Human Heart structure and blood circulation (Includes heart diagram):

The heart is a very important organ of our body. Our existence is heavily dependent on the proper functioning of the heart. Any abnormality of the heart, even a minor problem with any part of the heart makes us suffer a lot with many different symptoms.

The structure and functions of the heart are really very difficult to understand. Even many medical students find it difficult to understand about the heart. But, we will try to make you understand the human heart structure with a simple heart diagram labeled.

We will try to provide more information about the four chambers of the heart, the valves of the heart, the layers of the heart, all the blood vessels connected to the heart like veins and arteries in the simplest possible manner.

Chambers of the heart (Atria and ventricles):

There are 4 chambers of the heart. They are further divided into 2 atria and 2 ventricles. Atria are further divided into the right atrium and left atrium. Ventricles are subdivided into the left ventricle and right ventricle.

The right atrium and right ventricle are thin and have thinner muscles in comparison to the left atrium and left ventricle. So, the pressure on the right side of the heart is less in comparison to the left side of the heart.

The right atrium receives the deoxygenated or the impure blood from the body and pumps it to the right ventricle. Then the right ventricle pumps the deoxygenated or impure blood to the lungs where it is purified or oxygenated.

Then the lungs send the oxygenated or pure blood back to the left atrium of the heart. The left atrium pumps the oxygenated blood to the left ventricle, which sends this blood to all the parts of the body through the great artery, the aorta.

Blood vessels connected to the heart:

Blood vessels play a vital role in carrying deoxygenated blood from the body to the heart and then to the lungs. They also carry the oxygenated blood from the lungs to the heart and then to all parts of the body.

Various arteries and veins are an important part of this entire process. Lets us look at the most important arteries and veins that maintain the proper functioning of the heart.

Arteries:

Arteries generally carry oxygenated blood throughout the blood. The biggest artery and the most important artery in the body is aorta. It is connected to the left ventricle and it carries oxygenated blood received from the lungs to all the parts of the body.

Also, the coronary arteries that originate from the aorta supply blood to the various layers and parts of the heart and help in maintaining proper function of this vital organ called the heart.

There is another important artery that originates from the heart. It is the pulmonary trunk or the pulmonary artery. It originates from the right ventricle. Pulmonary trunk or artery is the only artery in the body which carries impure or deoxygenated blood. It carries deoxygenated blood collected from all parts of the body to the lungs for purification or oxygenation.

Veins:

Generally, all the veins in the body carry deoxygenated or impure blood. Let us discuss some of the most important veins connected to the heart. The superior vena cava and the inferior vena cava collect deoxygenated blood from the organs of the body, including the chest, abdomen, head, upper and lower limbs through various branches and send it to the right atrium.

There is one exception to the veins, which are the pulmonary veins. There are four pulmonary veins which carry oxygenated blood from the lungs to the left atrium. They are the only veins carrying oxygenated blood.

There is another important vein called the coronary sinus. This vein is a union of various veins which collect deoxygenated blood from the myocardium or the cardiac muscle tissue. The coronary sinus then sends the deoxygenated blood to the right atrium, just like the other veins carrying deoxygenated blood.

Valves of the heart:

We have spoken about the four chambers of the heart and also about the various important blood vessels which are vital in maintaining the normal function of the heart. Let us speak about the valves of the heart which play a pivotal role in regulating the blood flow amongst these heart chambers and blood vessels.

Atrioventricular valves:

There are 2 atrioventricular valves in the heart. They are located at the junction of the atria and the ventricles. They are the Mitral or bicuspid valve and the tricuspid valve. The tricuspid valve is located between the right atrium and right ventricle. This valve is made up of 3 cusps or units just like its name suggests.

The mitral valve or the bicuspid valve is located between the left atrium and the left ventricle and it is made up of 2 cusps or parts. Both the Mitral valve and the tricuspid valve regulate blood circulation between the atria and the ventricles of the heart.

There are structures called chordate tendinae which attach the atria, both the right atrium and the left atrium to their respective ventricles. They help in maintaining the structural integrity of these valves when the heart contracts.

Chordae tendinae avoid the back flow of the blood from the ventricles to the atria. Proper functioning of this chordae tendinae prevents the development of conditions like mitral regurgitation or MR and tricuspid regurgitation or TR.

Semilunar valves:

The semilunar valves are located between the ventricles and the arteries connected to them. The semilunar valves called pulmonary valve is located between the right ventricle and the pulmonary artery.

The semilunar valve called aortic valve is located between the left ventricle and the aorta. Both the pulmonary valve or the pulmonic valve and the aortic valve have three cusps or parts. They are shaped just like a half moon or they are crescentic shaped. So, they are called semilunar valves.

The appropriate functioning of the semilunar valves is absolutely essential to prevent the development of certain heart ailments like pulmonary regurgitation or PR and aortic regurgitation or AR.

Layers of the heart:

We have spoken a lot about the heart chambers, the valves of the heart and also about all the major blood vessels connected to the heart. Now, let us also discuss the layers of the heart. There are three main layers of the heart.

They are the epicardium, the myocardium, and the endocardium. Let us look in a more detailed manner about all these three heart layers from inside out.

