Human Biology: Understanding the Heartbeat and Cardiac Cycle

The human heart is a very complex organ that is responsible for transporting blood throughout the body. Without a functioning heart, oxygen rich blood would not be able to circulate throughout the body. The heartbeat, or cardiac cycle, is how the heart pumps blood throughout the body's tissues. When the heart beats, both the left and right atria contract and then relax. At the same time, ventricles are doing the same thing, which is how blood is pumped in and out of the heart.

A contraction is known as a systole, while a diastole is when the heart relaxes after having experienced a contraction. The heart valves open and close so that blood is forced to move in only one direction. When this occurs, it makes a unique sound, known as a lub-dub, which can be heard when using a stethoscope. Each ventricular system also has one unique pulse. A pulse is the pressure that is passed when blood is pumped from the heart to the arteries. Additionally, humans have an SA, or sinoatrial, node that acts as a pacemaker for keeping the hearts rhythm on track. This node is responsible for letting the atria know that it should contract. This happens very frequently, typically occurring every not even a second apart. The AV, or atrioventricular, node receives these signals and is responsible for letting the ventricles know that they should contract. However, a person's nervous system and certain hormones can change the heart's rhythm.

In order for doctors to help see and record the cardiac cycle, the electrocardiogram, or ECG, was invented. An ECG helps by recording the electrical changes that happen in the wall of the heart when the cardiac cycle takes place. An ECG can help doctors see and diagnose a wide variety of heart conditions and abnormalities. For example, a ventricular fibrillation occurs when the ventricles contract at different times. Machines like a defibrillator can help stop these problems, but they do not always work. Heart conditions are a very serious problem and need to be checked out by a cardiologist as soon as you believe that something is wrong.

Source:

Benitz, Bill. Lecture: Human Biology. November 9, 2009