The heart is composed of four cavities, two ventricles and two atria. The atrium is also called the cardiac atrium or atrium cordis.
What is the atrium of the heart?
The heart is a hollow muscular organ responsible for supplying blood to the entire body. The human heart is located in the pericardium in the mediastinum. In shape, it resembles a rounded cone. The average human heart is the size of a fist and weighs between 230 and 350 grams, depending on gender. In its general structure, the heart is formed by two halves. The right heart and the left heart each consist of a ventricle and an atrium. In a healthy heart, blood always flows through the atrium into the ventricle. From there, depending on the side of the heart, it enters either the large or the small circulatory system. If the muscles of the atrium are damaged, atrial flutter or atrial fibrillation may occur.
Anatomy and structure
The fist-sized heart can be divided into right and left halves. The two sides of the heart are in turn divided into ventricles and atria. The ventricles are also called the ventricles and the atria are called the artria. The spaces of the heart are separated by the cardiac septum. The septum that lies between the two atria is called the atrial septum (interatrial septum). The septum between the two ventricles is called the ventricular septum (septum interventriculare) or the ventricular septum. To ensure that blood can only flow in one direction at a time between the atria and the ventricles, heart valves are located between the atria and the ventricles and between the ventricles and the blood vessels. All valves are located on one level. This plane is called the valve plane. The right atrium is separated from the right ventricle by the tricuspid valve. Between the left atrium and the left ventricle is the mitral valve. The wall of the atria consists of three different layers. Inside is the inner lining of the heart (endocardium). This is a very thin epithelial layer that lines the entire interior of the heart and also forms the heart valves. The middle layer is the cardiac muscle layer, the myocardium. The myocardium is responsible for the contraction of the heart. The excitation system, which controls the heart’s action, is also located here. The outer layer of the heart, the epicardium, forms the pericardium.
Function and tasks
The function of the heart, and therefore the function of the atria, is to supply the body with oxygenated blood. The superior and inferior vena cava flow into the right atrium. They carry the deoxygenated (venous) blood from the systemic circulation to the heart. The right atrium collects this blood and passes it through the tricuspid valve to the right ventricle in atrial systole. From there, the blood enters the pulmonary arteries via the truncus pulmonalis. In the pulmonary circulation, the blood is enriched with oxygen. It flows via the pulmonary veins into the left atrium. As the atrium fills, the ventricles simultaneously eject blood into the arteries. The right and left atria always fill at the same time and also always contract at the same time. As soon as the ventricular muscles relax, the valves open. As a result of the pressure drop in the ventricles and a slight contraction of the atrium, blood flows from the left atrium into the left ventricle. From there, in the next systole, the blood enters the aorta and thus the large systemic circulation. For the heart to contract at all, electrical excitation is required. The electrical excitation of the heart is controlled by a special excitation conduction system with pacemakers. The excitation begins in the sinus node. This is located in the muscles of the right atrium between the right heart ear and the superior vena cava. The excitation initially spreads through the two atria. These contract just before the ventricles. Subsequently, the excitation reaches the AV node. This is located in the valvular plane. The excitation is then transmitted via the His bundle and the Tawara bundle to the so-called Purkinje fibers.
Diseases
Excitation conduction in the heart is regulated by the autonomic excitation system. The heart’s top pacemaker, the sinus node in the right atrium, determines the rhythm. But before the impulse reaches the ventricles, it must pass through the AV node. This filters the impulses and can act as a brake. Damage to the atrial musculature can lead to disturbances in excitation formation and conduction.The damage is usually caused by coronary heart disease (CHD), in the context of heart failure, by valvular heart disease or by high blood pressure. Increased alcohol consumption and hyperthyroidism are also possible causes of damage to the atrial muscles. In atrial flutter, the atria are stimulated up to 350 times per minute; in atrial fibrillation, the rate is as high as 600 beats per minute. The resulting uncoordinated blood flow causes blood to remain in the atria. This can lead to life-threatening complications. Blood stasis develops, which can lead to the formation of blood clots. Thus, 48 hours after existing atrial fibrillation, there is an increased risk of thrombosis. If the clot forms in the left heart, it enters the large systemic circulation and can thus cause a stroke or mesenteric infarction. Thrombi from the right heart reach the lungs, where they can cause pulmonary embolism. Despite the threat of life-threatening complications, the arrhythmias often go unnoticed or become noticeable only as heart stuttering or slight palpitations. More than 95 percent of cases of the disease, however, are readily treatable.