The endocardium:

The endocardium is the innermost layer of the heart. It is located just below the cardiac muscle tissue or the myocardium. The endocardium is made up of a type of cells which are flattened called squamous endothelium.

The endocardium is quite soft and smooth. This layer is in direct contact with the blood inside the heart. This layer prevents the adhesion of the blood to the heart layers and ensures smooth flow of blood. It prevents the formation of blood clots or coagulation within the heart.

The myocardium:

The myocardium is also called the cardiac muscle tissue. It is located just above the endocardium. This muscle tissue is very strong. The contractions of this layer of the heart or the myocardium help in pumping out blood from the heart to various body parts through the aorta and also to the lungs through the pulmonary artery.

The epicardium:

This is the outermost layer of the heart. It is located just above the myocardium. This layer of the heart is also called the innermost layer of the pericardium or the visceral pericardium. The pericardium is the structure that covers the heart and protects the heart. The epicardium is the layer of the heart that is mainly responsible for protecting the heart.

Conduction system of the heart:

We have seen the chambers of the heart, blood vessels, valves and also about the layers of the heart. But, do you know that there is a conduction system of the heart, which is responsible for generating the impulses which control the heartbeat?

The conduction system of the heart mainly consists of the SA node, AV node, Bundle of His, and the Purkinje fibers. The SA node or the Sinoatrial node is responsible for the generation of impulse that controls the heart rate or the heart beat.

So, it’s called the pacemaker of the heart. Then the impulse is spread through the atria and reaches the AV node or the atrioventricular node.

Then from there the impulse is spread to the Bundle of His. From there the heart impulse is spread to the Purkinje fibers and then to the entire myocardium. This impulse which is spread through the conducting system of the heart helps in the contraction of the heart which leads to the heart beat.

This conduction system of the heart is responsible for maintaining the heart rate at 72 beats for a minute. Any abnormality of this conducting system leads to disturbances of rhythm called arrhythmias. They can be bradyarrhythmias or tachyarrhythmias.

Diseases of the heart:

We have seen about the structure of the heart, the layers of the heart and also about the conduction system of the heart. Let us see some of the most important diseases of the heart.

Heart attack:

The heart attack is the common name of a disease called coronary artery disease. In this condition, the coronary arteries that we discussed above are blocked by plaques called atherosclerosis. This atherosclerosis develops due to various risk factors like hypertension, diabetes mellitus, smoking, alcohol, etc.

This atherosclerotic plaques block the blood supply to the heart and lead to the development of heart attack or the coronary artery disease.

Arrhythmias:

We have already spoken about the conduction system of the heart. Any abnormality in the conduction system of the heart leads to a condition called arrhythmias. There are many different types of arrhythmias, which are broadly classified into bradyarrhythmias and tachyarrhythmias.

There are many different types of arrhythmias like the stokes Adams syndrome, ventricular fibrillation, atrial fibrillation, atrial flutter, bradycardia, torsades de pointes, ventricular tachycardia, supraventricular tachycardia, etc.

Cardiomyopathy:

This is the heart ailment which affects the heart muscle or the cardiac muscle. The cardiac muscle tissue becomes very hard and stiff in cardiomyopathy. This impairs the pumping of the heart and hence the cardiac output too.

There are many types of cardiomyopathy like dilated cardiomyopathy, restrictive cardiomyopathy, and obstructive cardiomyopathy.

Myocarditis:

This is the swelling or the inflammation of the myocardium, the middle layer of the heart. It occurs due to various infections like bacteria and viruses.

Pericarditis:

This is the swelling or the inflammation of the pericardium, which is the outermost protective covering of the heart. This can also occur secondary to various infections like bacteria and viruses.

Pericarditis produces various symptoms like chest pain that changes with position, some sounds on auscultation like pericardial friction rub, etc.

Infective endocarditis:

This is the inflammation of the innermost layer of the heart, the endocardium due to infections. The people with prosthetic heart valves, any previous heart surgery, history of rheumatic heart diseases are more prone to develop this infective endocarditis.

IV or injection drug abusers can also develop this condition. This condition is really life threatening and has myriad symptoms.

Pulmonary embolism:

Certain people like women using oral contraceptive pills or OCP, people immobilized for a long duration due to surgeries or hospitalization, due to long flights, due to having hereditary clotting tendency are more prone to develop pulmonary embolism.

In this condition, a blood clot blocks the flow of blood from the right ventricle to the lungs. It leads t many symptoms like hypotension or low blood pressure, chest pain and shortness of breath or difficulty breathing.

Congestive heart failure:

Congestive heart failure or CHF is a condition in which the heart fails to pump blood due to various diseases. Many different heart diseases can culminate in CHF or congestive heart failure.

CHF can affect left heart that is left atrium and ventricle or the right heart, that is the right atrium and the right ventricle. The symptoms of the CHF depend on whether the left heart is affected or the right heart is affected.

You have seen about all the parts of the heart by using a simple and easy to understand heart diagram labeled properly. You people have also seen about the conducting system and also about some of the most important heart diseases.

The heart is a very important organ of the body which keeps us alive. So, try to eat healthy, avoid junk food, exercise regularly to maintain a healthy heart and ultimately a healthy life.