Question

atrial systole begins ____________.

Explanation:

Atrial systole (contraction of the atria) begins after the end of ventricular diastole (relaxation of the ventricles) and is triggered by the electrical impulse from the sinoatrial (SA) node, typically following the filling of the atria with blood and just before ventricular systole. In the cardiac cycle, atrial systole starts when the atria contract to push remaining blood into the ventricles, occurring after the atria have passively filled during ventricular diastole and when the electrical signal from the SA node spreads to the atrial muscle cells. A common and precise answer to "Atrial systole begins ______" is "after ventricular diastole (or when the atria are electrically stimulated by the SA node to contract, typically to complete ventricular filling before ventricular systole)". The most standard physiological answer is that atrial systole begins to complete the filling of the ventricles, occurring after the atria have passively filled during ventricular diastole, and is initiated by the SA node's electrical impulse, so a concise fill - in is "to complete ventricular filling (or after ventricular diastole, or when the SA node triggers atrial contraction)". The key physiological point is that atrial systole starts to push the last bit of blood into the ventricles, happening after the atria have filled (during ventricular diastole) and when the SA node causes atrial muscle to contract. So the answer is that atrial systole begins to complete the filling of the ventricles (or more precisely, atrial systole begins when the atria contract to eject blood into the ventricles, which occurs after the atria have passively filled during ventricular diastole and is initiated by the sinoatrial node's electrical activity). A very specific and correct answer for the blank is "to complete ventricular filling (or after ventricular diastole, as part of the cardiac cycle to push blood into the ventricles)". The most accurate fill - in based on cardiac physiology is that atrial systole begins "to complete the filling of the ventricles" (or "after ventricular diastole" or "when the sinoatrial node initiates atrial contraction").

Answer:

after ventricular diastole (or to complete ventricular filling, or when the SA node triggers atrial contraction)