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The Heart: An Introduction to One of the Major Organs

Last updated date: 29th Jan 2023
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The heart is a muscular organ. This organ circulates blood through the circulatory system's blood vessels. Pumped blood transports oxygen and nutrients to the body while transporting metabolic waste like carbon dioxide to the lungs. In humans, the heart is about the size of a closed fist and is located in the middle compartment of the chest, between the lungs.

Every day, our heart does amazing things. Every cell in the human body, except the cornea, receives blood from the heart. In the United States, heart disease is the leading cause of death. That is why it is critical to take care of the heart by living a heart-healthy lifestyle.

The Human Heart

The heart is a small organ that circulates blood throughout our body. It is our circulatory system's primary organ. The heart functions as two pumps, one on each side, which work in tandem. Blood flows from the right atrium to the right ventricle, then to the lungs to be oxygenated. Blood flows from the lungs to the left atrium, then to the left ventricle. Our heart's primary function is to keep oxygenated blood circulating throughout our body.

Structure of the Heart

  • As it can be seen in the structure of the heart diagram, our heart is composed of four chambers: two small upper chambers called atria and two bigger bottom chambers called ventricles.

  • The ventricle walls are significantly thicker than those of the atria.

  • The interatrial septum is a thin, muscular wall that separates the right and left atria, whereas the interventricular septum is a thick-walled wall that separates the right and left ventricles.

  • The atrioventricular septum is a strong fibrous structure that divides the atrium and ventricle of the same side. However, each atrioventricular septum has an opening through which the two chambers on the same side are joined.

  • The chordae tendineae are unique fibrous cords that are linked to the flaps of the bicuspid and tricuspid valves at one end and to the ventricular wall at the other end, with specific muscles termed papillary muscles.

  • Three semilunar valves are present, where the pulmonary artery (which arises from the right ventricle and transports deoxygenated blood to the lungs) and aorta (which arises from the left ventricle and transports oxygenated blood to other regions of the body) leave the heart. These valves keep blood from returning to the ventricles.

  • Deoxygenated blood enters the right atrium via the coronary sinus and two big veins known as vena cava as shown in the image of a labelled diagram. Through two pairs of pulmonary veins, the left atrium gets oxygenated blood from the lungs.

Parts of Human Heart

Well Labelled Diagram of The Heart

  • Right atrium, right ventricle, left atrium, left ventricle, tricuspid valve, mitral valve, pulmonary valve, aortic valve, superior vena cava, inferior vena cava, pulmonary trunk, right pulmonary artery, left pulmonary artery, pulmonary veins, and aorta etc. form the main part of the heart.

Layers of The Human Heart

Pericardium: Pericardium is the membrane that surrounds and protects the heart. It limits the heart to its mediastinum location while providing enough mobility for robust and fast contraction.

Fibrous Pericardium: Tough, inelastic, thick, and uneven connective tissue. It protects the heart and anchors it in the mediastinum by preventing overstretching.

Serous Pericardium: It is a thinner, more sensitive membrane that forms a second layer surrounding the heart. The fibrous pericardium is linked to the outer parietal layer. The inner visceral layer, also known as the epicardium, is one of the layers of the heart wall that adheres tightly to the surface of the heart. The pericardial fluid is found in the area between the parietal and visceral layers, and the region that contains this lubricating secretion of pericardial cells is known as the pericardial cavity.

The heart's wall is made up of three layers: the epicardium (external layer), the myocardium (middle layer), and the endocardium (inner layer).

Epicardium: It is the clear outermost layer. It is made up of mesothelium and fragile connective tissue, which gives the surface heart a smooth, slippery touch.

Myocardium: The middle layer of cardiac muscle tissue that makes up around 95 per cent of the heart. It is responsible for its pumping activity. The cardiac muscle is an involuntary muscle.

Endocardium: The deepest layer, is a thin layer of endothelium that is covered by a thin layer of connective tissue. It creates a smooth lining for the heart chambers and valves. It is continuous with the endothelial lining of big blood arteries connected to hearts and reduces surface friction as blood flows through the heart and blood vessels.

Chambers of The Heart

The heart is made up of four chambers, as seen in the labelled diagram of the heart. The atria (entrance halls or chambers) are the two superior receiving chambers, while the ventricles (little bellies) are the two lower pumping chambers. An auricle is a wrinkled, pouch-like structure on the front surface of each atrium.

