PARTS OF THE HEART AND THEIR FUNCTIONS: STRUCTURE, ARTERIES, VEINS - ANATOMY AND PHYSIOLOGY - 2025

The parts of the heart such as the ventricles, atria, valves, septa or nodules are those that make this organ work so that it can pump blood through the body, to all organs and tissues.

It is about the size of a fist, is a hollow cavity shaped like a "cone" and is located in the middle-left area of ​​the chest, just between the lungs. It belongs to the cardiovascular system, which is the set or network of veins and arteries through which blood circulates.

Diagram of the anatomy of the human heart (Source: Diagram_of_the_human_heart_ (cropped) _pt.svg: Rhcastilhosderivative work: Ortisa via Wikimedia Commons)

This muscle receives systemic blood (from organs and tissues), pumps it to the lungs for oxygenation, and then receives this oxygenated blood from the lungs to pump it to the rest of the body, sending oxygen and nutrients to the cells of the body.

The endocardium, myocardium, and epicardium are the three layers that make up the wall of the heart. In addition, it is surrounded by a membranous "sac" known as the pericardium, which also contains a liquid that lubricates it during its movement.

Layers of the heart: epicardium (outer layer) myocardium (middle layer) and endocardium (inner layer) / Photo retrieved from web.as.uk.edu.

The hollow chambers of the heart are four, two atria and two ventricles. The atria join the ventricles and are separated from the ventricles by valves, just as valves separate the ventricles from the veins with which they connect.

The contraction and relaxation of the heart muscle depends on a special group of cells that is responsible for the generation and conduction of electrical impulses from the atria to the ventricles. These cells are in structures called nodes and fascicles.

Parts of the human heart

The heart is made up of four chambers, which make up two pumps (ventricles), a left and a right, which are connected in series, as if it were a circuit.

The four chambers of the heart are made up of myocardial tissue (heart muscle).

- Atria

The atria are the upper chambers of the heart, there is a right and a left and they are chambers with more or less thin walls, which support little pressure.

They are considered "booster pumps" and each one is associated, in its lower part, with a ventricle. However, more than "pumps", they function as blood reservoirs for their respective ventricles.

These chambers contract before the ventricles and both do so almost in unison (at the same time). Its contraction facilitates the emptying of the blood inside it to fill the ventricles with which they connect.

- Ventricles

Blood flow in the heart: a) On the left, diastole movement. The chambers are relaxed, allowing blood to enter the human body. b) In the middle, atrial systole and ventricular diastole. The atria contract, sending blood into the ventricles. c) On the right, atrial diastole and ventricular systole. The atria relax and the ventricles contract, pumping blood out of the heart. / Photo recovered from newhealthaisha.com

The ventricles are the two lower chambers of the heart and are the true "pumps" that project blood to the lungs and the rest of the body's organs and tissues.

Like the atria, there are two ventricles, one left and one right, and each connect with the left and right atria, respectively.

These chambers are made up of numerous muscle fibers, which are responsible for the contraction that propels blood out of the ventricles.

The atrium and right ventricle are responsible for receiving systemic blood (poor in oxygen) and pumping it to the lungs, while the atrium and left ventricle are responsible for receiving blood from the lungs (rich in oxygen) and pumping it throughout the body.

- Valves

Photo retrieved from d-scholarship.pitt.edu

The heart has four one-way valves that allow blood flow in one direction and prevent blood from returning when pressures change, these are:

- The semilunar valves (aortic and pulmonary)

- The atrioventricular valves (mitral and tricuspid)

Diagram of heart valves (Source: Modified from OpenStax College via Wikimedia Commons)

Atrioventricular valves allow blood to pass from the atria to the ventricles during diastole (relaxation of the ventricles) and prevent blood flow in the opposite direction during systole (contraction of the ventricles).

Sigmoid valves, on the other hand, allow the flow of blood from the ventricles to the arteries (aorta and pulmonary) during systole, and prevent the flow in the opposite direction, that is, the passage of blood from the arteries to the ventricles during diastole.

Both types of valves are composed of sheets of flexible and resistant fibrous tissue that is lined with endothelium. Their movements are rather passive and it is their orientation that allows the unidirectionality of the blood flow.

