Chambers of the Heart

Anatomy and Physiology of the Heart - Part 2

The heart consists of four chambers: The right and left Atrium, and the right and left Ventricles.

The Atrium is connected to Ventricles via valves and the right and left sides are separated by a septum.

Right Atrium:

The Right Atrium consists of the main chamber and the Right Atrial Appendage. Venous (deoxygenated) blood drains/enters into the Atrium from the whole body (excluding the lungs) via three sources:

1. The Inferior Vena Cava - From the lower part of the body.
2. The Superior Vena Cava - From the upper part of the body.
3. The Coronary Sinus - From the heart muscle itself.

*There is also a remnant of a small fetal blood tube connecting between the right and left atrium called the Fossa Ovalis, which closes, by most, at birth.

From the Right Atrium to blood flows to the Right Ventricle through the Tricuspid Valve (named after the three leaves from which the valve is composed of).

Right Ventricle:

• The right ventricle constitutes most of the (anterior) front surface of the heart.
• Between the right and left ventricles there is a dividing wall named the Interventricular Septum.
• The walls of the right ventricle are much thicker than the walls of the Atrium, and it is possible to identify ligaments of muscles commonly called trabeculae carneae. These muscles divide into three specific types, and the most important for us are the Papillary muscles.
• There are 3 papillary muscles in the right Ventricle. These muscles are connected on one end to the wall of the heart, and the other end attached to the strings that connect to the Tricuspid Valve.
• The ligaments between the valves leaves and the papillary muscles are called chordae tendineae.

From the Right Ventricle, Venous (deoxygenated) blood flows to the pulmonary trunk, which is a large artery that splits into two Pulmonary Arteries, right and left, one for each lung. Blood reaches the lungs through the pulmonary valve, the Pulmonary (Semilunar) Valve, is named after its leaves which are in the shape of a half moon.

Left Atrium:

•  The Left Atrium has a structure similar to the right one (main chamber and the Left Atrial Appendage).
• In the posterior wall of the Left Atrium are four Pulmonary Veins (usually 2 on the right side and 2 on the left), that deliver oxygenated blood from the lungs to the left side of the heart to supply oxygen throughout the body. These veins have no valves.

The blood is transferred to the Left Ventricle via the Mitral (Bicuspid) Valve (named after the two leaves from which the valve is composed of).

Left Ventricle:

• The walls of the Left Ventricle are 3 times thicker than those of the Right Ventricle (the blood pressure here is 6 times higher than the right side).
• The muscles of the Trabecula Cornea (as described in the Right Ventricle) are highly developed and there are only two Papillary Muscles for the two leaves of the Mitral (Bicuspid) Valve.
• From the Left Ventricle, the blood flows to the Aorta that pumps blood to the periphery (the rest of the body and the heart itself).
• The transition to ascending aorta is through the Aortic (Semilunar) Valve.