The heart is the body’s epicenter of life activity. No larger than the size of a fist, the heart is hollow, divided into four basic chambers, and the most important muscle in the human body. In an adult female, the heart weighs about 225 grams. In an adult male the heart weighs approximately 310 grams. With 42 million contraction annually, the heart pumps about 700,000 gallons of blood through the human body.


Between the lungs in the thoracic cavity there is another cavity known as mediastinum. This is where the heart is positioned. From the center of the human body, approximately 2/3 of the heart is positioned to the left. A cone shaped end known as the apex rests downward, protruding down into the diaphragm. The large blood vessels connect to the heart at the superior broad end which is considered the heart’s base. Dense fibrous connective tissue that surrounds and protects the heart is known as the parietal pericardium. Visually speaking the pericardium appears much like a loose sac around the muscle. It is filled with fluid known as pericardial fluid. This sac is also responsible for forming the wall of the pericardial cavity, segregating the heart from the rest of the thoracic organs. The parietal pericardium is comprised of two layers, the fibrous outer layer, and the inner serous layer. The inner layer creates the fluid that encompasses the heart, permitting it to beat without friction or tension. This fluid allows the heart to beat in a state of suspension.


Image: Heart

Three layers create the outer wall of the heart. The epicardium is also called the visceral pericardium and creates the outermost layer of the heart wall. The pericardial cavity is created by this layer and the parietal pericardium. The myocardium is the middle layer of the heart wall. This thick layer is comprised of muscle which is squeezed and wrung as the heart beats. The more force required to eject the blood from the chamber of the heart the thicker this layer becomes throughout the heart. The left ventricle of the heart has a very thick layer of myocardium while the thin layers of the atrial wall indicate less required pressure. The endocardium of the heart wall makes up the inner layer. The endothelium of blood vessels creates unity and continuity with this inner layer of the heart’s wall. Heart valves are covered with the endocardium. The medical condition known as endocarditis is the inflammation of the endocardium layer of the wall of the heart.


The heart is made up of four interior chambers. There are two upper and two lower chambers which create the muscle. The atria are the upper right and left chambers and the ventricles create the lower right and left chambers. The atria both contract at the same time as do the lower chambers, creating almost a see saw like pumping action of upper then power contractions. When the atria contract they empty their contents into the lower ventricles.

Pestinate muscles are muscles which line the atria. They look like lacey lattice along the lining of the interior muscle wall. The auricle is the additional appendage that expands in the shape of an ear from the atria.

Each chamber is its own separate entity. The atria maintain their separation with a thin wall known as the interatrial septum, which is a muscular element inside the heart. The ventricles maintain their separation via a much thicker muscular wall known as the interventricle wall. Atrioventricular valves segregate the atria from the ventricles. There are two large blood vessels exiting the heart muscle which are partitioned with valves known as the semilunar valves. All heart valves are designed to ensure that the blood flow only travels in one direction.


Chambers and Valves
Image: Chambers And Valves

The surface of the heart has visible depressions which have contain the grooves associated with the blood vessels which supply the heart muscle with its own oxygenated blood. These depressions indicate the individual chambers of the heart. The division between the atria and the ventricles also marks the coronary sulcus which circles around the heart. It is also the most prominent and obvious grooved depression on the heart muscle. The anterior and posterior interventricular sulci mark the obvious segregation of the right and left ventricles.

The right side of the heart (both the ventricle and the atrium) is responsible for receiving the blood flow which has little oxygen and distributing it toward to the lungs. The left ventricle and atrium receive the blood which is high in oxygen and discharges it for distribution to the rest of the body.


The superior vena cavity drains the used blood from the upper half of the body and funnels into the right atrium. The inferior vena cavity drains the used blood from the lower half of the body and repeats the process, funneling the deoxygenated blood into the right atrium. The heart also distributes the used blood from the myocardium via the coronary sinus opening which funnels into the right atrium.


The atrioventricle valve is also known as the tricuspid valve. This valve is responsible for the transfer of blood from the right atrium into the right ventricle. The tricuspid valve is denoted by three cusps which are individually held in place via the tendons called the chordae tendineae. These tendons are held fast to the wall of the ventricle via the papillary muscles which are coned shaped muscles. When the ventricles contract the pressure within the ventricles naturally increases and these valves need support to prevent the inversion of the valve. This is where the muscles and tendons come into play.

When blood leaves the right ventricle via muscle contraction, the tricuspid valves close. The blood passes through the pulmonary trunk and passes through the right an left pulmonary arteries to fill the lungs’ capillaries. Positioned at the base of the pulmonary trunk is the pulmonary semilunar valve. It is the responsibility of this valve to prevent backwash of the blood back into the right ventricle post ejection.


While the blood is within the capillaries of the lungs, the blood gases are exchanged, creating a higher retention of oxygen. The freshly oxygenated blood then traverses the two left and two right pulmonary veins and travels into the left atrium.


Once the blood has entered the left atrium it is contracted and ejected into the left ventricle. The valve which the blood travels through is called the left atroiventricular valve, and more commonly known as the mitral valve. This valve opens when the left ventricle is relaxed and open to blood flow. The mitral valve closes when the left ventricle enters a state of contraction. Receiving oxygenated blood from the left atrium, the left ventricle contracts, and the mitral valve prevents any backwash of blood to return to the left atrium.

The left ventricle works harder than the right ventricle and thus is designed with a thicker wall. The left ventricle is the portion of the heart responsible for pumping oxygenated blood throughout the entire body.

The endocardium of the left and right ventricles are marked uniquely by the presence of ridges called trabeculae carneae. The aorta extends downward from the left ventricle, taking with it the newly oxygenated blood to be distributed throughout the entire body. At the bottom of the descending segment of the aorta there is a valve known as the aortic valve. When the left ventricle is between contractions, the aortic valve shuts off the blood flow in order to prevent it from backwashing and returning into the left ventricle. The aortic valve is also medically termed the aortic semilunar valve.
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