Heart Structure & Double Circulation

Activities to try

1. 1

   Drive the blood: tracing one drop through two loops

   Why it works: Double circulation is a routing process: blood passes through the heart twice per full circuit, and the heart re-pressurises it between the lung loop and the body loop so it reaches the body at high pressure after being oxygenated. Valves prevent backflow; the pumping force comes from heart muscle, not valves.

   1. Pump the heart and follow one blood drop all the way round, starting from the body: body → vena cava → right atrium → right ventricle → to the lungs → left atrium → left ventricle → aorta → back to the body.
   2. Watch (or mark, on paper) the drop's oxygenation change: it loads oxygen in the lungs (deoxygenated → oxygenated) and unloads it as body cells use it (oxygenated → deoxygenated) — note that colour represents oxygenation state, not literally blue blood.
   3. Try to push blood backwards through a valve and observe that a valve blocks it.
   4. Compare the two circuits with a 'single circulation' model version: route blood straight from the lungs to the body without an intermediate return to the heart, and describe what happens to its speed and pressure by the time it reaches the body.
   5. State in one sentence WHY mammals use a double circuit, referring to the heart re-pressurising blood between the lung loop and the body loop.
2. 2

   Heart anatomy: chambers, valves and vessels in three dimensions

   Why it works: Structure follows function: the four-chambered pump is spatially arranged so the two sides stay separate (septum), and the thicker left ventricle wall matches the greater pumping demand of the whole-body loop.

   1. Examine and rotate a manipulable heart model (a rotatable screen model, or a real sheep/pig heart), identifying the four chambers, valve positions and the great vessels in their spatial arrangement.
   2. Cross-section the heart to compare the thickness of the left ventricle wall against the right ventricle and the atria.
   3. Explain why the left ventricle wall is thickest by linking it to its job: pumping blood the whole way round the body.
   4. Locate the septum and state what it does: keeps the oxygenated (left) and deoxygenated (right) blood from mixing in a healthy heart.
   5. Label a diagram with atria, ventricles, valves, aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries.
3. 3

   Which way does water pass? Predict–observe with a valve

   Why it works: Valves are passive one-way gates that prevent backflow; they are opened and closed by the pressure of blood the muscle moves, not a source of pumping themselves.

   1. Before pouring, PREDICT which direction water will pass freely through a one-way valve model (or a valve in a fresh sheep/pig heart) and which direction will be blocked, and explain why.
   2. Pour water through the valve in each direction and OBSERVE which way flows and which way is stopped.
   3. Reconcile prediction with observation, stating in your own words what the valve does and what it does NOT do (it does not pump).
   4. Discuss: if a valve became leaky, what problem would that cause, and why is that different from the pump (muscle) failing?