Corpus: Atrium

The atria' are the smaller cardiac cavities of the human heart located in front of the leaflets.

A distinction is made between:

• Right atrium (atrium cordis dextrum): Receives the deoxygenated blood from the superior vena cava and inferior vena cava and opens into the right ventricle via the tricuspid valve
• Left atrium (atrium cordis sinistrum): Receives oxygen-rich blood from the pulmonary veins and opens into the left ventricle via the mitral valve

Conical protrusions, the so-called auricles of the heart (auricula cordis), can be recognised on both atria.

Right atrium[Bearbeiten]

The right atrium receives the deoxygenated blood from the superior and inferior vena cava as well as the coronary sinus, the anterior cardiac veins and the minimal cardiac veins and pumps it into the right ventricle. The inferior vena cava flows into the right atrium in the ostium venae cavae inferioris, the superior vena cava in the ostium venae cavae superioris.

Morphology[Bearbeiten]

The muscle wall thickness is usually approx. 3 mm. Morphologically, two sections can be distinguished on the inside of the atrium:

• An uneven, rough surface, which essentially lines the right auricle (auricula dextra). This is caused by the protruding muscle ridges (pectinate muscles) that traverse the entire lumen.
• The smooth-walled surface of the sinus venarum cavarum between the superior and inferior vena cava, which serves as the flow surface of the venous blood.

The boundary of these two surfaces is represented externally by the sulcus terminalis, which corresponds internally to a crista terminalis muscle ridge.

Besonderheiten[Bearbeiten]

The following anatomical structures can be found in the right atrium of the heart:

• Septum atrioventriculare: small area above the tricuspid valve where the right atrium borders the left ventricle; consists of an anterior pars membranacea and a posterior pars muscularis
• Ostium sinus coronarii: opening of the coronary sinus at which the valvula sinus coronarii (a small elevation) is located directly
• Fossa ovalis: derivative of the foramen ovale, which is surrounded by a bulge, the limbus fossae ovalis
• Valvula venae cavae inferiores (Valvula Eustachii): elevation ventral to the junction of the inferior vena cava, which continues the limbus fossae ovalis caudally. During the foetal period, it conducts the blood into the open foramen ovale. Distally, the valvula merges into the Todaro tendon.
• Sinus node: It is located near the ostium venae cavae superioris at the sulcus terminalis and is the superior centre of the excitation formation system of the heart
• AV node: It is located in the so-called triangle of Koch and is downstream of the sinus node as the centre of excitation formation or conduction.
• Torus aorticus: small wall protrusion created by the initial part of the aorta
• Tuberculum intervenosum: slightly pronounced protrusion on the posterior wall of the right atrium

Left atrium[Bearbeiten]

The left atrium receives oxygen-rich blood from the 4 pulmonary veins, which are valveless at their confluence, and pumps it into the left ventricle of the heart. Apart from the left atrial appendage, the left atrium is barely visible on the ventral side and lies mainly dorsally, on the base of the heart.

The wall thickness of the left atrium is about 3 to a maximum of 4 mm. The majority of the surface of the left atrium is smooth. Only the inner surface of the auricula sinistra is fissured due to the unevenness caused by the pectinate muscles.

In the interatrial septum, the fossa ovalis is covered by the valvula foraminis ovalis, a derivative of the septum primum atriorum, which lies postnatally over the foramen ovale.

The atria serve to temporarily store the blood and thus enable a continuous venous return flow to the heart. If the large body veins were to attach directly to the ventricle, the venous return flow would be interrupted during systole. With the help of the atria, the heart can increase its output by around 75%, which makes the heart work much more economically.

The two atria draw blood from the vena cava or the pulmonary veins and pass it on to the ventricles through the atrial contraction. The contractions are incomplete and dimensioned in such a way that the venous inflow is not interrupted. The active filling of the ventricles by the atria is particularly important at higher heart rates.

Diagnostics[Bearbeiten]

The size of the atria can be examined during echocardiography. The left atrium is measured planimetrically or volumetrically in the four-chamber view and the left atrial area (LAA, LAF) or left atrial volume (LAV) is calculated from this. The following reference values apply:^[1]

Pathologies[Bearbeiten]

Pathological changes in the atrial region include atrial aneurysm, atrial septal aneurysm (ASA), accessory auricle and atrial diverticulum.