8 Questions
What is the main function of the SA node in the cardiac conduction system?
To set the pace of cardiac contraction
During which phase of the cardiac cycle does the heart pump blood?
Systolic phase
What percentage of blood flows passively from the atria to the ventricles during atrial diastole?
80%
What is the term for the volume of blood in the ventricles at the end of atrial systole?
End diastolic volume
During which phase of the cardiac cycle do the AV valves close?
Early ventricular systole
What is the duration of the atrial diastole phase?
0.7 seconds
What is the term for the first heart sound, created when the AV valves close?
S1
What is the duration of the systolic phase of the cardiac cycle?
300ms
Study Notes
Cardiac Cycle
- The cardiac cycle is a sequence of alternating contraction and relaxation of the atria and ventricles with every heartbeat.
- The systolic phase lasts for approximately 300ms, during which the heart chambers contract and pump blood.
- The diastolic phase lasts for approximately 500ms, during which the heart chambers relax and fill with blood.
Conduction System
- The SA node is a specialized area of cells located near the opening of the superior vena cava.
- The SA node is able to contract faster than the rest of the heart tissue and sets the pace of cardiac contraction.
- It is known as the pacemaker of the heart, and the impulse is spread to the rest of the heart through conductive pathways.
Phases of Cardiac Cycle
- Atrial diastole: blood fills the right and left atrium, causing atrial pressure to rise above ventricular pressure.
- Atrial systole (mid to late ventricular diastole): the SA node fires, causing atrial contraction, and the remaining 20% of blood flows to the ventricles.
- Early ventricular systole (isovolumetric contraction): depolarization is passed down to the ventricles, causing ventricular contraction and pressure to rise above atrial pressure.
- AV valves close to prevent backflow of blood, creating the S1 or lub sound (1st heart sound).
- Mid to late ventricular systole (ventricular ejection): not specified.
- Early ventricular diastole (isovolumetric relaxation): not specified.
Atrial Diastole
- Lasts for approximately 0.7 seconds.
- AV valves open, allowing 80% of blood to passively flow to the ventricles due to gravity.
Understand the sequence of cardiac cycle, including systolic and diastolic phases, and the conduction system of the heart. Learn how the heart chambers contract and relax, and how blood is pumped and filled.
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