Human Anatomy and Physiology, with Emphasis on the Cardiovascular System
Human Anatomy and Physiology
This domain tests organ systems, with emphasis on the heart and circulation. ECG interpretation depends on knowing which chamber is depolarising and how the signal spreads.
Core rules
- The right atrium receives superior and inferior vena cava blood; the right ventricle pumps to the pulmonary artery. The left atrium receives pulmonary veins; the left ventricle pumps to the aorta.
- Valves: tricuspid between right atrium and ventricle; pulmonary valve at right ventricular outflow; mitral between left atrium and ventricle; aortic valve at left ventricular outflow.
- Conduction: SA node, AV node, bundle of His, bundle branches, Purkinje fibres. The SA node normally fires at 60-100/min.
- The left ventricular wall is thickest because it opposes systemic arterial pressure.
Worked example
Why does the left ventricle have a thicker wall than the right? It pumps blood into the aorta and systemic circulation, where pressure is much higher. The right ventricle pumps into the low-pressure pulmonary circulation. Greater sustained pressure requires more muscle mass, so the left ventricle is normally thicker.
Traps that cost marks
The pulmonary artery carries deoxygenated blood, while pulmonary veins carry oxygenated blood. Atria receive blood; ventricles pump it out. Do not say the AV node is the primary pacemaker, because the SA node normally dominates. ECG P waves reflect atrial depolarisation, not atrial contraction itself.