Coordinate contraction and valve action in a cardiac cycle
Use pressure differences to explain filling, ejection and prevented backflow.
Section B9.2 · Heart
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall atrioventricular and semilunar positions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What drives the valve flaps open and closed?
What you will learn
- Atrial contraction helps complete ventricular filling
- Ventricular pressure closes one route and opens another
Atrial contraction helps complete ventricular filling
During filling, the atrioventricular valves are open when atrial pressure exceeds ventricular pressure. Atrial contraction helps push blood into the ventricles. The semilunar valves remain closed when arterial pressure exceeds ventricular pressure, preventing backflow from the arteries.
The two atria act together and the two ventricles act together in the simplified normal cycle. It is not a sequence in which right atrium, right ventricle, left atrium and left ventricle each wait for a separate turn. The relaxation and filling stages also matter.
Ventricular pressure closes one route and opens another
As ventricles contract, pressure rises above atrial pressure and closes the atrioventricular valves. When ventricular pressure exceeds arterial pressure, the semilunar valves open and blood is ejected into the arteries. Valve movements are driven by pressure differences; valves do not contract as separate pumps.
When ventricles relax, their pressure falls. Arterial pressure then closes the semilunar valves; once atrial pressure exceeds ventricular pressure, atrioventricular valves reopen for filling. The supplied three-stage model focuses on filling, ejection and relaxation, and does not imply an instantaneous switch with no brief closed-valve intervals.
Sources for this lesson
Pause and explain
Which state describes ventricular ejection?
Worked example
Predict valve action during ventricular ejection after ventricular pressure exceeds both atrial and arterial pressure.
Show the worked solution
- Higher ventricular pressure closes the atrioventricular route back to atria.
- Higher ventricular pressure opens the semilunar route into arteries.
Answer Atrioventricular closed; semilunar open; blood is ejected into arteries.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State valve conditions during ventricular filling when atrial pressure exceeds ventricular pressure and arterial pressure exceeds ventricular pressure.
Give me a hint
Apply each pressure difference separately.
Compare my reasoning
- Atrium-to-ventricle pressure opens atrioventricular valves.
- Artery-to-ventricle pressure closes semilunar valves.
Atrioventricular open; semilunar closed.
Look for these in your work
- Compare atrial and ventricular pressure
- Compare arterial and ventricular pressure
Describe the sequence from ventricular contraction to ejection.
Give me a hint
The exit opens only once pressure is sufficient.
Compare my reasoning
- Ventricular pressure rises and closes atrioventricular valves.
- When it exceeds arterial pressure, semilunar valves open and blood leaves.
Contraction raises ventricular pressure, closes atrioventricular valves and then opens semilunar valves when arterial pressure is exceeded.
Look for these in your work
- Prevent atrial backflow
- Link semilunar opening with arterial comparison
During relaxation ventricular pressure falls below arterial pressure. Predict the exit valve and then explain how filling can resume.
Give me a hint
Use artery-to-ventricle and then atrium-to-ventricle differences.
Compare my reasoning
- Semilunar closes to prevent arterial backflow.
- Atrioventricular opens once atrial pressure exceeds ventricular pressure.
Semilunar valves close; atrioventricular valves reopen when the atrial-to-ventricular pressure difference favours filling.
Look for these in your work
- Explain exit closure
- Explain renewed filling condition
Common mistakes
- Claiming all valves stay open throughout contraction.
- Calling valves active muscular pumps.
What can you explain now?
Which state describes ventricular ejection?
Compare with the explanation
Atrioventricular closed; semilunar open
Blood leaves ventricles into arteries while atrial backflow is prevented.
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Make it stick
Describe filling, ejection and relaxation using both valve categories and pressure comparisons.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.