The human Heart
The Heart – The Engine of Life
The circulatory system carries vital oxygen, water, nutrients and hormones through our bodies. Our “engine” – the heart – keeps this system running. The fist-sized muscle weighs 300 grams (10.5 ounces) and is located in the center of the chest, slightly to the left, protected by the breastbone (sternum) and ribs. In the span of one minute, the heart pumps all of our blood through the entire body with rhythmic contractions. Over one’s lifetime, the heart beats three billion times and transports 250 million liters of blood – an astonishing performance that no other engine can compete with.
The Sinus Node Sets the Heartbeat
Two sounds that can be heard with a stethoscope make up the heartbeat. One sound – the systole phase – is the heart chambers contracting and pumping blood into both circulatory systems. This lasts about one third of a second. The diastole phase – the second sound – is the atria contracting when the lower heart chambers are empty. It lasts approximately two thirds of a second. When the atria are full, the lower chambers are empty, and vice versa.
The sinus node, a plexus in the right atrium, starts the contractions. From there, the impulse travels into the chambers. These electrical currents can be seen with an electrocardiogram (ECG or EKG). The physician uses the ECG to evaluate if the heart is healthy and working well, and see if the patient has previously suffered a heart attack.
The brain and nervous system control the heart. The electrical impulses that create the heartbeat come from the heart itself. The heart will beat as long as it is supplied with oxygen, even if that oxygen is supplied externally, for example during a heart transplant.