Chapter 12 Heart I External and Internal Features

Chapter 12: Heart I - External and Internal Features

Introduction to the Heart

  • Location: Conical, hollow muscular organ located in the middle mediastinum.

  • Enclosed by: Pericardium.

  • Size: Approximately the size of a clenched fist, with dimensions of 12 cm in length and 8-9 cm in width.

  • Weight:

    • Adult males: ~300 g

    • Adult females: ~250 g

  • Structure: Composed of four chambers: right atrium, right ventricle, left atrium, and left ventricle.

Blood Flow Through the Heart

  • Right Atrium:

    • Receives deoxygenated blood from superior and inferior venae cavae.

    • Transfers blood to the right ventricle.

  • Right Ventricle:

    • Passes deoxygenated blood to the lungs via the pulmonary trunk.

  • Left Atrium:

    • Receives oxygenated blood from the lungs through four pulmonary veins.

    • Transfers blood to the left ventricle.

  • Left Ventricle:

    • Supplies oxygenated blood to the entire body via the aorta.

External Features of the Heart

  • Borders:

    • **Base (posterior surface)

    • Right Border

    • Left Border

    • Inferior border**.

  • Surfaces:

    • Anterior/Sternocostal Surface

    • Inferior/Diaphragmatic Surface

    • Left Surface

    • Right Surface

Heart Morphology

  • Shape: Conical (Pyramidal).

  • Dimensions:

    • Length: 12 cm

    • Width: 8-9 cm

  • Weight:

    • Achieved between ages 17-20 years.

Apex of the Heart

  • Location: Directed downward, forward, and to the left; lies in the fifth left intercostal space, medial to the midclavicular line.

  • Formation: Primarily formed by the left ventricle, overlaps by the left lung.

Base (Posterior Surface) of Heart

  • Shape: Quadrilateral, opposite to the apex of the heart.

  • Relations: Separated from the vertebral column by various structures including:

    • Oblique sinus

    • Fibrous pericardium

    • Principal bronchi and esophagus.

Left and Right Atria

  • Right Atrium:

    • Receives blood from the superior vena cava, inferior vena cava, and coronary sinus.

    • Features:

      • External: Elongated, conical shape; includes right auricle with notched margins; sulcus terminalis along the right heart border.

      • Internal: Composed of sinus venarum, pectinate part, and interatrial septum with important openings guarded by valves.

  • Left Atrium:

    • Receives oxygenated blood from the four pulmonary veins; divided into:

      • External: Forms the left 2/3 of posterior surface, has a left auricle, and ventricular groove.

      • Internal: Smooth surface, receives blood through pulmonary veins, features fossa lunata corresponding to the fossa ovalis of the right atrium.

Right Ventricle

  • Features: Thick-walled triangular chamber that receives blood from the right atrium and sends it to the pulmonary trunk.

  • Internal Structure: Divided into inflow part with trabeculae carneae and papillary muscles, and outflow part or infundibulum leading to the pulmonary valve.

Left Ventricle

  • Features: Conical, thick-walled chamber. Receives oxygenated blood from the left atrium and pumps it into the ascending aorta.

  • Internal Structure: Circled in cross section with inflow and outflow parts; papillary muscles connect to the mitral valve.

Clinical Integration

  • Apex Impulse: Observable in the fifth intercostal space, representing the outer thrust of the apex during ventricular systole.

  • Pathologies: Conditions such as atrial septal defects (ASDs), ventricular septal defects (VSDs), and Tetralogy of Fallot significantly impact heart function.