فسيولوجيا القلب - النظام الكهربائي

Physiology of the Cardiovascular System

• The heart has four chambers: two atria and two ventricles.
• The right atrium receives deoxygenated blood from the body and pumps it into the right ventricle.
• The right ventricle pumps the blood to the lungs for oxygenation.
• Oxygenated blood then flows to the left atrium.
• The left atrium pumps the blood into the left ventricle.
• The left ventricle pumps the oxygenated blood to the rest of the body.

Cardiac Cycle: Systole

• Systole is the period of ventricular contraction and ejection.
• End-systolic volume (ESV) is the volume of blood remaining in the ventricles at the end of systole.
• ESV represents the lowest volume of blood in the ventricles during the cardiac cycle.

Cardiac Cycle: Diastole

• Diastole is the period of ventricular relaxation and filling.
• End-diastolic volume (EDV) is the volume of blood in the ventricles at the end of diastole, just before contraction.
• EDV is the maximum volume of blood in the ventricles during the cardiac cycle.

Sinoatrial (SA) Node

• The SA node, also known as the sinoatrial node, is a group of specialized muscle cells located in the right atrium.
• The SA node initiates the heartbeat by generating electrical impulses that trigger the contraction of the atria and ventricles.
• The SA node has an inherent pacemaker activity, generating electrical impulses at a rate of approximately 72 times per minute.

Atrioventricular (AV) Node

• The AV node is a specialized group of cells located in the lower part of the right atrium.
• It transmits electrical impulses from the SA node to the ventricles, ensuring a coordinated contraction.

Electrocardiogram (ECG)

• An ECG is a recording of the electrical activity of the heart over time.
• The ECG measures the electrical potentials generated by the heart's conduction system, reflecting the different phases of the cardiac cycle.
• The key elements on an ECG include P-wave, QRS complex, and T-wave, reflecting atrial depolarization, ventricular depolarization, and ventricular repolarization, respectively.

Factors affecting blood flow

• Blood flow is directly proportional to pressure difference (ΔP) and inversely proportional to resistance (R).
• Blood flow also is directly proportional to the fourth power of the radius (r4) of the blood vessel. This means the flow is greatly affected by a very small change in the radius.
• Blood flow is inversely proportional to the length (L) of the vessel and viscosity (η) of the blood.

Cardiac Output and Heart Rate

• Cardiac output is the volume of blood pumped by the heart per minute.
• Heart rate is the number of heartbeats per minute.