There are four separate chambers in our own hearts. Frogs, toads, snakes and lizards have only three. The heart of vertebrates performs the function of pumping the blood of the body throughout the body. Similar in many respects, these organs in different classes of vertebrates have a different number of chambers. What are the structural features of the circulatory system and the frog heart?
Classification
Depending on the number of chambers of the heart, vertebrates can be classified as follows:
- Two-chamber: one atrium and one ventricle (in fish).
- Three-chamber: two atria and one ventricle (in amphibians and reptiles).
- Four-chamber: two atria and two ventricles (in birds and mammals).
Functions
What is a heart and why is it needed? Its most important function is the pumping of blood through the circulatory system. Since this organ is really just a pump and does not have any other functions, one might think that in different animals it looks and functions the same, but this is not so.
Instead, nature creates new forms as animals evolve and change their needs. As a result, there are many hearts in terms of structure. All of them perform the same work, namely, they pump circulating fluid through the circulatory system. Let's look at the different types of vertebral hearts and how they developed.
Bicameral heart
All vertebrates have a closed circulatory system with one central heart. The oldest type is the dual chamber, which some modern fish still have. It is a very muscular organ consisting of one atrium and one ventricle. The atrium is a chamber that receives blood that returns to the heart. The ventricle is the cavity that pumps blood from the heart.
These two departments are separated by one one-way heart valve. The device ensures that blood moves only in one direction, from the ventricle and into the blood vessels, where it makes one loop through the circulatory system. Further, the blood extends to the gills (respiratory organ in fish), which take oxygen from the surrounding water. The oxygen-rich blood then flows through the tissues and finally returns to the heart.
Three-chamber heart
The two-chamber heart served fish well for a very long time. But amphibians evolved and crawled out to land, and significant evolutionary changes took place in their circulatory system. They developed double circulation, and now they have two separate circuits of blood flow.
One chain, called the pulmonary circuit, leads to the respiratory system to create oxygen-containing blood. As a result of double circulation, a three-chamber amphibian heart is formed, consisting of two atria and one ventricle. The second scheme, called the system, transfers oxygenated blood to various tissues of the body.
The frog’s heart structure also suggests three chambers. Blood first passes through the pulmonary chain, where it is oxidized, and then returns to the heart through the left atrium. Further, it enters the left side of the common ventricle, and from there, most of the oxygen-rich blood is pumped through a systematic scheme to distribute oxygen in the tissues before it is returned to the right atrium.
Then, blood flows to the right side of the normal ventricle (before it is pumped back into the pulmonary chain). Since both circuits share the ventricle, there is some mixing of blood rich in oxygen and carbon dioxide. However, it decreases due to the presence of a ridge in the center of the ventricle, which somewhat divides its left and right sides.
Four-chamber heart
After the three-chambered heart developed, the logical next step in evolution was to completely separate the ventricle to two separate chambers. This could ensure that oxygen-rich and carbon-rich blood from the two circuits would not mix. This evolutionary progression between three- and four-chamber hearts can be observed in different species of reptiles.
The heart of amphibians and reptiles is usually three-chambered. Different species have walls of various sizes that partially divide the ventricle. The one exception is some crocodile species that have a complete baffle. They form a four-chamber organ, similar to a similar structure in birds and mammals, including humans.
Different hearts: pulmonary and systemic circulation
Blood contains many elements: from nutrients to waste. One vital substance, oxygen, enters the bloodstream through the gills or lungs. To achieve its effective use, many vertebrates have two separate circles of blood circulation: pulmonary and systemic.
Let's look at the four-chamber human heart. In a small circle, this important organ sends blood to the lungs to take oxygen. Blood appears in the right ventricle. From there, it enters the lungs through the pulmonary arteries. Further, the blood goes through the pulmonary veins and moves into the left atrium. Then the blood enters the left ventricle, where a large circle of blood circulation begins.
Systemic circulation is when the heart distributes oxygen blood throughout the body. The left ventricle pumps blood through the aorta, a massive artery that feeds all parts of the body. As soon as oxygen enters the tissues, blood returns through various veins. The entire venous network leads to the inferior or superior vena cava. These vessels go to the right atrium of the heart. Oxygen-depleted blood returns to the lungs.
