1.5 Internal Anatomical Features of the heart

Internal Anatomy of the Heart

• Sectioning and Direction

  • Important to recognize that internal anatomy of organs is often displayed in sections.

  • In this discussion, focus on a frontal plane (or coronal section) view of the heart from the anterior side.

• Return of Systemic Venous Blood

  • Systemic venous blood returns to the right atrium via:

    • Superior vena cava

    • Inferior vena cava

    • Coronary sinus

  • Additional contributor: Anterior cardiac vein.

• Flow from Right Atrium to Right Ventricle

  • Blood moves passively to the right ventricle, with some active movement to top off its volume.

  • Blood passes through the tricuspid valve (atrioventricular) to enter the right ventricle, marking the start of pulmonary circulation.

• Right Ventricle Contraction

  • When the right ventricle contracts, tricuspid valve is closed.

  • Pressure builds until the pulmonary valve opens, ejecting blood into the pulmonary trunk via pulmonary arteries.

• Gas Exchange in Lungs

  • In pulmonary capillaries, carbon dioxide (CO2) is released, and oxygen (O2) is absorbed.

  • Oxygenated blood returns through pulmonary veins to the left atrium.

• Path from Left Atrium to Left Ventricle

  • Blood flows through the bicuspid valve (or mitral valve) into the left ventricle.

• Internal Features of the Left Ventricle

  • Trabeculae carne: Bundles of cardiac muscle fibers extending into the ventricular volume, enhancing contraction leverage.

  • Papillary muscles: Connected to chordae tendineae, which anchor the AV valves (tricuspid and mitral).

    • The tension in these muscles correlates with ventricular wall tension, ensuring proper valve function during contraction.

  • Interventricular septum: The wall separating the left and right ventricles, composed of distinct tissue layers.

• Aorta and Systemic Circulation

  • Ejection from the left ventricle occurs through the aortic valve into the aorta.

  • Aorta sections include:

    • Ascending aorta

    • Aortic arch

    • Descending aorta

  • Major branches from aortic arch:

    • Brachiocephalic trunk: Supplies blood to the right arm, head, and neck.

    • Left common carotid artery: Supplies blood to the left side of the head and neck.

    • Left subclavian artery: Supplies blood to the left upper limb.

• Coronary Arteries

  • Heart receives its oxygenated blood supply via two coronary arteries branching off the aorta.

• Return of Systemic Blood

  • Blood returns via superior vena cava, inferior vena cava, and coronary sinus to the right atrium.

• Fetal Circulation Features

  • Fossa ovalis: Thinned section in right atrium from fetal circulation, later becomes a one-way valve.

  • Ligamentum arteriosum: Remnant of a fetal blood vessel that connected the aortic arch to the pulmonary trunk.

  • Connections necessary for fetal oxygenation through the placenta.

  • At birth, changes in pressure close the foramen ovale and constrict the ligamentum arteriosum, establishing normal heart circulation.

• Note on Fetal Circulation

  • A deeper discussion on fetal circulation to follow in subsequent lessons.