Cardiovascular System: Heart, Arteries, and Veins

• The components of the cardiovascular system: heart, artery/arteriole, vein/venule, and capillary.
• The primary organ of the cardiovascular system is the heart, which is a muscle made up of three layers.

Heart Layers

• Endocardium is the thin inner layer
• Myocardium is the muscular middle layer
• Epicardium is the outer protective layer.

Coronary Circulatory Network

• Includes the right coronary artery, left coronary artery, collateral circulation and coronary veins
• There are four inner chambers in the heart
• The right and left atria are the top chambers
• The right and left ventricles are the bottom chambers.
• The right atria receives deoxygenated blood from the superior and inferior vena cava
• The left atria receives oxygenated blood from the pulmonary veins
• The structures of the cardiovascular system work together to pump blood throughout the body
• The average adult heart beats 60 to 100 times per minute at rest

Pulmonary and systemic circuits

• Pulmonary arteries carry blood in the pulmonary circuit
• Pulmonary veins bring blood back from the gas exchange
• Deoxygenated blood returns from systemic circulation via the superior vena cava (SVC) and inferior vena cava (IVC) to the right atria
• Blood empties to the right ventricle via the tricuspid valve and gets ejected into the pulmonary artery
• Oxygenated blood flows from the pulmonary veins back to the left atria after oxygen-carbon dioxide exchange
• Blood ejects through the mitral valve into the left ventricle
• Blood is ejected through the aortic valve into the aorta upon ventricle contraction

Cardiac Output

• Ejection fraction is the percent of end diastolic volume ejected with each heartbeat in the left ventricle
• Cardiac output (CO) signifies the amount of blood pumped by the ventricle per minute, measured in liters
• The formula for calculating cardiac output is CO = SV × HR
• Stroke volume (SV) is the amount of blood ejected with each heartbeat

Factors influencing stroke volume:

• Preload is the degree of stretch of cardiac muscle fibers at the end of diastole
• Afterload is the resistance encountered when blood is ejected from the ventricle
• Contractility refers to the cardiac muscle's ability to shorten in response to an electrical impulse

Factors influencing heart rate

• Autonomic nervous system and baroreceptors

Factors influencing stroke volume:

• Preload: Frank-Starling Law
• Afterload: affected by systemic vascular resistance and pulmonary vascular resistance

Preload Definition

• Volume of blood in ventricles at the end of diastole (which is end diastolic pressure) and increases in states of:
• Hypervolemia
• Regurgitation of cardiac valves
• Heart Failure

Afterload Definition

• Resistance left ventricle must overcome to circulate blood and Increases in states of:

  • Hypertension
  • Vasoconstriction

• Increase in Afterload = Increase in Cardiac Workload

Electrical Conduction

• Sinoatrial node
• Internodal pathways
• AV junction
• Bundle branches
• Final action is repolarization

Depolarization vs. Repolarization

• Depolarization (Contraction) is when cells transmit the electrical impulse down the conduction system to stimulate muscle contraction
• Repolarization (Relaxation) occurs in the opposite direction, where the last cells to depolarize are the first to repolarize, involing chemical pumps reversing the internal negative charge to a resting state