2.7.11Inquiry Process
The Cardiac Cycle- Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 83 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Phases of the Cycle
Valves open and close purely in response to pressure differences.
1
Atrial systole: the atria contract, pushing the last blood into the ventricles while the atrioventricular valves are open.
2
Ventricular systole begins: ventricular pressure rises above atrial pressure, so the atrioventricular valves slam shut, producing the first heart sound.
3
When ventricular pressure exceeds pressure in the aorta and pulmonary artery, the semilunar valves open and blood is ejected.
4
Diastole: the ventricles relax, pressure falls below arterial pressure, and the semilunar valves close, producing the second heart sound.
5
When ventricular pressure drops below atrial pressure, the atrioventricular valves open again and blood flows passively into the ventricles.
Section 2 of 5Reading Pressure Graphs
Atrial pressure
- Atrial pressure Remains low throughout, with small rises when the atria contract and when they fill during ventricular systole.
Ventricular pressure
- Ventricular pressure Rises sharply during ventricular systole and falls during diastole;
- the left ventricle reaches a much higher peak than the right.
Aortic pressure
- Aortic pressure Rises when blood is ejected and stays high while the elastic aorta recoils;
- a small dip marks closure of the semilunar valve.
Crossover points
- Crossover points The points at which one pressure line crosses another mark the opening and closing of valves.
| Valve | Opens when | Closes when |
|---|---|---|
| Atrioventricular | Atrial pressure exceeds ventricular | Ventricular pressure exceeds atrial |
| Semilunar | Ventricular pressure exceeds arterial | Arterial pressure exceeds ventricular |
Section 3 of 5Rate and Output
Rate and Output
Cycle length
- Cycle length Duration of one cycle in seconds equals 60 divided by the heart rate in beats per minute.
Stroke volume
- Stroke volume The volume of blood pumped by one ventricle in a single contraction.
Cardiac output
- Cardiac output Cardiac output equals heart rate multiplied by stroke volume, measured in volume per minute.
Exercise
- Exercise Both heart rate and stroke volume increase, so cardiac output can rise several times above resting levels.
Section 4 of 5Worked Example
Question
- A resting heart beats at 75 beats per minute with a stroke volume of 70 cm³.
- Calculate the length of one cycle and the cardiac output in dm³ per minute.
- Cycle length = 60 ÷ 75 = 0.8 s.
- Cardiac output = 75 × 70 = 5250 cm³ per minute.
- Convert5250 cm³ ÷ 1000 = 5.25 dm³ per minute.
Answer One cycle lasts 0.8 s and cardiac output is 5.25 dm³ per minute.
Section 5 of 5Exam Checklist & Tips
2.7.11 – Key Points for the Exam
- Systole The phase of the cardiac cycle in which heart muscle contracts.
- Diastole The phase in which heart muscle relaxes and the chambers fill.
- Stroke volume Volume of blood ejected from a ventricle per beat.
- Cardiac output Volume of blood pumped by a ventricle per minute.
Common Mistakes
- Believing valves are controlled by nerves; they respond to pressure differences.
- Saying that heart sounds are caused by the muscle contracting; they are caused by valves closing.
- Confusing systole with diastole when reading graphs.
- Calculating cardiac output without matching units, such as mixing cm³ and dm³.
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