Which animals have a two-chambered heart? Structure and circulation

To move blood through the tissues of the body requires a kind of pump, the role of which is assigned to the heart muscle. In the simplest living beings, such as worms or chordates, this organ is absent, and the structure of the circulatory system is a closed ring. Fishes have a two-chambered heart that pushes blood through the vessels to all parts of the body, opening them access to oxygen, nutrients, and releasing them from metabolic products, delivering them to the breeding sites.

How the blood circulation developed

The circulatory system is the basis of the life of many living organisms. To be able to perform their tasks, the blood must constantly circulate throughout the body. Stages of development of circulatory systems are clearly traced when considering the cardiovascular structure of fish, amphibians, reptiles and birds.

1. Fish belong to cold-blooded animals with a closed circulatory system. They have a two-chambered heart and one circle of blood circulation.
2. Amphibians and reptiles have two circles of blood circulation, their heart is divided into three chambers. The exception is crocodiles.
3. In birds, humans and many animals, the organ that pumps blood is represented by four chambers, and the circulatory system by two circles.

The heart muscle contracts and disperses the blood through the arteries, which are divided into smaller vessels and fit all parts of the body. After giving oxygen and useful elements, the blood is already returned to the veins, called veins, and is enriched.

How the heart works in fish

An animal with a two-chambered heart is usually referred to as cold-blooded. These are representatives of fish and larvae of amphibians. According to the research of biology scientists who studied the development of the circulatory system, it is clear that the first full-fledged swinging organ was detected in fish. These cold-blooded have a two-chambered heart, represented by the atrium with a valve system and a ventricle. The circulatory system forms one whole circle, which drives the venous blood.

The blood from the pump moves through the capillaries of the gills, where it is saturated with oxygen and fills the vessels. Then comes its distribution in the capillaries, which are in the tissues of the body, and their saturation with oxygen. After that, she goes to the veins without oxygen and on them returns to the heart bag.

Structure

Primitive fish have a two-chambered heart, which is conventionally divided into four segments:

• The first segment is a department called the venous sinus, which is responsible for taking blood that gave oxygen to the body;
• The second segment is represented by the atrium with valves;
• The third segment is called the ventricle;
• The fourth segment is an aortic cone with several valves that pumps blood to the peritoneal aorta.

After the blood has left the heart, it moves through the gills, where it is saturated with oxygen and flows into the spinal aorta, from where it spreads to all the tissues of the body.

In higher order fish, all segments are not on one line, but in the shape of the letter S, where the last two segments are above the first two. This structure is inherent in cartilaginous and cystepered fishes. Bony representatives have a weakly arterial cone, which is usually characterized as part of the aorta, not the heart muscle.

Fish Heart Description

In comparison with land mammals, the heart of the fish is small and weak. Its weight varies from 0.3 to 2.5% of body weight. Because of a weak reduction, the pressure in the vessels is also weakened. Due to such features, fish are able to survive icing in severe winters. At this time, the heart of the fish stops beating, and when thawing the reductions are resumed, and the blood begins to circulate through the body, removing the fish from hibernation.

This work of the circulatory system is connected with the fact that fish lead a horizontal way of life and live in an aquatic environment, so there is no need to push the flow of blood upward and to fight earthly gravity.

Features of hematopoiesis in fish

In the body of fish to produce blood cells are capable of several organs:

• gills;
• The intestinal mucosa;
• Epithelium and cardiac vessels;
• Kidney and spleen;
• Blood from the vessels;
• Lymphoid organs formed by the blood-forming tissues and located under the lid of the cranium.

The fish blood contains red blood cells with a nucleus in the center. To date, the system is known, represented by 14 blood groups.

Who else has a two-chambered heart

With the transition of animals to terrestrial life form and with the formation of their lungs, the muscular heart vessels also changed. The organization of animals became more complicated and the heart from the two-chamber was transformed into three- and four-chamber. The second circle of blood circulation was formed, and the heart muscle began to pump not only venous, but also arterial blood.

As evidence that animals began life out of water, scientists lead the stages of breeding of amphibians whose larvae have a two-chambered heart, and their circulatory system is the same as that of fish.

In adults, a three-chambered heart develops, which is represented by two atria and a ventricle. Amphibians are the first animals to have a second circulatory cycle.

The oxygenated blood from the lungs and skin is accumulated in the left atrium and separated by a septum from mixing with the venous that enters the right atrium.

Answering the question about which animals have a two-chambered heart, it can be safely asserted that in adults this organ was preserved only in fish, and in amphibians - at the stage of the larva.