In this article, I would like to consider how the circulatory system of amphibians differs from that of crustaceans and reptiles (reptiles). Representatives of these classes are very similar in many respects, but differences are still present, and sometimes not small. So, about everything in more detail.
First of all, it should be noted that the circulatory system of amphibians is closed. A bicameral heart has only lungless salamanders; in the rest it has a three-chamber. The circulatory system of amphibians consists of two circles of blood circulation: large and small. The presence of the second circle is associated with the occurrence of pulmonary respiration in these animals. The heart is made up of two atria and a ventricle. Moreover, the blood in the atria is different: in the right - mixed, more venous, and in the left - arterial. The walls inside the ventricle form folds that interfere with the mixing of venous and arterial blood. The arterial cone emerging from the ventricle is equipped with a spiral valve. As for the arteries, the pulmonary skin are responsible for the transfer of venous blood to the skin and lungs; carotid - provide the upper body with arterial blood, mainly the head; and the aortic arches carry mixed blood to the remaining organs. The small (or pulmonary) circle begins precisely with the cutaneous-pulmonary arteries. Then, oxygen-enriched blood is collected in paired pulmonary veins that flow into the left atrium. In the arches of the aorta and carotid arteries, which are located in organs and tissues, a large circle of blood circulation originates. Venous blood, flowing through the paired anterior vena cava and through the unpaired posterior vena cava, appears in the right atrium. Through the anterior vena cava, blood oxidized from the skin also gets here, in connection with this, it is mixed in the right atrium. It is because of the presence and characteristics of mixed blood that amphibians are characterized by a low level of metabolic processes. Their body temperature is changeable and depends on that in the environment. This is one of the cold-blooded animals.
The circulatory system of reptiles is similar to that of amphibians, but still it is more adapted to the terrestrial way of life. In reptiles, the heart consists of two atria that open into the ventricle. The cavity of this part of the heart is divided by an incomplete septum (the exception is only crocodiles). That is why the blood that comes from the atria is partially mixed. The arterial cone in reptiles is completely reduced. Two aortic arches and a pulmonary artery independently begin in the heart ventricle. In its left half, the right aortic arch originates, which transfers arterial blood to the head, as well as to the forelimbs. In the middle part of the ventricle, the left aortic arch begins with mixed blood. The arches are connected in the spinal aorta, and the arteries extending from it carry mixed blood to other organs of the body. Moreover, it is very saturated with oxygen, in contrast to that of amphibians, for example.
Unlike amphibians and reptiles, the circulatory system of crustaceans is open. It can rightly be called the most primitive of all the classes considered. Blood in motion is driven by a heartbeat, which is located next to the gills. As such, blood vessels are present only in higher crustaceans, while in others blood flows freely through the cavities around the internal organs. Often special respiratory pigments are dissolved in it, it is they that help to bind more oxygen.
As we see, the circulatory system of amphibians occupies, as it were, an intermediate position between that of crustaceans and reptiles. Reptiles are most adapted to various living conditions, and the organization of blood supply to their body plays a significant role in this.