The two groups of valves work in sequence, that is, when one opens the other closes and vice versa.

Semilunar or sigmoid valves

There are two semilunar or sigmoid valves: one aortic and one pulmonary. The aortic valve is located between the left ventricle and the aorta artery, meanwhile the pulmonary valve is located between the right ventricle and the pulmonary artery.

The aortic semilunar valve prevents the return of blood from the left ventricle, while the pulmonary semilunar valve performs the same function, but prevents the backward movement of blood from the right ventricle to the pulmonary artery.

This pair of valves closes when the ventricles are in the resting or diastole phase, that is, when they are filled with blood from the atria.

Atrioventricular valves

These valves perform a similar function to the semilunar valves, but are located at the connection sites between the atria and the ventricles. There are also two atrioventricular valves, but their names are the mitral valve and the tricuspid valve.

The mitral or bicuspid valve has two leaflets and is located between the left ventricle and the left atrium; This valve prevents blood flow from the ventricle to the atrium when the former contracts.

The tricuspid valve has three leaflets and is located between the right ventricle and the right atrium. Its function is to prevent the reverse flow of blood from the ventricle to the atrium when the right ventricle contracts.

The tricuspid and mitral valves are closed when the ventricles are in systole or contraction phase, that is, when the ventricles empty through the pulmonary and aortic arteries.

- Partitions

The septa are sheets of fibrous tissue that separate the cardiac chambers. There is the interatrial septum (which separates both atria) and the interventricular septum (which separates both ventricles).

The main function of these "walls" is to prevent mixing of blood between the left and right chambers.

- Nodules or nodes

The heart has a system of electrical self-excitation that spontaneously triggers the heartbeat (contractions) with a certain rhythm and frequency.

The cells responsible for this automatism are located in a structure called the sinus node or sinoatrial node, which acts as the heart's natural pacemaker and is located in the upper part of the right atrium, near the mouth of the vena cava.

The excitation that originates in this node is conducted from there, in a spatio-temporal coordinated manner, first towards the atrial muscle and reaches another node located in the lower part of the interatrial septum, near the junction between atrium and ventricle.

This node is called the atrioventricular node. It has the capacity for automatism, as well as the sinus node, but more reduced, although in some cases where the sinus node fails, it can take on the role of a pacemaker.

The atrioventricular node also slows electrical conduction to the ventricle, allowing the atria to contract before the ventricles.

- Fascicles

Fascicles are specialized pathways for conducting arousal. In the atria, there are three bundles called internodal bundles, which conduct excitation from the sinoatrial node to the atrioventricular node.

The fibers that make up the bundle or bundle of His originate in the atrioventricular node, which conducts excitation from the atrium to the ventricle.

On the right side, the upper part of the interventricular septum, the right and left branches of the bundle of His are divided. The left branch crosses the septum and descends on the left (internal) side of the septum.

In the lower part of this septum, the branches of the bundle of His branch to form a system of fibers that conduct excitation towards the ventricular muscle, this system is known as Purkinje fibers.

Connected arteries and veins

The heart chambers and blood vessels are connected in two different circuits. One of them is known as the systemic circuit and is the one that starts in the left ventricle, which drives oxygenated blood to the aorta.

This blood continues to all the arteries of the body, circulates through all the capillaries, where it delivers oxygen to the tissues, is collected in all the veins and venules of the body and then returns to the heart through the vena cavae, which lead to the atrium right.

From there, the deoxygenated blood passes into the right ventricle, where the second circuit or pulmonary circuit begins. This blood leaves the trunk of the pulmonary artery and is distributed through the right and left pulmonary arteries towards the pulmonary capillaries, where it is oxygenated.

It is then collected by the pulmonary veins and transported to the left atrium, where the systemic circuit is repeated again.

Vasculature of the heart

The nutritional and oxygen needs of the heart muscle do not come from the blood contained in the heart chambers.

Instead, the heart has a dedicated vascular system, through which it receives blood that contains all the elements necessary for its function and survival.

This system is the coronary system, which originates at the base of the aorta artery, just after the aortic valve. It is formed by the right and left coronary arteries, which branch and are distributed throughout the myocardial tissue.

The return blood is finally collected by the venous sinus and cardiac veins that flow into the cardiac chambers.

References

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