📖 Notes
LESSON 07 OF 16
Circulatory System — Heart, Blood & Vessels
The Circulatory System
The heart pumps blood through 100,000 km of vessels. Master cardiac anatomy, the cardiac cycle, and blood composition for MDCAT.
Heart Structure
4 Chambers, 4 Valves
4
Chambers: RA, RV, LA, LV
4
Valves: bicuspid, tricuspid, aortic & pulmonary SL
60–100
Normal heart rate (bpm)
100,000km
Total length of blood vessels
- Systole: contraction — blood pumped out
- Diastole: relaxation — heart fills
Blood Vessels
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Artery
Thick, elastic walls. Carries blood away from the heart.
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Vein
Thinner walls with valves. Carries blood to the heart.
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Capillary
One cell thick — the site of gas and nutrient exchange.
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Blood
55% plasma, 45% red blood cells, plus white blood cells and platelets.
Key Formulas
Cardiac Output & Blood Pressure
FORMULASCardiac Output = HR × Stroke Volume CO = 72 bpm × 70 mL ≈ 5 L/min Blood pressure: normal = 120/80 mmHg 120 = systolic (ventricle contracting) 80 = diastolic (ventricle relaxed) Haemoglobin: Hb + 4O2 ⇌ HbO2 Bohr effect: ↑CO2 → ↑O2 release to tissues
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Exam tip
The Bohr effect is a favourite MDCAT concept: rising CO2 lowers blood pH, which reduces haemoglobin's oxygen affinity — exactly what's needed to release more oxygen where tissues are working hardest.