Here are some facts about human heart.
The heart is basically a hollow muscular pump, which pushes the blood through out the body via the blood vessels. A normal sized healthy heart is roughly the same size as a fist. It is located between the lungs and slightly to the left of center. The heart is an involuntary muscle that has approximately seventy to ninety contractions per minute during a restful state. It begins to pump early in the life of a fetus and will continue unceasingly until death.
A hollow organ, the heart’s walls are made up by three distinct layers. They are as follows:
1. Endocardium (en-do-kar’de-um) this is a very smooth layer of cells that form the interior membrane of the heart. The endocardium tissue is also the type of tissue that makes up the valves of the heart.
2. Myocardium (mi-o-kar’de-um) is the actual muscle tissue of the heart and is by far the thickest layer.
3. Pericardium (per-I-kar’de-um) is the outermost layer of the heart and is also the tissue that serves as the lining of the pericardial sac.
The main portion of the heart is split into two different sides with an actual partition called the septum. Each side of the heart works as a separate pump and have two chambers apiece or as a whole, the heart has four distinct chambers.
1. Right atrium is the thin-walled area that receives the venous or “used” blood returning to the body by the veins.
2. Right ventricle is the “pump” area of the heart’s right side. The atrium dumps the blood into the ventricle where it is then pumped out the pulmonary arteries and to the lungs.
3. Left atrium receives the oxygenated blood returning from the lungs.
4. Left ventricle has the thickest walls of all. It is from this chamber the blood is pumped out of the heart, into the aorta and out to the rest of the body.
Since blood flow needs to be a one-way affair, there are valves at the entrance and exit of each ventricle. The entrance valves are called atrioventricular (a-tre-o-ven-trik’u-lar) and the exit valves are semilunar (sem-e-lu’nar). Each of the actual valves has it’s own specific name though.
1. Tricuspid valve is the one located at the entrance of the right ventricle. It prevents the blood from washing back into the right atrium. It gets its name from the three “cusps” or flaps that make up the valve.
2. Pulmonary semilunar valve is located between the right ventricle and the pulmonary artery.
3. Mitral valve is made of very heavy cusps and is located at the entrance of the left ventricle. This is a powerful valve that closes as the left ventricle begins each of its contractions to ensure the oxygenated blood doesn’t re-enter the left atrium.
4. Aortic valve is located, as its name would imply, between the left ventricle’s exit and the aorta itself.
Even though the heart is split up into two distinct halves, these two must work together to function properly.
When the heart starts to contract, it begins in the upper (atrium), thin-walled chambers and causes the blood to be squeezed out into the lower (ventricle) chambers. As the upper chamber finishes its squeeze, the lower chamber begins its work. The active action of these two chambers working together is called systole (sis’to-le). Each of these active periods will be followed by a short resting period known as diastole (di-as’to-le) although the heart never actually stops.
As the walls of the atrium complete their contraction, the ventricle begins its active stage. As the ventricle has been contracting the atrium has been filling up with blood so the entire process begins anew.
The sound of a normal heartbeat has often been described as “lubb” and “dupp”. The “lubb” period is the longer and deeper sounding of the two and is made as the ventricle is in its systole period. It is thought the sound is a result of the thick muscled walls of the ventricle contracting and the atrioventricular valves slamming shut. The “dupp” sound is shorter and has a distinctively sharper pitch. It occurs during the ventricle’s diastole period and is made as the semilunar valves close.
When these valves are not functioning normally there is a “swooshing” sound that can be heard. These are caused by the blood backwashing into the various chambers of the heart and are one of the possibilities when health care professionals are speaking of “murmurs.”
If a spinal or some other type of injury occurs and the nerves to voluntary muscles are cut, that muscle ceases to work and the area becomes paralyzed. Amazingly, if the nerves to the heart are cut it will continue to beat. The reason for this is that even though the heart is controlled by the nervous system, the heart’s muscles can actually contract rhythmically on its own. Unfortunately the nervous system is required for the heart to beat rapidly enough to maintain proper blood flow. If the nerves were to be cut, the heart’s rate could drop below 40 beats per minute and even if activity is increased, the heart’s rate would not.
The human heart is a fascinating organ that many, if given the chance, would love to exam. For most this possibility will never become a reality but for the really curious, there is an adequate substitute. This substitute is the heart of the common cow and can usually be obtained by visiting a local meat market and asking for one.
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