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Explain the Internal Structure of Human Heart

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Human Heart

The heart is one of the most important organs in the human body. It is the main organ of the pulmonary system. Structurally, the human heart is a very complex muscular bag which is separated by a septum. It is located in the upper thoracic cavity at the centre of our chest in between the lungs. The heart lies above the diaphragm and behind the sternum. It is estimated that the size of an individual's heart is roughly equal to the size of his closed fist. The heart of a fully-grown healthy individual weighs about 200-300 gm.

The Functions of The Heart

The heart plays a crucial role in the survivability of a human. No wonder, it has a complex structure with four compartments. The heart receives deoxygenated blood from the entire body and pumps it to the lungs. The oxygenated blood from the lungs again enters the heart from where it is pumped to the different parts of the body. The heart undergoes cycles of contraction and relaxation. These rhythmic movements provide the force necessary for the blood to move around the different parts of the body through blood vessels. 

Structure of The Heart

The human heart is covered externally by a thick muscular covering called the pericardium. Below the pericardium, there is a parietal layer made up of serous membrane. There is also another layer of visceral serous membrane. The visceral layer is a part of the epicardium. The internal structure of the heart is fairly complex. The heart is a muscular bag made of a special type of muscle called the cardiac muscle. These muscles are made up of highly branched units of fibres that help the heart in contraction and relaxation. The outer layer of the heart is made up of three layers: 

1) The outer epicardium

2) The middle myocardium 

3) The inner endocardium

The heart has four chambers and is divided into two sides, the left side and right side, by a septum or muscular wall. The left side receives deoxygenated blood of the body while the right side receives oxygenated blood. Each side of the heart is again further divided into two parts. The upper smaller chamber is called the auricle or articular. The lower comparatively larger chamber is called ventricles. Therefore, in total, the heart has four chambers, the right auricle, right ventricle and the left auricle and left ventricle.

The walls of the atria are comparatively thinner than the walls of the ventricle. This is because the ventricles need more force to pump the blood to distant parts of the body whereas the ventricles only require enough force to push the blood to small proximity.

There is a septum which divides the auricular compartment into distinct right auricle and left auricle. This septum is nothing but a thin muscular partition. It is known as the inter-arterial septum (inter arterial mean in between the auricles). The ventricles are also separated by a similar partition. This partition is named the inter-ventricular septum. The interventricular septum is, in contrast to the inter-auricular septum, thick-walled. Both the inter-auricular and interventricular septum have the common function of preventing the oxygenated blood from getting mixed up with the deoxygenated blood. 

In the hearts of lower vertebrates like fishes and reptiles, the heart is not four-chambered. The auricles and ventricles are not separated by a proper septum. This results in mixing of oxygenated and deoxygenated blood.

The atria and ventricles, in turn, are separated by a septum. It is called the auriculo-ventricular septum. The point where the right auricle opens into the right ventricle, a valve is present there. The valve present on this site is trifurcated and is known as the tricuspid valve. On the other side of the heart, the left auricle opens into the left ventricle at similar positions. This opening, in turn, is guided by another valve. This valve is called the bicuspid valve. This valve is bifurcated. Both of these valves serve the function of opening and closing in a systemic manner so that there is no backflow of blood. 

Deoxygenated blood from all over the body is pumped into the right auricle. From there the blood flows into the right ventricle through the tricuspid valve. From the right ventricle, there is the pulmonary artery which carries this deoxygenated blood from the ventricle to the lungs. In lungs the blood gets oxygenated. The oxygenated blood is poured into the left auricle. From left auricle, the blood travels to left ventricle from where it leaves the heart through the aorta. 


The heart is one of the most important organs in our body. Regular exercise, a healthy diet and a fresh mind keep the heart in a healthy condition. We must take good care of our heart as even a minute cardiac problem can bring forth a series of issues, sometimes, even leading to death. A healthy heart is essential for the wellbeing of a person.