9700 · 8.3
The heart flashcards
Revision flashcards for Cambridge 9700 The heart (syllabus 8.3). Flip, recall, then mark a real past-paper question.
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What does it mean for cardiac muscle to be myogenic?
Myogenic means the muscle can contract and relax rhythmically on its own, without any stimulation from the nervous system. The heart's intrinsic conduction system initiates each beat.
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What is the role of the sinoatrial node (SAN)?
The SAN, located in the wall of the right atrium, acts as the heart's natural pacemaker. It generates electrical impulses that spread across the atria, causing them to contract.
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Why is there a delay in the impulse at the atrioventricular node (AVN)?
The AVN introduces a crucial delay (approx. 0.1 seconds) before passing the impulse to the ventricles. This ensures the atria have finished contracting and have completely emptied their blood into the ventricles before the ventricles begin to contract.
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Trace the path of deoxygenated blood through the right side of the heart.
Vena Cava → Right Atrium → (through Tricuspid Valve) → Right Ventricle → (through Pulmonary Valve) → Pulmonary Artery → Lungs.
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Trace the path of oxygenated blood through the left side of the heart.
Pulmonary Veins → Left Atrium → (through Bicuspid/Mitral Valve) → Left Ventricle → (through Aortic Valve) → Aorta → Body.
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How does the structure of the aorta wall differ from the vena cava wall?
The aorta has a much thicker tunica media with more muscle and elastic fibres to withstand and maintain high blood pressure. The vena cava has a thinner wall, a wider lumen, and its thickest layer is the tunica externa.
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State two structural adaptations of a capillary for efficient exchange.
1. **Very thin wall:** It is only one cell thick (endothelium), minimizing the diffusion distance. 2. **Narrow lumen:** Forces red blood cells to pass in single file, slowing blood flow and maximizing time for diffusion.
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What is cardiac output and how is it calculated?
Cardiac output is the volume of blood pumped by one ventricle of the heart in one minute. It is calculated by the formula: Cardiac Output = Heart Rate × Stroke Volume.