Viscera (heart, lungs, liver, gastrointestinal tract)
Left atrium
Atrium sinistrum cordis
- Origin
- Forms the posterior aspect and base of the heart, receiving oxygenated blood from the four pulmonary veins
- Insertion
- Opens anteroinferiorly through the left atrioventricular orifice guarded by the bicuspid (mitral) valve into the left ventricle
- Function
- Receives oxygen-rich blood from the pulmonary circulation and propels it into the left ventricle during atrial systole
- Innervation
- Cardiac plexus (sympathetic from T1-T4, parasympathetic via vagus nerve CN X)
- Movement & chain
- Atrial diastole (passive conduit and reservoir phase) and atrial systole ('atrial kick' contributing 15-20% of ventricular preload)
- Palpation
- Not directly palpable; assessed via echocardiography (TTE/TEE) and auscultation of the mitral area at the 5th intercostal space midclavicular line
- Clinical
- Atrial fibrillation commonly originates near pulmonary vein ostia, predisposing to left atrial appendage thrombus and embolic stroke. Left atrial enlargement in mitral stenosis.
- Segmental innervation
- T1-T4 dermatomes (cardiac referred pain to precordium and medial left arm)
- In clinical practice
- Anticoagulation therapy monitoring, cardioversion protocols, telemetry for rhythm analysis, left atrial appendage occlusion care
- Region in the model
- Viscera (heart, lungs, liver, gastrointestinal tract)