Introduction to the Heart
The heart is the pump station responsible for circulating blood throughout the human body. It is about the size of a clenched fist and sits in the chest cavity between the two lungs. Its walls are made up of muscle that can squeeze or pump blood out every time the organ "beats" or contracts. Fresh, oxygen-rich air is brought to the lungs through the trachea, or windpipe, every time that you breathe. The lungs are responsible for delivering oxygen to the blood, and the heart circulates the blood to the lungs and different parts of the body.
The heart is divided into FOUR chambers. The upper chambers are known as atria while the lower chambers are referred to as ventricles. The right atrium (RA) sits on top of the right ventricle (RV) on the right side of the heart while the left atrium (LA) sits atop the left ventricle (LV) on the left.
The right side of the heart is responsible for pushing blood to the lungs, where red blood cells pick up fresh oxygen. This oxygenated blood is then returned to the left side of the heart. From here, the oxygenated blood is transported throughout the whole body, supplying the fuel that the body cells need to function. The blood cells of the body extract or remove oxygen from the blood. The oxygen-poor blood is returned to the right atrium, where the journey began. This round trip is known as the circulation of blood.
Between the right atrium (RA) and the right ventricle (RV), there is an opening known as the tricuspid valve. It has three flexible thin parts, known as leaflets, that open and shut to regulate the flow of blood. When shut, the edges of the three leaflets touch each other to close the opening to prevent blood from leaving the RV and going back into the RA. Thus, the tricuspid valve serves as a trapdoor valve that allows blood to move only in one direction - from RA to RV. Similarly, the mitral valve allows blood to flow only from the left atrium to the left ventricle. Unlike the tricuspid valve, the mitral valve has only two leaflets.
Attached to the edges of the mitral and tricuspid valves, there are thin thread-like structures stretching downwards. These chords or strings are known as chordae tendineae. They connect the edges of the tricuspid and mitral valves to muscle bands or papillary muscles. The papillary muscles shorten and lengthen during different phases of the cardiac cycle and keep the valve leaflets from flopping back into the atrium. The chords are designed to control the movement of the valve leaflets similarly to ropes attached to the sail of a boat. They allow the sail to bulge outwards in the direction of a wind but prevent them from helplessly flapping in the breeze. They also allow the leaflets to open and shut in a given direction, but not beyond a certain point.
When the three leaflets of the tricuspid bulge upwards during contraction, or emptying of the ventricles, their edges touch each other and prevent backward flow to the right atrium. This important feature allows blood to flow through the heart in only ONE direction, and prevents it from leaking backwards when the valve is shut. The two leaflets of the mitral valve function in a similar manner and allow flow of blood from the left atrium to the left ventricle, but close and cut off backward leakage into the left atrium when the left ventricle contracts and starts to empty.