In the course of evolution, the blood system became more complex. From the moment the heart appears, the number of its chambers increases, and the vessels departing from it differentiate. A heart with three chambers gives organisms a number of advantages over a simpler organ. Animals have a higher vital energy.
Heart complication
In the lancelet, the anterior abdominal vessel pulsates.
In fish, the heart already consists of one atrium and one ventricle.
Who has a three-chambered heart? In amphibians, the atrium has two parts that open into the ventricle with a common opening.
A three-chambered heart is also characteristic of reptiles. Already in lizards, snakes, turtles and crocodiles, each atrium has an independent opening opening in the ventricle. The holes have valves. Reptiles, like amphibians, have the only ventricle, but it is divided by an incomplete septum, which grows from bottom to top.
Birds and animals that feed their babies with milk have two atria and the same number of ventricles. Both atria and ventricles are completely separated from each other.
From the above list it is clear that a three-chambered heart is characteristic of amphibians and reptiles. However, the device still differs not only in the classes of these animals, but also between genera. So, in crocodiles, the septum between the back of the heart is almost complete. Despite this fact, crocodiles remain cold-blooded animals, because blood containing a large percentage of carbon dioxide enters the main arterial trunk. Mixed blood flows through the vessels going to the body.
Outgrowths in the ventricle of the heart as the beginning of septum formation
Those with a three-chambered heart have small and large circles of blood circulation. This improves the overall standard of living. Moreover, who has a three-chambered heart, the ventricle has a tendency to form outgrowths. The frog already has numerous protrusions, which significantly divides the arterial blood and the one in which there is a high content of carbon dioxide. However, tadpoles have a single blood circulation.
The structure of the three-chamber heart of a frog
Amphibians have a heart with three chambers.
The ventricle has thick walls. The atria communicate with the ventricle through a common opening. The right atrium is larger in volume. It receives blood from the whole body, which has given up the element of oxidation. Blood flows from the lungs to the left half of the heart. The venous sinus is associated with the right atrium. He pumps blood to the heart. On the right side is the arterial cone. It is also found in lower fish. Includes a number of valves. Serves for pumping blood into blood vessels. In amphibians, the cone is divided by a partition into two sections.
Blood flow pattern in the frog heart
Blood with a high content of carbon dioxide mixed with saturated oxygen goes to the right atrium, and only enriched with an element for oxidation to the left. The atria contract at the same time. Blood passes into a single ventricle. Here, outgrowths interfere with strong mixing of the blood. The arterial cone departs to the right of the ventricle, so blood containing more carbon dioxide first flows here. It fills the cutaneous-pulmonary arteries. There is a spiral valve in the cone. With increasing blood pressure, it shifts, opening the opening of the aortic arches. Mixed blood from the middle part of the ventricle rushes here. Further, the blood pressure rises even more, and the spiral valve opens the mouth of the carotid arteries that go to the head. Blood flows into the carotid arteries, as the remaining vessels are already full.
Circulatory system of lizards and other reptiles
In lizards and snakes, two circles of blood circulation are not completely separated. But the degree of their separation is higher than that of amphibians. Two aortic arches are preserved. There is a wall in the ventricle, but it does not completely divide the heart chamber into two halves. Crocodiles are believed to have four chambers in their hearts. Although the opening between the ventricles is still preserved.
Thus, vertebrates with a three-chambered heart have greater mobility compared to fish. They can go to land, where they feel great. Vital activity has evolved.
Individuals with a three- and four-chambered heart always have two circles of blood circulation, which also greatly increases the mobility of organisms. And for land vertebrates, this is necessary in conditions when the body is much harder to keep than in the aquatic environment. In the presence of two circles of blood circulation, the blood carrying oxygen goes under sufficient pressure, as it again passes through the heart. And it does not mix with venous.
Some frogs leave their shelters in early spring, when the snow has not yet melted. One of the first to appear in the middle lane is grass frogs.
Those with a three-chambered heart have greater mobility in cold conditions than other cold-blooded representatives.