IB Biology Topic B3.2.16: Stages in the Cardiac Cycle Notes

The Cardiac Cycle: One Heartbeat, Three Coordinated Stages

The cardiac cycle is the sequence of events in one heartbeat that keeps blood moving in one direction.

It has three stages, each driven by changing pressures that open and close the valves:

Atrial systole: the atria contract, pushing blood into the ventricles.
Ventricular systole: the ventricles contract, ejecting blood into the arteries.
Diastole: the heart relaxes and refills with blood.

Note

The sinoatrial node (SA node) is the heart's pacemaker.
It fires the electrical impulses that set the timing of each cardiac cycle.

Stage 1: Atrial Systole Tops Up the Ventricles

The SA node fires, triggering the atria to contract.

Atrial pressure rises, forcing blood through the open AV valves into the relaxed ventricles.

The semilunar valves stay closed, so blood cannot yet leave for the arteries.

This stage lasts about 0.1 seconds and tops the ventricles up to full volume.

Analogy

Picture the atrium as a hand giving a nearly full water balloon one last squeeze.
That final push tops up the ventricle before it contracts.

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IB Biology Topic B3.2.16: Stages in the Cardiac Cycle Notes

The Cardiac Cycle: One Heartbeat, Three Coordinated Stages

Stage 1: Atrial Systole Tops Up the Ventricles

Stage 2: Ventricular Systole Ejects Blood Into the Arteries

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

The Cardiac Cycle: One Heartbeat, Three Coordinated Stages

Stage 1: Atrial Systole Tops Up the Ventricles

Stage 2: Ventricular Systole Ejects Blood Into the Arteries

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic B3.2.16: Stages in the Cardiac Cycle Notes

The Cardiac Cycle: One Heartbeat, Three Coordinated Stages

Stage 1: Atrial Systole Tops Up the Ventricles

Stage 2: Ventricular Systole Ejects Blood Into the Arteries

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

The Cardiac Cycle: One Heartbeat, Three Coordinated Stages

Stage 1: Atrial Systole Tops Up the Ventricles

Stage 2: Ventricular Systole Ejects Blood Into the Arteries

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics