1.3 Cardiac cycle

Cardiac Cycle

The sequence of events in the heart during one heartbeat, including contraction and relaxation phases.

Diastole

The phase of the cardiac cycle when the heart muscle relaxes and chambers fill with blood.

Systole

The phase of the cardiac cycle when the heart muscle contracts and pumps blood out of the chambers.

Mid-to-late diastole

The phase of the cardiac cycle where the heart is filling with blood; involves passive filling and atrial contraction.

Ventricular systole

The phase of the cardiac cycle where the ventricles contract, forcing blood into the aorta and pulmonary arteries.

Early diastole

The phase where the ventricles relax and blood flows into the heart from the atria.

Isovolumetric contraction phase

The stage of ventricular systole when the ventricles contract with no volume change because all valves are closed.

End Diastolic Volume (EDV)

The total volume of blood in the ventricles at the end of diastole before contraction.

End Systolic Volume (ESV)

The volume of blood remaining in a ventricle after contraction.

Cardiac Output (CO)

The volume of blood the heart pumps per minute, calculated as heart rate multiplied by stroke volume.

Stroke Volume (SV)

The volume of blood pumped from the ventricle with each heartbeat.

Frank-Starling law of the heart

States that the more the heart fills with blood during diastole, the more it contracts during systole.

Contractility

The strength of the heart's contraction, affecting the volume of blood ejected during systole.

Afterload

The resistance the heart must work against to eject blood during systole.

Cardioacceleratory center

Part of the autonomic nervous system that increases heart rate.

Cardioinhibitory center

Part of the autonomic nervous system that decreases heart rate.

Hormonal regulation of heart rate

Influence of hormones like epinephrine and thyroxine on the heart's activity.

Dicrotic notch

A small dip in arterial pressure that occurs when the semilunar valves close.

Heart sounds

Sounds produced by the closing of the heart valves, commonly referred to as 'Lub' and 'Dub' during the cardiac cycle.