAN, AVN and Purkyne tissue.
- The cardiac cycle: pressure decides: Use the graph in the lab and Fig. 1.
- SAN, AVN, Purkyne tissue: Heart muscle is myogenic: it starts its own beat.
- Walls: atria thin; left ventricle thicker than right (body versus lungs).
- Valve rule: higher pressure behind opens it; higher pressure in front shuts it.
- Systole: AV shut, then SL open. Diastole: SL shut, then AV open.
- SAN starts; AVN delays about 0.1 s; Purkyne to the apex.
One picture every idea returns to
The heart has four chambers: thin-walled atria receive blood from the vena cava (right) and pulmonary vein (left) and pump it a short distance into the ventricles. The left ventricle has a thicker muscular wall than the right because it pumps blood at high pressure all round the body, while the right ventricle pumps only to the nearby lungs at lower pressure. The septum keeps oxygenated and deoxygenated blood apart. Atrioventricular valves stop backflow into the atria; semilunar valves stop backflow from the aorta and pulmonary artery. Valves open and close only because of pressure differences. In the cardiac cycle, atrial systole tops up the ventricles, ventricular systole closes the AV valves and opens the semilunar valves, and in diastole the semilunar valves close and the AV valves open as the heart refills. The sinoatrial node starts each wave of excitation, the atrioventricular node delays it, and the Purkyne tissue carries it to the apex so the ventricles contract from the bottom up.
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, Pressure opens the valves, the SAN sets the beat.. The mammalian heart is two pumps side by side. 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: Two pumps, four chambers | Click each part of the heart: the atria, ventricles and septum, the two kinds of valve, the four vessels, then the SAN, AVN and Purkyne tissue. Project tab 7 of the lab (Transport in mammals lab, heart and cardiac cycle) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: The cardiac cycle: pressure decides | Use the graph in the lab and Fig. 1. | Pairs |
| 21 to 30 min | Teach and check: SAN, AVN, Purkyne tissue | Heart muscle is myogenic: it starts its own beat. | Corners |
| 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, 23 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 SAN, AVN, Purkyne tissue, 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.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
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 |
|---|---|
| The ventricles have thicker walls than the atria because of the distance and resistance they pump against, not because they hold more blood. | Both ventricles pump the same volume per beat. |
| The AVN does not start the heartbeat; the SAN does. | The AVN's job is the delay. |
The heart and the cardiac cycle: worksheet
6 questions, 23 marks. Written in the style of the papers; no past paper question is reproduced.
Describe the internal structure of the mammalian heart.
Explain the differences in the thickness of the walls of the atria and ventricles, and of the left and right ventricles.
Explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne tissue in the cardiac cycle.
Describe the cardiac cycle, relating the pressure changes during systole and diastole to the opening and closing of the valves.
Use Fig. 1. State the time at which the semilunar valve opens and the time at which it closes, and calculate the percentage of the 0.8 s cycle during which blood is ejected into the aorta.
A person's heart rate rises from 70 to 120 beats per minute during exercise while each ventricle pumps 75 cm3 per beat. Calculate the cardiac output (volume pumped per minute by one ventricle) at each rate in dm3 min-1, and the percentage increase.
Answer key and marking notes
- Four chambers: two thin-walled atria above two thick-walled ventricles.
- A muscular septum separates the left side (oxygenated blood) from the right side (deoxygenated blood).
- Atrioventricular valves (tricuspid on the right, bicuspid on the left) lie between atria and ventricles, attached to tendons.
- Semilunar valves lie at the bases of the aorta (from the left ventricle) and pulmonary artery (from the right ventricle).
- Atria have thin walls because they pump blood only a short distance, into the ventricles, needing little pressure.
- Ventricles have thicker walls because they pump blood out of the heart into the arteries, against much greater resistance.
- The left ventricle wall is thicker than the right because it pumps blood at high pressure all round the body (systemic circulation).
- The right ventricle pumps only to the nearby lungs at lower pressure, which also avoids damaging the delicate lung capillaries.
- The SAN (pacemaker) sends out a wave of excitation across both atria, which contract (atrial systole).
- Non-conducting tissue stops the wave reaching the ventricles directly; the AVN picks it up and delays it (about 0.1 s).
- The delay lets the atria finish emptying blood into the ventricles before the ventricles contract.
- The Purkyne tissue carries the wave down the septum to the apex and up the ventricle walls, so the ventricles contract from the base upwards, pushing blood into the arteries.
- Atrial systole: atria contract; atrial pressure slightly above ventricular, so blood passes through the open AV valves into the ventricles.
- Ventricular systole: ventricular pressure rises above atrial pressure, so the AV valves close.
- When ventricular pressure exceeds pressure in the aorta and pulmonary artery, the semilunar valves open and blood is ejected.
