Synonym: Atrium
Definition
The heart has two atria, the right atrium and the left atrium. The atria are located in front of the respective ventricle and can be assigned to different blood circulations:
- The right atrium is part of the “small” circulation (pulmonary circulation)
- The left atrium is part of the “big” circulation (body circulation)
Anatomy of the left atrium
The atria are the “entrance hall” of the heart, so to speak: In the right atrium, the oxygen-poor blood collects from the veins to be pumped into the lungs via the right ventricle. There it is enriched with oxygen again. The left atrium (atrium sinistrum) is located upstream of the left ventricle and is therefore part of the large circulation (body circulation).
From the lungs, the blood, which is freshly saturated with oxygen, passes through the pulmonary veins (venae pulmonales) into the left atrium. Here it is collected in the relaxation phase of the heart, the diastole, until in the tension phase (systole) it flows via the left sail valve (the mitral valve) into the left ventricle. From here the oxygen-rich blood is distributed throughout the body via the aorta.
The right atrium receives the oxygen-poor blood from the body’s circulation and conveys it – via the tricuspid valve – to the right ventricle. From there, the blood is transported into the pulmonary circulation, where it is “loaded” with oxygen. It then passes through four pulmonary veins into the left atrium, from where it is transported – via the mitral valve – into the left ventricle.
From there, the oxygen-rich blood is pumped into the body’s circulation to supply the body with oxygen. The atria contribute to filling the ventricles with blood by contracting. There are, however, other mechanisms that play a larger role in filling the ventricles.
Clinical aspects
The atrial septum defect accounts for about 10% of congenital heart defects. In this case, there is a connection (shunt) between the left and right atrium even after birth. Whether such a defect causes discomfort to the person affected depends on how large this connection is, because the larger it is, the more blood can flow back and forth between the two atria: In pronounced cases, the high volume load on the pulmonary vessels leads to pulmonary hypertension (high blood pressure in the pulmonary vessels) with its serious consequences.
- In the case of minor defects, there are often no symptoms at all until adulthood,
- While larger defects can cause symptoms such as palpitations, shortness of breath during physical activity (exercise dyspnea) and reduced performance even in infancy.