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Interpreting the Graph on Pressure Changes in the Heart


The topic on Transport in Humans is a long one and by the time we reach the sub-topic of the heart, some students find it a tad tough to follow... one of the more complicated concepts that students take a bit longer to grasp is the one on pressure changes in the heart. And so, I thought I should dedicate one blog post on this.


This graph is not frequently tested, a flip through the pure Biology TYS showed that it appeared four times in the past 10 years: three in Paper 1 and once in Paper 2. Usually, the question is testing your knowledge on the closing/opening of the valves in the heart at different points in one cardiac cycle. Sometimes, the deduction of the length of a phase in the cardiac cycle (e.g. ventricular systole) is also tested.


Most of my explanations have been annotated in the diagrams below, I think it's easier to understand with direct reference to the different parts of the graph.


I've split them up into 3 different parts:

  • atrial systole (when muscles of atrium relax)

  • ventricular systole (when muscles of ventricle contract)

  • ventricular diastole and atrial diastole (when muscles of both atrium and ventricle relax)

Photo credit: The graph I used in all the diagrams below is taken from O level Biology Paper Nov 2013 5094/02/1(c).


Atrial Systole

The gif above shows the section of the graph where Atrial Systole takes place (between 0 to 0.1 sec).


The figure above shows an annotated diagram of significant events occurring during Atrial Systole.


Ventricular Systole

The gif above shows the section of the graph where Ventricular Systole takes place (between 0.1 to 0.4 sec).


The figure above shows an annotated diagram of significant events occurring during Ventricular Systole.


Ventricular Diastole & Atrial Systole

The gif above shows the section of the graph where ventricular diastole and atrial diastole both take place (between 0.4 to 0.8 sec).


The figure above shows an annotated diagram of significant events occurring during ventricular diastole and atrial diastole.


I hope the annotations were easy to understand... Let me know if you have any questions or feedback. Just drop me a message!


Till the next post, stay safe!


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