Introduction

Heart is a vital organ of our body that keeps on beating, pumping blood which carries oxygen and nutrients to various vital organs and carries back carbon dioxide and other gases and by-products for elimination. It keeps on working throughout our life without getting tired. Recent changes in the dietary and lifestyle habits in the society have been the cause for various lifestyle diseases. The major effect of unhealthy lifestyle and poor dietary habits is on heart. The kind of food we eat has a tendency to deposit on the walls of the blood vessels which increases the blood pressure and causes increased load on the heart. To understand it in a better way we should know how heart functions and how altered lifestyle or increased load on heart can cause health risks.

What makes the human heart?

Heart is located in the chest cavity. It is almost the size of fist and located in the rib cage slightly on the left side of the sternum or the breast bone in the notch of the left lung. It is a completely muscular organ and is made of specialized cardiac muscles. These muscles are unique in that they are fused to one another as a subunit and have multiple nuclei. Heart pumps blood to all the organs of the body. Cardiac muscles work throughout the life and don’t get fatigued.

The heart is enclosed in a double layered sac called the pericardium. The pericardium has pericardial fluid between the two layers of the pericardium. It acts as a shock absorber and also prevents friction when heart and lungs contract and relax.

Heart has four chambers or compartment- left and right atrium and left and right ventricles. The atrium collects the blood from the body and ventricles supply blood to different organs. The right and left atrium and ventricles are separated by muscular septum. The natural pacemaker of the heart is SA node, these electrical impulses causes the atrium to contract. This contraction of the atrium causes the blood flow to ventricles .The gateway to ventricles is maintained by valves. The tricuspid valve controls the blood flow from right atrium to right ventricle and mitral valve controls the blood flow between left atrium and left ventricles. The contraction of ventricles occurs when electrical impulses reach AV node from SA node. AV node causes the contraction of ventricles resulting the blood flow to various organs. There is pulmonary valve between right ventricle and pulmonary artery and aortic valve between left ventricle and aorta. Valves prevent the backflow of blood and maintain the unidirectional flow of blood.

What are the different kinds of blood vessels?

For the complete circulation to take place there are different kinds of blood vessels that form a network all over the body. The network of blood vessels is highly specialised as there are different blood vessels for carrying blood from heart to different parts of the body and back to heart. The different kinds of blood vessels are-

1. Arteries

   These are the blood vessels that carry blood from heart to various organs. They start from the large artery aorta leaving the heart and become smaller as they branch out further reaching various organs of the body. They are highly elastic and oxygenated blood flows through them except pulmonary artery that carries deoxygenated blood.

2. Veins

   Veins are the blood vessels that carry blood from various organs to the heart. Veins have less elasticity than arteries and start getting wider in as they approach heart. Deoxygenated blood from head, upper body and arms is brought to blood by superior vena cava and deoxygenated blood from abdomen and lower limbs is brought to heart by inferior vena cava.

3. Capillaries

   Capillaries are the blood vessels that connect the arteries and veins. They are thin walled than arteries and veins and are least elastic. The pressure of blood is also least in capillaries. They help in gaseous exchange, delivery of nutrients and passage of waste products in the blood stream due to the thin wall and higher permeability.

How does the heart function?

Now when we know what makes up the human heart and what are the different kinds of blood vessels that carry blood from heart we can now better understand the functioning of heart.

The heart’s main function is to pump blood to all organs of the body. It works both ways by carrying oxygenated blood and nutrients to various organs of the body and to carry waste products and deoxygenated blood back to heart. The Heartbeats by the action of SA node which is the natural pacemaker of the heart. SA node is located in the right atrium and sends electrical impulses to both the atrium for the contraction. It occurs at a regular interval, heart beats 60-80 times per minute in a healthy individual at rest.

The contraction of atrium causes the unidirectional flow of blood to the ventricles. Meanwhile the electrical impulses travel from SA node to the AV node. AV node is located in the lower side of the right atrium. There is a specialised bundle of fibres located at AV node which transmits the signals to the ventricles. This bundle of fibres is known as AV bundle, it further divides into a fine network of fibres all over the ventricles which are known as the purkinje fibres. The transmitted electrical impulses cause the contraction of ventricles. The contraction of ventricles causes the flow of blood to the pulmonary artery and aorta. The pulmonary artery carries the deoxygenated blood from right ventricle to the lungs and the aorta carries the oxygenated blood from left ventricle to other parts of the body.

The heart circulates the blood via two pathways:

1. The pulmonary circuit
2. The systemic circuit

Pulmonary circuit

In pulmonary circuit the deoxygenated blood leaves the right ventricle of the heart via pulmonary artery and is carried to lungs. The contraction of ventricle pushes the blood in the pulmonary artery and valves prevent the backflow of blood in atrium. The gaseous exchange takes place and the deoxygenated blood now becomes the oxygenated blood. Now the oxygenated blood is carried to the left atrium via the pulmonary vein. The circuit is called pulmonary circuit because it involves the passage of blood from heart to the lungs and then back to heart.

Systemic circuit

The contraction of left atrium due to action of SA node causes the blood to reach left ventricle. In systemic circuit the oxygenated blood leaves the left ventricle via aorta and is taken to various parts of the body via arteries and capillaries, this blood is rich in oxygen and nutrients. The contraction of left ventricle pushes the blood in aorta and valves prevent the backflow of blood in atrium. The gaseous exchange takes place and metabolic wastes are also discarded in blood. Now this deoxygenated blood is taken to the right atrium via superior and inferior vena cava.

Once the blood reaches right atrium whole cycle is repeated again. It is a cyclical process and is carried throughout our life till we die.