The heart, cardiac cycle & double circulation
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Question
What are the four chambers of the heart?
Answer
Two **atria** (upper, thin-walled, receive blood) and two **ventricles** (lower, thick-walled, pump blood out).
Question
What is the job of an atrium?
Answer
An **atrium** receives blood from the veins and passes it down into a **ventricle**. Atria have thin walls.
Question
What is the job of a ventricle?
Answer
A **ventricle** pumps blood out into an artery. Ventricles have thick, muscular walls.
Question
Which chamber has the thickest wall, and why?
Answer
The **left ventricle** — it pumps blood to the **whole body** at high pressure, so it needs the most muscle.
Question
Which side of the heart carries deoxygenated blood?
Answer
The **right side** — it receives deoxygenated blood from the body and pumps it to the **lungs**.
Question
Which side of the heart carries oxygenated blood?
Answer
The **left side** — it receives oxygenated blood from the lungs and pumps it to the **body**.
Question
What is the cardiac cycle?
Answer
One complete heartbeat: the repeating sequence of **contraction (systole)** and **relaxation (diastole)** of the heart chambers.
Question
What are the three stages of the cardiac cycle?
Answer
**Atrial systole** (atria contract), **ventricular systole** (ventricles contract) and **diastole** (chambers relax and refill).
Question
What causes the two heart sounds ('lub-dub')?
Answer
Valves shutting: **'lub'** = the AV valves closing, **'dub'** = the semilunar valves closing.
Question
When does a heart valve open?
Answer
When the pressure **behind** it becomes **higher** than the pressure **in front** of it.
Question
What is double circulation?
Answer
Blood passes through the heart **twice** per body circuit — once for the **lungs** (pulmonary circuit) and once for the **body** (systemic circuit).
Question
Why is double circulation an advantage?
Answer
The heart **re-pressurises** blood after the lungs, so the body receives **high-pressure** blood, and oxygenated and deoxygenated blood stay **separate**.
Question
Trace deoxygenated blood from the body to the lungs.
Answer
Vena cava → **right atrium** → **right ventricle** → **pulmonary artery** → lungs.
Question
Trace oxygenated blood from the lungs to the body.
Answer
Pulmonary vein → **left atrium** → **left ventricle** → **aorta** → body.
Question
Which vessels break the 'arteries carry oxygenated blood' rule?
Answer
The **pulmonary artery** (deoxygenated) and the **pulmonary vein** (oxygenated).
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