Anatomy of the heart

Location of the Heart
  • Structure: The heart is a hollow muscular organ.
  • Location:
    • The heart lies in the mediastinum, the space between the lungs, in the chest.
    • Approximately two-thirds of the heart is located to the left of the midline of the sternum.
Size and Shape of the Heart
  • The adult heart dimensions are approximately:
    • Length: Roughly 5 inches5\text{ inches} (12 cm12\text{ cm})
    • Width: Roughly 3.5 inches3.5\text{ inches} (9 cm9\text{ cm})
    • Thickness: Roughly 2.5 inches2.5\text{ inches} (6 cm6\text{ cm})
  • The size is roughly equivalent to the owner’s fist.
Surfaces of the Heart
  • Base:
    • Posterior surface including the left atrium, small portion of the right atrium, proximal portions of the superior and inferior venae cavae, and the pulmonary veins.
  • Anterior Surface:
    • Lies behind the sternum and costal cartilages, primarily the right ventricle.
  • Apex:
    • Lower portion of the heart formed by the tip of the left ventricle.
    • It points downward, forward, and to the left, typically located at the level of the fifth intercostal space.
Heart Coverings and Wall Layers
  1. Pericardium: A double-walled sac that encloses the heart.
    • Fibrous Pericardium: The outer tough, connective tissue layer that prevents over-distention.
    • Serous Pericardium: Consists of the parietal layer (lining the fibrous pericardium) and the visceral layer (also known as the epicardium).
  2. Cardiac Muscle Layers:
    • Epicardium: The outermost layer, also known as the visceral pericardium.
    • Myocardium: The middle, thickest layer composed of cardiac muscle cells responsible for contraction.
    • Endocardium: The innermost layer of smooth endothelial tissue that lines the chambers and covers the heart valves.
Chambers and Vessels
  1. Atria: The two superior receiving chambers.
    • Right Atrium: Receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus.
    • Left Atrium: Receives oxygenated blood from the four pulmonary veins.
  2. Ventricles: The two inferior pumping chambers.
    • Right Ventricle: Pumps blood into the pulmonary trunk toward the lungs.
    • Left Ventricle: The thickest chamber; pumps blood into the aorta to the systemic circulation.
Heart Valves
  • Atrioventricular (AV) Valves: Located between the atria and ventricles. Includes the Tricuspid valve (right) and the Mitral/Bicuspid valve (left).
  • Semilunar Valves: Located at the exits of the ventricles. Includes the Pulmonary valve and the Aortic valve.
Cardiac Dynamics
  • Atrial Kick: The additional volume of blood (approximately 20% to 30%20\%\text{ to }30\%, contributed to the ventricles by atrial contraction just before the ventricles contract.
  • Blood Flow Sequence: Right atrium $\rightarrow$ Tricuspid valve $\rightarrow$ Right ventricle $\rightarrow$ Pulmonary valve $\rightarrow$ Pulmonary arteries $\rightarrow$ Lungs $\rightarrow$ Pulmonary veins $\rightarrow$ Left atrium $\rightarrow$ Mitral valve $\rightarrow$ Left ventricle $\rightarrow$ Aortic valve $\rightarrow$ Aorta.