THE 3 TYPES OF HEARTS OF LIVING BEINGS - ANATOMY AND PHYSIOLOGY - 2025

The types of hearts of living beings can be classified into bicameral, tricameral and with four chambers. When we refer to the anatomy of the various species of the animal kingdom, the heart has become a clear example of evolution.

Simply put, vertebrates possess circulatory systems that have differentiated from each other over time. Although there is still great biodiversity within ecosystems, the types of hearts are essentially three.

Within a general classification, fish exhibit a 2-chamber or bicameral heart, amphibians, reptiles (except the crocodile) and mollusks are distinguished by having 3 chambers, and mammals and birds are the most complex, with a system of 4 cameras. We can also catalog them by their embryonic formation, where the tubular, septate and accessory stand out.

Classification of types of hearts

-Bicameral heart

The blood circulation in fish has a simple and closed circuit. This means that it has only one direction, in which blood flows from the heart to the gills and then to the rest of the organs.

Due to their less complex anatomy, these animals have a precise circulatory system that uses 2 chambers. The one with the greatest muscle mass is designated as the ventricle. The one with less musculature has been called the atrium.

This atrium receives the flow of blood that has low oxygen reserves from the tissues and redirects it to the ventricle. From there it will go to the gills so that it can be oxygenated and distributed throughout the animal's body.

Characteristic organs

In most of these species, four essential elements for their functioning can be distinguished; namely:

• Venous sinus. Through the conduits of Cuvier, he is in charge of collecting the blood to send it to the atrium.
• Atrium. This muscular bag receives venous blood (low in oxygen) and routes it to the ventricle.
• Ventricle. Through contraction, its thick walls send blood to the heart bulb.
• Heart bulb. This is responsible for distributing oxygenated blood to the ventral aortas, the branchial arteries, the dorsal aorta and the rest of the system.

-Tri-chamber heart

At first, when they are in full development, tadpoles have a closed circulation like fish. Once they lose their gills and develop lungs, the system becomes twofold, which implies greater circulation and less circulation.

Due to these characteristics, amphibians have a heart that has 3 chambers that are divided into a ventricle and two atria. This allows the aforementioned circulations, where the most extensive represents the organism and the shortest and incomplete the pulmonary system.

This dual system generates two types of blood: arterial (oxygenated) and venous. The separation of this mixture is carried out by the sigmoid valve, which redirects the flow with oxygen to the main organs and the other to the pulmonary arteries.

The amphibian heart is composed of a venous sinus within the right atrium, 2 atria separated by an endocardial-covered septum, and a fairly muscular ventricle. It also has an arterial bulb with arterial and pulmonary branches.

Reptiles

Like amphibians, this class of animals has a 3-chamber configuration with 2 atria and a ventricle with an incomplete dividing wall. Circulation is double, with a pulmonary and vascular circuit almost completely separated.

Pulmonary circulation is independent and leaves directly from the heart. The systemic circulation uses a pair of arteries leading out of the left ventricle. In this case they are the left aorta and the right aorta.

-Heart with 4 chambers

In evolutionary terms, birds do not have the left aorta, while mammals do. The main difference is that the double blood circulation is completely separated thanks to the interventricular septum that forms 4 cavities.

These chambers are represented by the right and left atria and the right and left ventricles. Venous blood flow circulates on the right side, while arterial blood flows on the opposite side.

The short circulation begins in the right ventricle through the pulmonary artery that carries blood to the lungs. Once hematosis (gas exchange) occurs, flow returns to the left atrium.

The longest general circulation originates from the left ventricle through the aorta, from where it travels throughout the body. It then returns to the left ventricle through the superior and inferior vena cava.

Essential processes

Hearts fulfill functions that are inherent to their design and nature, without which we could not survive. Those that are most important are:

• Automatism. This large muscle works by itself, generating an impulse that regulates the heart rate and that depends on the sinus node.
• Conductivity. The conductive and contraction tissues allow rapid diffusion of the electrical impulse throughout the system. This function varies to help the ventricles and atria work properly.
• Contractibility. Due to its evolutionary development, this organ has an inherent ability to spontaneously contract and expand. This mechanism enables the blood cycle and the corresponding oxygenation of the whole body.
• Excitability. All living beings constantly receive a large amount of stimuli that can alter our organic functions. The heart is one of those few organs that reacts in this way.

Other elements

This type of heart, which is also present in humans, contains three essential layers for its functioning:

• The endocardium. Composed of an endothelium, a basement membrane and connective tissue, it is reinforced with elastic fibers that favor the friction and pounding of blood in the cardiac cavity.
• The myocardium. This central area is made up of cardiac muscle tissue, the changing fibers of which aid contraction movement during blood circulation.
• The pericardium. It represents an outer layer that can also change its texture in different areas of the heart. The fibrous pericardium protects it, secures it to other structures, and prevents it from being flooded with blood.

References

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2. Gil Cano, Ma D. Ayala Florenciano and O. López Albors (no date). Fish heart. Veterinary anatomy, Faculty of Veterinary Medicine, University of Murcia. Web: um.es.
3. Online teacher (2015). Cardiac morphology and physiology. Web: profesorenlinea.cl.
4. Biocuriosities (2016). How many types of heart are there? Web: biocuriosidades.blogdiario.com.
5. Elvira Estrada Flores and María del Carmen Uribe A (2002). High Vertebrate Histology. Autonomous University of Mexico. Web: books.google.com.