Base Of Heart

Structure and Size of the Heart

  • The heart is a muscular, cone-shaped organ.
  • Dimensions: approximately 12 to 14 cm long and about 9 cm wide.
  • Weight: ranges from 250 to 350 grams.
  • Size comparison: roughly the size of a fist.

Positioning of the Heart

  • Located in the mediastinum, which is the medial cavity of the thorax.
  • Sits between the pleural cavities (each containing a lung).
  • Contains other structures: esophagus, trachea, large blood vessels.
  • Positioned on the superior surface of the diaphragm, posterior to the sternum, and anterior to the vertebral column.
  • External chest compression can aid in blood circulation (applicable in CPR).
  • About two-thirds of its mass lies to the left of the midline.

Base of the Heart

  • The superior portion is known as the base; it is the widest part and serves as an attachment point for large blood vessels.
  • The base lies posterior to the costal cartilage of ribs 2 and 3 and points towards the right shoulder.

Apex of the Heart

  • Formed by the tip of the left ventricle.
  • Typically located in the fifth intercostal space, just below the fifth rib pointing towards the left hip.

Pericardium

  • The heart is enclosed in a double-walled sac called the pericardium:
    • Parietal Pericardium: The outer layer made of tough fibrous tissue.
    • Protects the heart and anchors it to surrounding tissues (like the diaphragm).
    • Visceral pericardium (Epicardium): The inner layer that covers the heart's surface and produces pericardial fluid.

Pericardial Cavity

  • The space between the parietal pericardium and the epicardium is the pericardial cavity.
  • Contains 15 to 50 ml of pericardial fluid that reduces friction between the heart’s surfaces as it beats, preventing tissue damage.

Layers of the Heart Wall

  • Epicardium (or visceral pericardium): Thin outer layer.
  • Myocardium: Thick middle layer made up of cardiac muscle cells, blood vessels, and nerves.
  • Endocardium: Innermost layer made of flattened epithelial cells known as endothelial cells:
    • These cells form a smooth lining within the heart, cover the heart valves, and line the inner surface of blood vessels.
    • Smooth endothelial surfaces minimize friction, facilitating easy blood flow.