Electrocardiogram (ECG) (cont.)

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Picture of the basic anatomy of the heart

The heart has four chambers – the right and left atrium and the right and left ventricle.

The right side of the heart collects blood from the body and pumps it to the lungs while the left side of the heart receives blood from the lungs and pumps it to the body.

Blood flows through the body in the following way:

• Oxygen-rich blood from the lungs enters the left atrium through the pulmonary veins.
• Blood then flows into the left ventricle where it is pumped into the aorta and is distributed to the rest of the body. This blood supplies organs and cells with oxygen and nutrients necessary for metabolism.
• Blood that returns to the heart is depleted of oxygen and carries carbon dioxide, the waste product of metabolism. The blood enters the right atrium though the vena cava, where it is collected and pumped to the right ventricle.
• The right ventricle then pumps blood through the pulmonary artery to the lungs where carbon dioxide is stripped off, oxygen is replaced, and the cycle begins again.

Picture of heart anatomy blood flow

Like any muscle, the heart requires oxygen and nutrients to function. Oxygen and nutrients are supplied by arteries that originate from the aorta. These vessels branch out to supply all the regions of the heart with oxygen rich blood.

Electrically, the heart can be divided into upper and lower chambers. An electrical impulse is generated in the upper chambers of the heart that causes the atria to squeeze and push blood into the ventricles. There is a short delay to allow the ventricles to fill. The ventricles then contract to pump blood to the body and the lungs.

Conducting system of the heart: SA means sinoatrial node. AV means atrioventricular node. RB and LB mean right and left bundle, respectively, and are the nerves that spread the electric impulse from the AV node into the ventricles.

The heart has its own automatic pacemaker called the sinaoatrial, or SA node, located in the right atrium. The SA node acts independently of the brain to generate electricity for the heart to beat.

• Normally, the impulse generated by the SA node runs through the heart's electrical grid and signals the muscle cells in the atria to beat simultaneously, allowing for a coordinated squeeze of the heart. Contraction of the atria pushes blood into the ventricles.
• The electrical signal that was generated in the SA node travels to a junction box between the atria and ventricles (the AV node) where it is delayed for a few milliseconds to allow the ventricles to fill.
• The electrical signal then travels through the ventricles, stimulating those heart muscle cells to contract. Ventricular contraction pumps blood to the body (from the left ventricle) and the lungs (from the right ventricle).
• There is a short pause to allow blood to return to the heart and fill before the electrical cycle repeats itself for the next heartbeat.

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