BIOLOGY WITH HAMZA · MDCAT REVISION
Circulation
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Trace blood through the four chambers and two circuits.
- Explain valve opening and closure using pressure differences.
- Relate electrical conduction to atrial and ventricular contraction.
Core notes
- The right and left sides power pulmonary and systemic circuits.
- Pressure differences, not active valve movement, control one-way flow.
- The conduction system coordinates atrial then ventricular systole.
- Vessel structure reflects pressure, direction and exchange function.
Read, cover and redraw
Venae cavae return deoxygenated blood.
Pumps blood through the pulmonary artery.
Gas exchange oxygenates the blood.
Pumps blood through the aorta to the body.
Written recall
1. Why do semilunar valves close at the beginning of ventricular diastole?
2. Why is blood velocity low in capillaries despite their narrow individual diameter?
3. Can a contracting ventricle have both valves closed?
4. What prevents arterial backflow into a ventricle?
5. Are both circuits at the same pressure?
Apply the idea
1. A heart beats 75 times per minute with a stroke volume of 80 mL. What is its cardiac output?
- 6 L min⁻¹
- 0.6 L min⁻¹
- 60 L min⁻¹
- 155 mL min⁻¹
My answer: _____ Reason: ____________________________________
2. At one instant, left ventricular pressure is greater than left atrial pressure but lower than aortic pressure. Which valve state is expected?
- Mitral open; aortic open
- Mitral closed; aortic closed
- Mitral open; aortic closed
- Mitral closed; aortic open
My answer: _____ Reason: ____________________________________
3. Which chamber is X in this route?
- Lung capillaries
- Pulmonary veins
- X
- Left ventricle
- Right atrium
- Left ventricle
- Left atrium
- Right ventricle
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. Ventricular pressure falls below pressure in the aorta and pulmonary artery, reversing the pressure gradient and filling the valve pockets.
2. The capillary network has an enormous total cross-sectional area, so flow is distributed across many parallel vessels.
3. Yes, during isovolumetric contraction.
4. Semilunar valve closure after the pressure difference reverses.
5. No. They have different resistances and pressure requirements.
Applied questions
1. A — Cardiac output = heart rate × stroke volume = 75 × 80 = 6,000 mL min⁻¹, or 6 L min⁻¹.
2. B — Ventricular pressure above atrial pressure closes the mitral valve. Aortic pressure above ventricular pressure keeps the aortic valve closed. Both can be closed during isovolumetric phases.
3. C — Oxygenated blood returning from the lungs enters the left atrium through pulmonary veins, then passes to the left ventricle.