1. Right Atrium:

  • The right atrium is located on the heart's right side and receives blood from three veins: the superior vena cava, inferior vena cava, and coronary sinus.

  • The posterior wall is smooth, but the anterior wall is rough due to the presence of pectinate muscles, which extend the auricle.

  • The interatrial septum is a thin partition between the right and left atriums.

2. Right Ventricle:

  • The right ventricle is roughly 4-5 mm thick on average and makes up the majority of the heart's anterior surface.

  • The right ventricle is divided from the left ventricle by an internal barrier known as the interventricular septum.

  • The pulmonary valve (pulmonary semilunar valve) directs blood from the right ventricle into the pulmonary trunk, which separates into right and left pulmonary arteries.

  • Arteries are usually responsible for transporting blood away from the heart.

3. Left Atrium:

  • The left atrium is roughly the same thickness as the right atrium and makes up the majority of the heart's base.

  • It gets blood from the lungs via four pulmonary veins.

  • The interior of the left atrium, like the right atrium, has a smooth posterior wall.

  • Since pectinate muscles are restricted to the left atrial auricle, the anterior wall of the left atrium is likewise smooth.

  • The bicuspid valve, which has two cusps, allows blood to flow from the left atrium into the left ventricle.

4. Left Ventricle:

  • The left ventricle is the thickest chamber of the heart, usually 10-15 mm in thickness, and serves as the heart's apex.

  • The left ventricle, like the right, features trabeculae carneae and chordae tendineae that connect the bicuspid valve cusps to papillary muscles.

  • Blood flows from the left ventricle into the ascending aorta via the aortic valve.

Functions of The Heart

  • The cardiac cycle, which is the heart's blood-pumping cycle, ensures that blood is dispersed throughout the body.

  • The oxygen distribution process begins when oxygen-free blood enters the heart through the right atrium, travels to the right ventricle, enters the lungs for oxygen replenishment and carbon dioxide release, and then returns to the left chambers for redistribution.

  • When a cardiovascular condition is detected, the heart's function can be checked. A heart-related ailment, for example, is characterised by a consistently irregular heartbeat or beats per minute. This is because a heartbeat is a representation of the heart's two-phase oxygen-reloading mechanism.


Every minute of a 24-hour day, our heart beats anywhere from 60 to 100 times. It beats roughly 100,000 times per day. But, unlike the other muscles in our bodies, our heart almost never gets tired until it stops completely. Our heart does amazing things, and we have studied the structure of the heart diagram with parts and different muscles which form the heart. This article provides important information about its functioning. Our heart is helping us stay healthy, we must take care of it. From an exam point of view, one must practise heart structure with labelling. Human heart diagram and functions are frequently asked in the examination.

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FAQs on Heart

1. Which layer of the heart functions as a protective layer?

The pericardium is a double-walled membranous sac that protects the heart. The pericardium is made up of two layers: an exterior parietal pericardium and an inside visceral pericardium, both of which are linked to the heart. Between the two layers is a gap called the pericardial cavity, which is filled with pericardial fluid. The pericardium protects the heart from mechanical and electrical shocks.

2. Describe the four valves of the heart and their function.

Heart valves are parts of the heart that open and close to allow blood to pass from one part of the heart to another. A well-labelled heart diagram showcases these valves properly. The four valves of the heart are listed below:

  • Aortic Valve: The aortic valve has three leaflets. They open to allow blood to flow from the left ventricle of your heart to the aorta. This transports oxygenated blood from the heart to the rest of the body. The aortic valve prevents aortic backflow into the left ventricle.

  • Mitral Valve: The mitral valve has two leaflets. They allow blood from the lungs to pass into the left atrium. Furthermore, they inhibit backflow from the left ventricle to the left atrium.

  • Pulmonary Valve: The pulmonary valve contains three leaflets as well. They allow blood to be transported from the right ventricle to the pulmonary artery. This artery transports blood to the lungs, where it picks up oxygen.

  • Tricuspid Valve: This has three leaflets. They facilitate blood flow from the right atrium to the right ventricle. They also keep blood from returning from the right ventricle to the right atrium.

3. Which vein transports oxygenated blood from the lungs to the heart?

Veins are blood veins that transport blood to the heart. The pulmonary vein transports oxygen-rich blood from the lungs to the heart. The pulmonary vein is the sole vein that delivers oxygenated blood to the heart; all other veins deliver deoxygenated blood.

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