Introduction to the Cardiovascular System

• The heart keeps the blood in motion, preventing nutrient and oxygen depletion and waste accumulation.

• The heart beats approximately 100,000 times per day (about 70 beats per minute) and pumps roughly 1.5 million gallons of blood annually (about 2.9 gallons per minute).

• The volume of blood pumped varies from 5 to 30 liters per minute.

Overview of the Cardiovascular System

• The heart, about the size of a clenched fist, contains four chambers:

  • Two atria (upper chambers)

  • Two ventricles (lower chambers)

• The heart functions in two circuits:

  • Pulmonary circuit (to and from the lungs)

  • Systemic circuit (to and from the rest of the body)

Chambers of the Heart

• Right Atrium: Receives oxygen-poor blood via superior and inferior vena cava and coronary sinus. Contains pectinate muscles and fossa ovalis.

• Right Ventricle: Receives blood from the right atrium through the tricuspid (AV) valve, sends blood to the pulmonary trunk via the pulmonary valve.

• Left Atrium: Receives oxygenated blood from lungs via pulmonary veins, sends blood to left ventricle through the mitral (bicuspid) valve.

• Left Ventricle: Thicker walls for systemic pumping; sends blood through the aortic valve into the aorta.

Structure of the Heart

• The heart comprises three layers of tissue:

  • Epicardium: External surface, also called visceral pericardium.

  • Myocardium: Thick muscular layer composed of cardiac muscle tissue; promotes contraction.

  • Endocardium: Inner lining made up of endothelial tissue.

• Intercalated Discs: These specialized junctions between cardiac cells support synchronized contractions by allowing ion movement (gap junctions) and binding cells together (desmosomes).

Heart Valves and Function

• Four major valves:

  • Atrioventricular (AV) valves: Tricuspid (right) and bicuspid (mitral, left) valves prevent backflow during ventricular contraction.

  • Semilunar valves: Aortic and pulmonary valves open upon ventricular contraction to allow blood ejection.

• Chordae tendineae and papillary muscles stabilize AV valves during contraction to prevent inversion.

Conducting System and Cardiac Cycle

• The heart's conduction system coordinates contractions:

  • Sinoatrial (SA) Node: Primary pacemaker, generates 80-100 action potentials per minute.

  • Atrioventricular (AV) Node: Delays impulses allowing atria to contract before ventricles.

  • Bundle Branches and Purkinje Fibers: These fibers facilitate rapid impulse conduction throughout the ventricles, ensuring efficient contraction.

Autonomic Control of Heart Rate

• Heart rate is modifiable by the autonomic nervous system:

  • Sympathetic Stimulation: Norepinephrine increases heart rate and contraction strength.

  • Parasympathetic Stimulation: Acetylcholine decreases heart rate and contraction strength.

• Cardiac centers in the medulla oblongata regulate heart activity.

Summary of Key Concepts

• The heart consists of chambers, valves, and specialized conduction pathways.

• It functions in a rhythmic cycle, pumping blood throughout the body and is influenced by the autonomic nervous system.