Control and Regulation of Cardiac Cycle

The Cardiac Cycle

The cardiac cycle refers to a complete heartbeat that includes diastole, systole, and the intervening pause.

Diastole: The period during which the heart relaxes and the chambers fill with blood.
Systole: The period where the heart contracts, leading to the ejection of blood into the circulatory system.
Pause: A brief moment of rest that occurs after systole and before another diastole phase.

Control and Regulation of the Cardiac Cycle

The cardiac cycle is regulated by two types of controls: intrinsic (coming from within the heart) and extrinsic (coming from outside the heart).

Intrinsic Control

The heart has a natural pacemaker named the sinoatrial node (SA node), located in the right atrium. It initiates each heartbeat and determines heart rate.
Electrical impulses generated by the SA node spread across the atria, causing them to contract.
The signal is then passed to the atrioventricular node (AV node), which acts as an electrical bridge allowing signals to travel from the atria to the ventricles.
This careful sequence ensures the right timing for blood flow – atria contract first to push blood into the ventricles, followed by the ventricles contracting to push blood out of the heart.

Extrinsic Control

The cardiac cycle is also controlled by extrinsic factors, through the autonomic nervous system (ANS), which includes the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system speeds up heart rate and increases the force of contraction, preparing the body for ‘fight or flight.’
The parasympathetic nervous system, through the vagus nerve, slows down the heart rate, allowing the body to be in a ‘rest and digest’ state.

Understanding the Balance

A fine balance between the sympathetic and parasympathetic systems, guided by the needs of the body, maintains the heart’s normal rhythm and force of contraction. Changes in this balance can result in cardiac disorders including tachycardia (rapid heart rate) and bradycardia (slow heart rate).

It is crucial to understand the control and regulation of the cardiac cycle to comprehend these cardiac disorders and their impact on individuals, forming a fundamental part of knowledge within Health and Social Care.