The Right Atrium.
The right atrium is the upper chamber on the right side of the heart. Previously, the atria were referred to as the auricles and the right atrium was referred to as the right auricle. The right atrium receives deoxygenated blood from the body through the superior vena cava and the inferior vena cava veins.
The superior vena cava brings blood from the head, neck and the upper extremities (upper part of the body) and the inferior vena cava brings blood from the chest, abdomen and the lower extremities (lower part of body). Once full, the right atrium contracts and pushes the blood into the right ventricle through the tricuspid valve.
Anatomy of Right Atrium.
The right atrium of the heart is separated from the left atrium by a wall of connective tissue which is called the interatrial septum.
The walls of the right atrium are thinner than those of the left atrium (about 2mm) as it has to pump blood against lower pressure than the left atrium.
The right atrium is irregular in shape, somewhat oblong with a shape of a cube. On its anterior side is a convexity which is called its sinus. On its superior side is an elongated muscular pouch which resembles an ear of an animal and hence the older name – auricle. This is called the right atrial appendage or the auricle of the right atrium.
The walls of the right atrium are made up of muscle fibers which are called musculi pectinati, because of their parallel pattern resembling the teeth of a comb. They give the right atrium a trabeculated surface.
Between the openings of the superior and inferior venae cavae is a small elevation which is called the tuberculum loueri.
The coronary vein, called the coronary sinus, which drains the walls of the heart opens directly in this chamber and its opening is guarded by the Valve of Thebesius.
The smooth walled portion that surrounds the openings of the superior and inferior vena cava and that of the coronary sinus is called the sinus venarum.
The opening between the right atrium and right ventricle is guarded by the tricuspid valve which has three cusps or leaflets and hence the name.
The opening of the superior vena cava has no valve while that of the inferior vena cava is protected by a partial valve called the Eustachian valve.
Interatrial Septum|Foramen Ovale.
The interatrial septum of the fetus has a hole in it during development. This connects the right atrium to the left atrium and is called the foramen ovale. In the fetus, blood flows from the right atrium into the left atrium bypassing the pulmonary circulation as the lungs do not function in the fetus. After birth, this opening closes and is then referred to as fossa ovale.
Sometimes, in some individuals, this opening does not close and is referred to as the atrial septal defect. As a result of this opening, blood flows from the left atrium to the right atrium resulting in lower output of the heart. This is potentially dangerous and causes cardiac failure. Untreated cases can result in death.
Picture showing right atrium and its interior.
Click on image to enlarge.
RA = right atrium| FO = foramen ovale| AV = AV node| VIVC = openings of venae cavae.
Function of Right Atrium|What Does Right Atrium Do.
The right atrium acts as a reservoir to receive deoxygenated blood from the superior and inferior veins and pumps it to the right ventricle which pumps it to the lungs for oxygenation.
The right atrium has baroreceptors on its inner surface which regulate the heart rate by slowing it when there is increased blood supply in the atrium and increasing the heart rate when the blood supply is low.
It also has an endocrine function. Due to the release of ANP (atrial natriuretic peptide hormone) when the atria are dilated, RA (and LA) also regulates heart rate.
Sinoatrial Node.
The sinoatrial node or SA Node is a specialized bundle of neurons (cells called myocytes) situated in the right atrium chamber next to the opening of the superior vena cava. It consists of impulse generating (pacemaker) tissue which generates the sinus rhythm. The SA node initiates the electric impulses in the heart which trigger cardiac contraction. The AV node is also situated in this chamber in the atrial septum between the right atrium and the right ventricle near the opening of the coronary sinus.
Blood Supply.
The blood supply to the walls of the right atrium is through the right coronary artery and drainage is through the coronary sinus.
Also read Left Atrium.
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