Interior Heart

Anatomy of the Heart

Overview of Cardiac Veins

  • The small cardiac vein collects blood that eventually drains into the right atrium.

  • Most cardiac veins empty into the coronary sinus, located in the coronary sulcus on the posterior side of the heart.

Internal Anatomy of the Heart

  • The internal structure includes four main chambers: right atrium, left atrium, right ventricle, and left ventricle.

Right Atrium

  • The right atrium receives blood via:

    • Coronary sinus: This structure collects blood from the heart muscle itself and empties into the right atrium.

    • Superior vena cava:

    • Function: Collects deoxygenated blood from the upper part of the body, which includes the head, neck, shoulders, and upper limbs.

    • Inferior vena cava:

    • Function: Drains deoxygenated blood from the lower part of the body.

  • The right atrium receives blood from:

    • Three veins: the two vena cavae and the coronary sinus.

Left Atrium

  • The left atrium receives

    • Oxygenated blood from the lungs.

  • Four veins bring blood to the left atrium, termed pulmonary veins:

    • Two left pulmonary veins.

    • Two right pulmonary veins.

Atrioventricular Valves (AV Valves)

  • Located between the atria and ventricles, allowing unidirectional blood flow from the atria to ventricles.

  • Types of AV valves:

    • Right atrioventricular valve (Tricuspid valve):

    • Allows deoxygenated blood flow from the right atrium to the right ventricle.

    • Left atrioventricular valve (Bicuspid valve / Mitral valve):

    • Allows oxygenated blood flow from the left atrium to the left ventricle.

  • Functioning of AV valves:

    • Open when pressure in atria is higher than in ventricles.

    • Close when ventricles contract, preventing backflow into the atria.

  • Challenges with AV Valves:

    • The ventricles have thicker muscles allowing for stronger contractions, which can push AV valve cusps backward if not managed.

Supporting Structures for AV Valves

  • Trabeculae carne:

    • Muscle ridges within the ventricles.

  • Papillary muscles:

    • Tall muscles connected to AV valves; they contract and help keep the valves closed by controlling the tension on the chordae tendineae.

  • Chordae tendineae:

    • Tendon-like structures that connect the papillary muscles to the cusps of the AV valves, preventing them from flapping backward during ventricular contraction.

Septa of the Heart

  • Interventricular septum:

    • Separates the right and left ventricles.

  • Interatrial septum:

    • Separates the right and left atria.

    • Contains fossa ovalis: an oval-shaped depression marking the spot where the foramen ovale, a fetal connection between atria, closed after birth.

Cardiac Muscle Structure

  • The heart wall comprises three layers:

    • Epicardium: Outermost layer.

    • Endocardium: Innermost layer lining the heart chambers.

    • Myocardium: Thick middle layer made primarily of cardiac muscle, thicker in ventricles than in atria.

  • The left ventricle has a thicker muscle wall compared to the right ventricle due to its need to pump blood throughout the entire body, whereas the right ventricle pumps blood only to the lungs.

Atrial Features

  • Pectinate muscles:

    • Muscle ridges visible in the anterior wall of the right atrium. They are less prominent in the left atrium, hidden within elevations termed auricles.

  • Auricles:

    • Balloon-shaped elevations present in both atria, where pectinate muscles reside in the left atrium.

Ventricular Pumping Action

  • Right Ventricle:

    • Contracts to pump deoxygenated blood into the pulmonary trunk via the pulmonary semilunar valve.

    • The pulmonary trunk branches into right and left pulmonary arteries, transporting blood to the lungs.

  • Left Ventricle:

    • Contracts to eject oxygenated blood into the aorta via the aortic semilunar valve.

    • The aorta processes blood to all body systems; the first branches are the two coronary arteries (left and right) supplying blood to the heart wall.

Cardiac Cycle

  • Description of blood flow:

    • Blood returns to the right atrium after oxygen delivery, through vena cavae and coronary sinus.

    • Semilunar valves prevent backflow during ventricular relaxation.

  • Duration of the cardiac cycle in an average adult at rest: 0.8 seconds.

Summary of Blood Flow Process

  • Atria fills with blood, AV valves open to fill ventricles.

  • Ventricles contract, AV valves close, and semilunar valves open to eject blood into the arteries.

  • Heart cycle is rapid, occurring continuously for sustenance of circulation.