The Heart |
The heart is the main organ of the circulatory system. It beats approximately 100,000 times a day and draws about 13,000 litres of blood. For a human to be alive their heart needs to be beating constantly. These beats are created by the successive contractions and relaxations of the myocardium (cardiac muscle tissue). The normal heart rate for adults ranges from 60 to 100 beats per minute. Women almost always have a quicker heart rate than men (more beats per minute), while the heart rate of babies during their birth can reach 130 beats per minute. The function of the heart depends on other factors, like events happening to the rest of the body, as well. Some of these events could be intense physical activity, when the heart needs more blood, therefore increasing the rhythm of its functions. This last process is called self-regulation.
Contrary to popular belief, the heart isn't completely on the left side of the human body. Instead, it is tilted slightly towards that side and located in the middle of the chest, slightly behind and to the left of the breastbone (sternum), in between of the two lungs. In fact, the left lung isn't as big as the right one for the heart to fit on the left side of the body.
The heart is an organ of conical shape which consists of cardiac muscle tissue, the myocardium. Its size is similar to a big fist.
The human heart is constituted of four chambers. The lower two chambers are called the ventricles and the upper two are called the atria. The antria have thin walls and the ventricles have thicker ones (the left one is much thicker since it is made of a lot more myocardium in order to be able to send blood from there to the entire body). The two ventricles are seperated by the ventricular septum, while the two atria are seperated by the atrial septum. Thus, there is no direct connection between the two ventricles and atria. In between of the atria and the ventricles are valves which make sure there is a one-way blood flow after each contraction of the heart, preventing backflow.
The heart receives oxygen-poor blood with a large concentration of carbon dioxide and, through a process which involves all of its chambers and the lungs, turns it into oxygen-rich blood and pumps it to the entire body. This process happens in the order below: