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1.2.3Unit 1: Lifestyle, Transport, Genes and Health

The Cardiac Cycle — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 15 of 29 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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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.
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Part 1 of 5Structure of the Heart

Chambers
  • Chambers The heart has two thin-walled atria that receive blood and two thick-walled ventricles that pump it out.
Septum
  • Septum A muscular wall separates the left and right sides so that oxygenated and deoxygenated blood do not mix.
Atrioventricular valves
  • Atrioventricular valves The tricuspid valve on the right and the bicuspid valve on the left stop blood flowing back into the atria.
Semilunar valves
  • Semilunar valves The pulmonary valve and the aortic valve stop blood returning from the arteries to the ventricles.
Ventricle walls
  • Ventricle walls The left ventricle wall is thicker than the right because it must pump blood around the whole body rather than just to the nearby lungs.

Part 2 of 5The Three Stages

1
Atrial systole: the atria contract, increasing the pressure and pushing the remaining blood through the open atrioventricular valves into the ventricles.
2
Ventricular systole: the ventricles contract, pressure rises above that in the atria, the atrioventricular valves slam shut and the semilunar valves open as blood is forced into the arteries.
3
Diastole: the heart muscle relaxes, pressure falls, the semilunar valves close, and blood from the veins flows into the atria and on into the ventricles.
4
The closing of the valves produces the heart sounds heard through a stethoscope.
5
The cycle then repeats continuously, and a resting heart typically completes it in less than a second.

Part 3 of 5Valves and Pressure

Valves and Pressure
Opening rule
  • Opening rule A valve opens when the pressure behind it is higher than the pressure in front of it, so blood flows forwards.
Closing rule
  • Closing rule A valve closes when the pressure in front of it is higher than behind, which prevents any backflow.
Tendons
  • Tendons Tendinous cords attach the atrioventricular valves to the ventricle wall and stop the valves from turning inside out.
Coronary arteries
  • Coronary arteries These supply the heart muscle itself with oxygenated blood;
    • a blockage can lead to a heart attack.

Part 4 of 5Worked Example

Question

  • One cardiac cycle of a resting heart lasts 0.8 seconds.
  • Calculate the heart rate in beats per minute.

  1. Heart rate = 60 seconds ÷ time for one cycle in seconds.
  2. Heart rate = 60 ÷ 0.8.
  3. Heart rate = 75.

Answer The heart rate is 75 beats per minute.

Part 5 of 5Exam Checklist & Tips

1.2.3 – Key Points for the Exam

  • Systole The contraction phase of the cardiac cycle.
  • Diastole The relaxation phase of the cardiac cycle.
  • Atrioventricular valve A valve between an atrium and a ventricle.
  • Semilunar valve A valve between a ventricle and an artery.

Common Mistakes

  • Saying that blood flows from the atria to the ventricles because the atria contract only;
    • the ventricles also fill passively during diastole.
  • Stating that the atrioventricular valves open when ventricular pressure is higher than atrial pressure;
    • they close.
  • Mixing up the tricuspid (right) and bicuspid (left) valves.
  • Believing that the left ventricle is thicker because it holds more blood;
    • it is thicker because it generates higher pressure.

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