Overview
The heart is the most important muscular organ in the body. It works around the clock pumping blood to various parts of the body through the network of blood vessels. The normal adult heart weighs between 200- 425 grams (7 to 15 ounces) and is about the size of your fist. Learning about your heart and its functions can help you understand the various conditions that may affect your heart as well to take precautions to prevent them.
The heart is located between the right and left lungs in the middle of your chest. The heart’s function is to supply oxygen and blood to all parts of the body. Oxygenated blood pumped from the heart reaches the body’s organs through the systemic arteries, while veins carry impure or deoxygenated blood back to the heart.
The heart has four muscular chambers, the upper two chambers are called the right and left atria, and the lower two chambers are called the right and left ventricles.
For better understanding, the structures of the heart are discussed under two sections — external anatomy and internal anatomy.
External Anatomy
The external view of the heart shows many structures. Every structure is associated with certain function which is important for normal functioning of the heart. Let us learn more about these structures.
Pericardium: The pericardium is a fluid filled sac that encloses the heart and the ends of its major blood vessels including the aorta, vena cava and pulmonary artery. The pericardium is made of three layers:
- Outer fibrous sac–fibrous pericardium,
- Middle layer–parietal pericardium
- Inner layer–visceral pericardium
The space between the parietal and visceral layer is called the pericardial cavity and is filled with pericardial fluid. The pericardial fluid acts as a lubricant to allow normal heart movements within the chest and acts as a shock absorber to protect the heart from trauma.
Arteries and Veins
Aorta: The aorta, the largest blood vessel in the body, carries oxygen rich blood from the left ventricle to the various parts of the body.
Vena Cava: The superior vena cava and inferior vena cava are the two largest veins in the body. The superior vena cava returns deoxygenated blood to the right atrium from the upper part of the body. The inferior vena cava brings de-oxygenated blood from the lower part of the body to the right atrium of the heart.
Pulmonary artery and pulmonary veins: The pulmonary artery transports the de-oxygenated blood from the right ventricle to the lungs for oxygenation. The oxygenated blood is then carried to the left atrium through the pulmonary veins.
Coronary arteries and coronary veins: Coronary arteries originate from the ascending aorta and deliver oxygen-rich blood to the heart muscles. Coronary veins remove deoxygenated blood from the muscular tissue of the heart and drain it into the right atrium.
Internal Heart Anatomy
Muscular chambers: The heart has four muscular chambers, the upper two chambers are called the right and left atria, and the lower two chambers are called the right and left ventricles.
The right atrium collects the de-oxygenated blood from the vena cava and delivers it to the right ventricle. This delivery is regulated by the tricuspid valve. The right ventricle delivers the blood to the lungs for purification (oxygenation). This delivery is regulated by the pulmonary valve.
The left atrium collects the oxygenated blood from the lungs via the pulmonary veins and delivers it to the left ventricle. This delivery is regulated by the mitral valve. The left ventricle then delivers the oxygenated blood to the aorta (main artery) from where it is pumped to the rest of the body. This delivery is regulated by the aortic valve.
Heart Valves: Heart valves are flap-like structures that allow blood to flow in one direction preventing backward flow of the blood.
The heart has four valves:
- Tricuspid Valve: It is located between the right atrium and the right ventricle.
- Mitral Valve: It is located between the left atrium and the left ventricle.
- Pulmonary Valve: It is located between the right ventricle and the pulmonary artery.
- Aortic Valve: It is located between the left ventricle and the aorta.
Circulatory System
The heart works as a pump to deliver blood to every organ, tissue, and cell of your body through a complex network of arteries, arterioles, and capillaries. Blood returns back to the heart through venules (small veins) and veins.
The circulatory system has two parts:
Pulmonary circulation: During pulmonary circulation, the pulmonary artery carries de-oxygenated blood from the heart to the lungs for oxygenation and returns oxygenated blood back to the heart through the pulmonary veins.
Systemic circulation: In systemic circulation, the aorta carries oxygenated blood from the heart to all the organs of the body through the systemic arteries, and returns de-oxygenated blood back to the heart via the systemic veins.
Conduction System
The heart muscle consists of an electrical conduction system that triggers the heart walls to contract. The system is made of two nodes (special conduction cells) and a series of conduction pathways.
Sinoatrial or SA node: Also, called the pacemaker of the heart, the SA node is located in the upper wall of the right atrium. The SA node is responsible for setting the rate and rhythm of the heart beat causing the atria to contract when the electrical impulse is released. The signal then passes to the atrioventricular (AV) node.
Atrioventricular (AV) node: Located between the atria and ventricles, the AV node checks the signal and sends it to the conduction pathways (bundle of His) to provide electrical stimulus to the ventricles.
Bundle of His: This is a group of fibres located within the septum of the heart that carries electrical impulses from the AV node to the ventricles. It is divided into right and left bundle branches. These bundle branches are further divided into tiny filaments, known as Purkinje fibres. These fibres connect directly to the cells in the walls of your heart’s left and right ventricles to maintain regular contraction.
A healthy heart is important for overall well-being. Certain disease conditions and lifestyle habits such as smoking, being overweight, and leading a sedentary life can put your heart at risk affecting how it functions and leading to complications. Heart disease is preventable and the actions you take to reduce your risk of heart disease by making lifestyle changes will increase your chances for a long and healthy life.
