The Left Atrium

• • The left and right pulmonary veins carry oxygen rich blood from the lungs to the left atrium. Blood flows from the left atrium through the left AV valve into the left ventricle.
• Oxygen enters the bloodstream at the pulmonary capillaries
• The oxygen rich blood, also called oxygenated blood, flows from the pulmonary capillaries into small veins
• Four pulmonary veins, usually two for each lung
• These left pulmonary veins and right pulmonary veins empty into the posterior portion of the left atrium
• Left atrium differs from the right atrium

  • left atrium is more cuboidal in shape
  • left auricle is longer, narrower, more hook shaped
  • all the pectinate muscles of left atrium are contained within the left auricle
• As blood flows from the left atrium into the left ventricle, it passes through the left atrioventricular (AV) valve, also known as the mitral or bicuspid valve
• The bicuspid valve permits the flow of oxygen rich blood from the left atrium into the left ventricle, but prevents blood flow in the reverse direction