The heart
Introduced| English | Meaning |
|---|---|
| atria/ˈeɪtrɪə/ | Thin walls (push blood down). |
| ventricle/ˈventrɪkl/ | One of the lower chambers of the heart that pumps blood into an artery. |
| cardiac cycle/ˈkɑːdiæk ˈsaɪkl/ | One complete sequence of contraction and relaxation of the heart. |
| systole/ˈsɪstəʊl/ | The contraction phase of a heart chamber's cycle. |
| diastole/ˈdaɪəstəʊl/ | The relaxation phase of a heart chamber's cycle, during which it can fill with blood. |
| sinoatrial node/sɪˈnəʊtrɪəl nəʊd/ | A group of specialised cells in the right atrium that normally initiates the heart's electrical rhythm. |
| pacemaker/ˈpeɪsmeɪkə/ | A region of specialised cardiac cells that generates impulses setting the heart's rhythm. |
| atrioventricular node/ˌeɪtrɪˌəʊvənˈtrɪkjʊlə nəʊd/ | A group of specialised cells that delays and conducts electrical excitation from the atria toward the ventricles. |
| Purkyne tissue/ˈpɜːkaɪn ˈtɪʃuː/ | Specialised conducting fibres that rapidly spread electrical excitation through the ventricular walls. |
The pump that never rests
- The heart is a double pump with four chambers.
- Its walls are thicker where it must push blood further.
- And it sets its own rhythm — no outside command needed.
Structure
- The two upper chambers are the atria 心房 — thin walls, because they only push blood down into the chambers below.
- The two lower chambers are the ventricles 心室 — thick muscular walls, because they pump blood out of the heart.
- The left ventricle wall is the thickest: it pumps blood all the way round the body (the right side only reaches the nearby lungs).
The internal structure of the human heart
Explore the heart
Tap each part. The right side pumps blood to the lungs; the thicker-walled left side pumps it round the whole body.
Ventricles have thicker walls than atria because they:
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Atria only push blood into the ventricles below; ventricles pump blood out, so need thick muscular walls.
The thickest, most muscular chamber, which pumps blood around the whole body, is the left ______.
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The left ventricle drives the systemic circulation (whole body), so it needs the most muscle.
The cardiac cycle 心动周期
- One heartbeat is the cardiac cycle: systole 收缩期 (muscle contracts) and diastole 舒张期 (relaxes and fills).
- When a chamber contracts, the pressure inside rises.
- These pressure changes open and close the valves, so blood flows one way only.
Pressure rises and falls in the atria, ventricles and aorta through one cardiac cycle, working the valves
The cardiac cycle
Step through one heartbeat — atria contract, then ventricles contract, then everything relaxes and refills.
In the cardiac cycle, systole is when the heart muscle:
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Systole = contraction (pressure rises); diastole = relaxation and filling.
Match each stage of the cardiac cycle.
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Atria contract first, then ventricles, then everything relaxes; the valves keep blood moving one way.
The semilunar valves stop blood flowing back into the ventricles from the arteries.
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When the ventricles relax, the semilunar valves (in the aorta and pulmonary artery) shut to stop backflow.
Controlling the heartbeat
- The sinoatrial node 窦房结 (SAN) in the right atrium is the pacemaker 起搏点 — its wave of excitation makes the atria contract.
- The atrioventricular node 房室结 (AVN) picks up the wave and delays it (so the atria empty first).
- The Purkyne tissue 浦肯野组织 carries the wave down and up the ventricle walls, so the ventricles contract from the bottom up.
The heart's electrical conduction system
The pacemaker that sets the heart's rhythm is the:
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The SAN in the right atrium generates the wave of excitation that triggers each heartbeat.
Put the electrical conduction pathway in the correct order.
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SAN (pacemaker) → AVN (delay) → Purkyne tissue (ventricles contract from the bottom up).
You've got it
- atria = thin walls (push blood down); ventricles = thick walls (pump out)
- left ventricle is thickest — it pumps to the whole body
- cardiac cycle = systole (contract) + diastole (relax/fill); pressure works the valves (one-way flow)
- rhythm: SAN (pacemaker) → atria; AVN (delay) → Purkyne → ventricles contract bottom-up