Heart Chambers
Introduction to Heart Chambers
Previously, we highlighted the heart’s role as a dual pump, essential for circulating blood across the body and through the lungs.
The heart is divided into four chambers: two atria and two ventricles: The right atrium and the left atrium, followed by the right ventricle and the left ventricle
The right atrium receives blood from the body’s lower region through the inferior vena cava and from the upper region through the superior vena cava. These veins, along with the coronary veins, are tasked with returning blood to the heart.
The left atrium receives blood from the lungs via the pulmonary veins
The Atria
General Functions
The atria act as auxiliary pumps for the ventricles. When the ventricles are in a state of relaxation, known as diastole, the atria contract (enter systole), actively pushing blood into the ventricles to prepare for the next expulsion of blood from the heart. To achieve this they are strategically placed behind the ventricles.
The atria are two in number the right atrium and the left atrium.
Right atrium
The right atrium receives blood from the lower part of the body through the inferior vena cava, and from the upper part of the body through the superior vena cava. Another set of veins, known as the cardiac (coronary) veins, carries blood from the myocardium, which is the heart muscle, and returns it to the heart.
Left atrium
The left atrium receives blood via the pulmonary veins. These veins bring oxygenated blood back to the heart.
The Ventricles
General Functions
The ventricles are pivotal components of the heart, serving as its main pumps. Their primary function is to propel blood throughout the body. This propulsion is achieved through a mechanism known as ventricular systole, during which the ventricles contract, pushing blood out in the great arteries. Essentially, the ventricles generate the force needed for the circulation of blood.
Right ventricle
The right ventricle is the main pumping chamber on the right side of the heart. It has a crucial role, positioned so that it makes up the anterior surface of heart and part of the inferior surface of heart. Its most important job is to send deoxygenated blood to the lungs via the pulmonary artery.
Left Ventricle
Conversely, the left ventricle is tasked with pumping oxygenated blood to the rest of the body through the aorta. Situated anterior to the left atrium, the left ventricle is also notable for forming the apex of the heart.
Valves of the Heart
Prevent backflow.
As you might have noticed by now, blood moves in one direction, from the atria into the ventricles. When the ventricles contract, the pressure inside them increases, pushing the blood into the great arteries (the aorta and the pulmonary artery, respectively). An important fact is that when the ventricles contract, the blood is not pushed back into the atria; and when the ventricles relax, the blood stays in the great arteries and doesn’t fall back into the ventricles. The question then is, how is this achieved?
This is possible due to the presence of two sets of unidirectional valves, which will be described in greater detail later. For now, it’s worth mentioning that they are grouped into two main categories: the atrioventricular and semilunar valves
Atrioventricular (AV) Valves
The Atrioventricular (AV) Valves are positioned at the junctions where the ventricles meet the atria. These valves ensure blood flows smoothly from the atria into the ventricles. There are two atrioventricular valves: the right AV (Tricuspid) valve and the left AV (Mitral) valve.
Semilunar Valves
The Semilunar Valves are located at the junctions where the ventricles connect to the great arteries—the pulmonary artery and the aorta. Their primary function is to prevent backflow into the ventricles during diastole. On the right side of the heart is the Pulmonary valve, and on the left side is the Aortic valve.
Fibrous Skeleton
The heart’s valves, essential for directing blood flow, are supported by a critical structure, a connective tissue frame known as the fibrous skeleton. This framework plays a pivotal role, particularly for the Atrioventricular valves, by providing the necessary support and stability. Made entirely of connective tissue, as we will se in greater detail later, the fibrous skeleton uniquely isolates the ventricles from the atria while also maintaining a connection between them.