Left Atrium

Heart Anatomy

Left Atrium

Position, external features and internal features of the left atrium.

1

Position

  • The left atrium is a quadrangular chamber situated posteriorly.
  • It receives oxygenated blood from the lungs through four pulmonary veins.
  • It pumps blood to the left ventricle through the:
    • Left atrioventricular or bicuspid orifice
    • Mitral orifice
  • Bicuspid → Latin: two tooth point.
  • Mitral → Latin: like bishop’s mitre.
  • The orifice is guarded by the valve of the same name.
Bicuspid

Latin: two tooth point.

Mitral

Latin: like bishop’s mitre.

2

External Features

1 Left auricle

  • The appendage of the left atrium.
  • Projects anteriorly.
  • Overlaps the infundibulum of the right ventricle.

2 The left atrium forms

  • Left 2/3rd of the base of the heart
  • Greater part of the upper border
  • Parts of the sternocostal surface
  • Parts of the left surface
  • Left border

3 Posterior surface

  • The posterior surface of the atrium forms the anterior wall of the oblique sinus of pericardium.
3

Internal Features

1 Anterior Wall

  • The anterior wall of the atrium is formed by the interatrial septum.
  • The septal wall shows the fossa lunata.
  • It corresponds to the fossa ovalis of the right atrium.

2 Posterior Wall

  • Two pulmonary veins open into the atrium on each side of the posterior wall.

3 Smooth-Walled Part

  • The greater part of the interior of the atrium is smooth walled.
  • It is derived embryologically from the absorbed pulmonary veins which open into it.

4 Musculi Pectinati

  • Musculi pectinati are present only in the auricle.
  • They form a reticulum.
  • This part develops from the original primitive atrial chamber of the heart tube.

5 Tributaries

  • In addition to the four pulmonary veins, the tributaries of the atrium include a few venae cordis minimae.
Left Atrium — Study Notes