THE CARDIAC CYCLE

Question 1

is the flow of blood through the heart coordinated by electrochemical signals that cause the heart muscle to contract and relax.

Answer 1

The cardiac cycle

Question 2

Two phases of cardiac cycle are called:

Answer 2

 Systole (contraction)
 Diastole (relaxation)

Question 3

Electrical Conduction: Step by Step
1. Signal initiation at the sinoatrial (SA) node

2. Atrial contraction
3. Delay at the atrioventricular (AV) node
4. Impulse transmission to ventricles

Question 4

Cardiac Cycle and Heart Sounds: Step by Step

 “Lub” (S1): This sound is heard at the start of ventricular systole, when the ventricles contract and pump out blood of the heart. The mitral and tricuspid valves close to prevent blood from flowing back into the atria.

 “Dub” (S2): This sound occurs at the end of ventricular systole, as the ventricles begin to relax and fill with blood (diastole). The aortic and pulmonary valves close, preventing blood from flowing back into the ventricles.

Physiological splitting of the S2 sound
This occurs because the pulmonary valve closes slightly after the aortic valve, leading to a brief separation of the “dub” sound into two distinct components.

Question 5

What Makes the Heart Pump?

The heart pumps blood because of special muscle cells called cardiac muscle cells or cardiomyocytes.

 Are striated (have stripes) distinctive cells like skeletal muscles.

 Pump involuntarily and rhythmically like smooth muscles.

 Are connected to each other by intercalated disks (found only in the heart).

Question 6

Why Are Intercalated Disks Important?

 These disks connect one heart cell to another.

 They help electrical signals pass quickly from one cell to the
next.

 This allows the heart to pump in a coordinated and strong way.

Question 7

How Do We See the Heart’s Activity?

 The heart’s electrical impulses create small electric currents.

 These currents travel through the body.

 We can detect them on the skin using electrodes.

 The recording made by these electrodes is called an ECG
(Electrocardiogram).

Question 8

What Is an ECG?

 An ECG is a graph of the heart’s electrical signals.

 It shows how the heart beats and functions.

 Doctors use it to check if the heart is healthy or has problems.