Lecture Notes: Key Concepts of the Heart

Overview of Heart Anatomy

• Chambers:
  • Four chambers: two atria (left and right) and two ventricles (left and right).
• Blood Vessels:
  • Right atrium receives blood from the superior and inferior vena cava and coronary circulation.
  • Blood exits the right ventricle via the pulmonary trunk (splits into left and right pulmonary arteries).
  • Left side vessels (pulmonary veins) carry oxygen-rich blood to the left atrium.
  • Aorta receives blood from left ventricle, supplying systemic circulation.

Heart Valves

• Atrioventricular (AV) Valves:
  • Right AV valve: tricuspid valve.
  • Left AV valve: bicuspid or mitral valve.
• Semilunar Valves:
  • Pulmonary semilunar valve and aortic semilunar valve.

Path of Blood Through the Heart

1. Start at right atrium.
2. Through tricuspid valve to right ventricle.
3. To pulmonary semilunar valve, pulmonary trunk, pulmonary arteries, lungs.
4. Oxygenated blood returns via pulmonary veins to left atrium.
5. Through mitral valve to left ventricle.
6. Through aortic semilunar valve to aorta, then systemic circulation.
7. Blood returns deoxygenated to right atrium via vena cavae.

Cardiac Output

• Formula: Cardiac Output = Heart Rate x Stroke Volume
• Heart Rate: Beats per minute, influenced by chronotropic agents (positive increases, negative decreases).
• Stroke Volume: Volume of blood per ventricle, influenced by:
  • Preload: Degree of stretch in heart muscles (increased preload increases stroke volume).
  • Contractility: Strength of contraction (positive inotropic agents increase contractility).
  • Afterload: Pressure ventricles must overcome to eject blood (increased afterload reduces stroke volume).

Cardiac Cycle

• Phases:
  • Ventricular Filling: Passive then atrial systole (blood fills ventricles).
  • Isovolumetric Contraction: Ventricles contract with closed AV valves (pressure increase without volume change).
  • Ejection Phase: Semilunar valves open, blood ejected from ventricles.
  • Isovolumetric Relaxation: Ventricles relax, semilunar valves close (prepares for next cycle).
• Heart Sounds:
  • "Lub": AV valves closing.
  • "Dub": Semilunar valves closing.

EKG (Electrocardiogram)

• Measures: Electrical activity in the heart.
• Components:
  • P Wave: Atrial depolarization.
  • QRS Complex: Ventricular depolarization (and hidden atrial repolarization).
  • T Wave: Ventricular repolarization.
• Conduction System:
  • SA node, AV node, AV bundle, bundle branches, Purkinje fibers.

Additional Concepts

• Electrical activity drives mechanical actions (contraction/relaxation).
• Conduction system sets heart rhythm, impacts cardiac output.