By keeping these two circles of circulation separate, the four-chamber heart optimizes the use of oxygen. Only oxygen-rich blood enters the body. Only blood containing carbon dioxide goes to the lungs. Birds and mammals have four chambers. Probably the same structure had dinosaurs. Crocodiles and alligators are similar, but they can turn off the circulation in the lungs when they are under water.
Heart structure
How many heart chambers does a frog have? This dark red colored conical muscle is centered in front of the body cavity between the two lungs. The frog’s heart is three-chambered. It is enclosed in two membranes - the inner epicardium and the outer pericardium. The space between these layers is called the pericardial cavity. It is filled with pericardial fluid, which performs the following functions:
- protects the heart from mechanical damage;
- creates a moist environment;
- keeps the frog's heart in the correct position.
External structure
What is the structural feature of the heart of a lake frog? Outwardly, it looks like a triangular structure of a reddish color. Its front end is wide, and the rear end is somewhat pointed. The front is called the conch, while the back is called the ventricle. The shells are two-chamber: the left and right atria. They are demarcated from the outside by a very weak longitudinal inter-risk recess. The ventricle is single chamber. This is the most important part of the heart. It has a conical shape with thick muscle walls and is clearly separated from the atria by a coronary groove.
Internal structure
What is the internal structure of the frog’s heart? The organ wall consists of three layers:
- external epicardium;
- middle mesocardium;
- internal endocardium.
The inner heart is 3-chamber with two shells and one ventricle, separated by a septum. The right shell is larger than the left, there is a transverse oval hole in it , called the sinuoricular. Through it, blood enters the right shell. The hole is protected by two labial valves, called the blue-auricular valves. They let the blood flow to the right, but prevent the reverse movement of blood.
In the left atrium near the septum there is a small opening of the pulmonary vein, which has no valves. The left conch receives blood from the lungs through the pulmonary veins. The ventricle has a thick muscular and spongy wall with numerous longitudinal gaps, separated from each other by muscular protrusions. Both shells open into one chamber of the ventricle using the auriculo-ventricular opening, which is protected by two pairs of auriculo-ventricular valves. The valves are provided with chords that pull the flaps back to close the hole and thus prevent back flow of blood.
The structure and work of the frog’s heart
The heart of amphibians, like any other animal, is a muscular organ that acts like a pumping station. It is centered in the front of the body. The heart is reddish in color and has a triangular shape with a wide front end. The external and internal structure of the frog is significantly different from the structure of the body of other amphibians, but there is a similarity of some internal organs.
Frogs have a heart: a look at the circulatory system
Have you ever felt the heartbeat or the pulse of a frog? If you look at the scheme of the circulatory system of this amphibian, you can see that its structure is significantly different from ours. Deoxygenated blood is sent to the atrium from various organs of the frog body through blood vessels and veins. It merges from the organs, and thus the process of purification begins. Oxygen blood then comes from the lungs and skin and goes into the left atrium. This is how gas exchange occurs in most amphibians.
Both atria discharge their blood into one ventricle, which is divided into two narrow chambers. Thanks to this system, the mixing of oxygen-containing and deoxygenated blood is reduced. The stomach contracts, sending saturated O 2 blood from the left ventricle. She reaches the head, flowing through the carotid arteries. This is almost pure blood, which the brain receives.
The blood passing through the aortic arches is mixed, but it still has a lot of oxygen. This is enough to supply the rest of the body with what it needs. The internal and external structure of the frog and other amphibians are significantly different from underwater inhabitants such as fish, as well as from terrestrial animals, such as mammals.
Is the work of the heart possible outside the body?
Surprisingly, the frog’s heart will continue to beat, even if it is removed from the body, and this applies not only to amphibians. The reason lies in the organ itself. There is a special conducting system of neuromuscular nodes in which impulse excitation spontaneously occurs, spreading from the atria to the ventricles. This is why the frog’s heart function outside the body continues for some time after it has been removed from the body.