- Diastole: ventricles relax; when their pressure falls below arterial pressure the semilunar valves close.
- When ventricular pressure falls below atrial pressure the AV valves open and the ventricles fill with blood returning from the veins.
- The semilunar valve opens at about 0.15 s, when left ventricular pressure rises above aortic pressure.
- It closes at about 0.40 s, when left ventricular pressure falls below aortic pressure.
- Ejection lasts about 0.25 s; 0.25 ÷ 0.8 × 100 = about 31% of the cycle.
- At rest: 70 × 75 = 5250 cm3 min-1 = 5.25 dm3 min-1.
- Exercise: 120 × 75 = 9000 cm3 min-1 = 9.00 dm3 min-1.
- Increase = 3.75 ÷ 5.25 × 100 = 71% (to 2 significant figures).
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 blood vessel brings blood into the left atrium?
- Apulmonary vein
- Bvena cava
- Cpulmonary artery
- Daorta
Which structure acts as the pacemaker of the heart?
- Asinoatrial node
- Batrioventricular node
- CPurkyne tissue
- Dseptum
During which part of the cardiac cycle are both the atrioventricular and the semilunar valves closed?
- Athe start of ventricular systole, before ejection
- Batrial systole, while the ventricles fill
- Cthe middle of ventricular systole, during ejection
- Dlate diastole, as blood flows into the ventricles
What prevents the wave of excitation passing directly from the atria to the ventricles?
- Aa layer of non-conducting tissue between atria and ventricles
- Bthe semilunar valves at the base of the arteries
- Cthe thick muscular wall of the left ventricle
- Dthe Purkyne tissue in the septum
A student cuts across the ventricles of a sheep heart. One ventricle has a wall about three times as thick as the other. Which ventricle is thicker, and why?
- Athe left, because it pumps blood around the whole body
- Bthe right, because it pumps blood to the lungs at high pressure
- Cthe left, because it holds a larger volume of blood
- Dthe right, because it receives blood from the vena cava
The graph shows pressure in the aorta and left ventricle during one cardiac cycle. At which point do the semilunar valves close?
- AQ
- BP
- CR
- DS
A heart beats 72 times per minute. Atrial systole lasts 0.10 s and ventricular systole lasts 0.30 s. What is the duration of diastole in each cycle?
- A0.43 s
- B0.83 s
- C0.40 s
- D0.53 s
In some people the AVN does not delay the wave of excitation. Suggest the most likely effect on the heart's pumping.
- Athe ventricles contract before the atria have emptied, so less blood is pumped per beat
- Bthe atria fail to contract, because no wave reaches them
- Cthe ventricles contract from the top downwards instead of from the apex
- Dthe heart stops beating, because the SAN can no longer fire
Quiz key
The pulmonary vein returns oxygenated blood from the lungs to the left atrium. The vena cava enters the right atrium. The pulmonary artery and aorta carry blood out of the ventricles.
The sinoatrial node in the right atrium starts each wave of excitation. The AVN delays the wave, the Purkyne tissue conducts it through the ventricles, and the septum is a wall that carries the Purkyne tissue but does not start the beat.
At the start of ventricular systole, ventricular pressure has risen above atrial pressure (AV valves shut) but not yet above aortic pressure (semilunar valves still shut), so the volume stays the same while pressure builds. During atrial systole and late diastole the AV valves are open; during ejection the semilunar valves are open.
A band of non-conducting fibrous tissue separates atria from ventricles, so the wave can only pass through the AVN. Valves are not part of the conducting system, the left ventricle wall conducts the wave rather than blocking it, and the Purkyne tissue carries the wave into the ventricles.
The left ventricle has the thicker wall because it must generate high pressure to push blood through the long, high-resistance systemic circulation. The right ventricle pumps to the lungs at lower pressure. Both ventricles hold and pump the same volume, and where a chamber receives blood from does not set its wall thickness.
At Q the falling ventricular pressure drops below aortic pressure, the semilunar valve snaps shut and a small notch appears in the aortic trace. At P ventricular pressure rises above aortic pressure, so the semilunar valve opens. R is atrial systole topping up the ventricle, and S is where ventricular pressure has fallen low enough for the AV valve to open.
One cycle lasts 60 ÷ 72 = 0.83 s. Diastole = 0.83 - 0.10 - 0.30 = 0.43 s. 0.83 s is the whole cycle, 0.40 s is the total time in systole, and 0.53 s subtracts only ventricular systole.
The delay lets the atria finish emptying into the ventricles. Without it, atria and ventricles contract almost together, the ventricles are not fully filled and less blood is pumped each beat. The SAN still fires and the atria still contract. The Purkyne tissue still sets the direction of ventricular contraction.
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.