In
anatomy, the
atrium (plural: atria), sometimes called
auricle (although, in the technical sense, the auricle is a separate part of the main atria known as the
atrial appendages), refers to a chamber or space. For example, the term is used for a portion of the lateral ventricle in the brain and the
blood collection chamber of the
heart. The atrium most commonly refers to a chamber in which blood enters
the heart, as opposed to the ventricle, where it is pushed out of the organ. It has a thin-walled structure that allows blood to return to the heart. There is at least one atrium in animals with a
closed circulatory system. In
fish, the circulatory system is very simple: a two-chambered heart including one atrium and one
ventricle. In other
vertebrate groups, the
circulatory system is much more complicated. Their circulatory systems are divided into two types: a three-chambered heart, with two atria and one ventricle, or a four-chambered heart, with two atria and two ventricles. The atrium receives blood as it returns to the heart to complete a circulating cycle, whereas the ventricle pumps blood out of the heart to start a new cycle.
Human heart
Humans have a four-chambered heart that includes the right atrium, left atrium, right ventricle, and left ventricle. The right atrium receives deoxygenated blood from the
superior vena cava,
inferior vena cava and
coronary sinus. The left atrium receives oxygenated blood from the
left and right pulmonary veins. The atria do not have valves at their inlets. As a result, a venous pulsation is normal and can be detected in the
jugular vein as the
jugular venous pressure.
Internally, there is the rough musculae pectinati and
crista terminalis, which acts as a boundary inside the atrium and the smooth walled part derived from the
sinus venosus. There is also a
fossa ovalis in the
interatrial septum, which is used in the
fetal period as a means of bypassing the lung.The atrium is depolarized by Calcium.
There are two atria, one on either side of the heart. On the right side is the atrium that holds blood that is deoxygenated. It sends blood to the right ventricle, which sends it to the lungs for oxygen. After it comes back, it is sent to the left atrium. The blood is pumped from the left atrium and sent to the left ventricle where it is sent to the aorta, which takes it to the rest of the body.
See also
Atrial syncytium
Atrial fibrillation
Ventricle (heart)
References
Category:Cardiac anatomy
