The heart is vital in vertebrate bodies, as its primary role is to generate the pressure needed to circulate blood throughout the entire body.

Our heart is approximately the size of our clenched fist, broader at the top and tapering towards the bottom. Positioned on the left side within the chest cavity between the lungs, it consists primarily of myocardium, a muscle tissue capable of rhythmic contraction and relaxation.

The healthy heart beats regularly, maintaining a consistent rhythm known as the heart rate, which averages between 60 to 80 beats per minute in adults. Alongside frequency, the heart also adheres to a specific rhythm. Any deviation from this regular pace, whether too fast or slow, indicates an abnormal heart rhythm.

Heart Function

The heart serves as the engine of the human body, primarily tasked with pumping blood. The left heart pumps oxygen-rich blood through the arteries into the aorta and its branches, supplying vital organs with oxygen and nutrients. Conversely, the right heart collects oxygen-poor venous blood, sending it to the lungs where it absorbs oxygen. This oxygenated blood returns to the heart and is pumped out again as arterial blood to nourish the body's tissues.

The heart also plays a regulatory role, adjusting to the body's varying demands for blood flow by altering the rate and force of its contractions. For instance, during exercise or moments of heightened emotion, the heart accelerates to enhance delivery of oxygen and energy to meet increased demands.

Key Structures

The heart is composed of myocardium and four chambers: the left atrium, left ventricle, right atrium, and right ventricle. Among these chambers, the left ventricular wall is the thickest. These chambers facilitate systemic circulation, where oxygenated blood is pumped throughout the body, and pulmonary circulation, where deoxygenated blood travels to the lungs for oxygenation.

The left and right atria, as well as the left and right ventricles, are separated from each other by septa. Between the atria and the ventricles are atrioventricular valves, which permit blood to flow only from the atria into the ventricles, preventing backflow.

Atrium

The heart has two atrium: the left atrium and the right atrium. The left atrium receives oxygenated blood from the lungs via the pulmonary veins, which it then pumps into the left ventricle to be distributed to tissues and organs throughout the body as part of systemic circulation. On the other hand, the right atrium receives deoxygenated blood from the body through the superior and inferior vena cavae. It pumps this blood into the right ventricle, which then sends it to the lungs for oxygenation as part of pulmonary circulation.

There is a small, specialized nodule located on the right atrium of the human heart called the sinus node. Composed of special cells, the sinus node generates electrical impulses spontaneously and rhythmically. These electrical signals travel throughout the heart, causing the cardiomyocytes (heart muscle cells) to contract and relax in a coordinated manner. This process originates the normal heartbeat of the human body.

Ventricles

The heart has two ventricles: the left ventricle and the right ventricle. These chambers are primarily responsible for pumping blood out of the heart to the lungs and the rest of the body.

Valves

The function of valves in the heart is to ensure that blood flows in one direction, preventing it from flowing backward.

The valve between the left atrium and left ventricle is known as the mitral valve, and the valve between the right atrium and right ventricle is called the tricuspid valve.

Additionally, the valve between the left ventricle and the aorta is called the aortic valve, and the valve between the right ventricle and the pulmonary artery is known as the pulmonary valve.

Circulation

The circulation of blood through the heart and all blood vessels is known as blood circulation, which is divided into two main parts: systemic circulation and pulmonary circulation, based on the pathways through which blood travels.

Blood flows in one direction through the heart, moving from the left and right atria into the left and right ventricles. From there, the left ventricle pumps blood into the aorta, while the right ventricle sends blood into the pulmonary arteries. This directional flow ensures that blood is distributed throughout the body via the arteries.

Pulmonary Circulation

Pulmonary circulation refers to the path that blood takes as it flows from the right ventricle into the pulmonary artery, then through the capillary network within the lungs, and finally returns to the left atrium via the pulmonary veins. This process allows for the exchange of gases—oxygen entering the bloodstream and carbon dioxide being released—within the lungs.

Systemic Circulation

Systemic circulation refers to the circulation of blood from the left ventricle into the aorta, which then carries it through arteries, capillary networks, and veins throughout the body's tissues and organs. Eventually, the blood returns to the heart via the superior and inferior vena cavae, entering the right atrium to complete the circulation cycle.

Coronary Arteries

The coronary arteries, which traverse the heart's surface, supply oxygen and nutrients to the heart muscle cells, ensuring their proper function. All organs in the human body, including the heart, require a blood supply from the arterial system.