Vertebrates have different body structures. Everyone has a common building plan. This proves descent from the same ancestor. However, the complexity of the body structure varies. It is believed that the complication of the structure went in the course of evolution. That is, more primitive organisms appeared first.
Evolutionary development of organisms
The course of evolution of vertebrates began with the lancelet.
This organism already has a notochord and a neural tube. And also the most primitive heart for vertebrates: the pulsating abdominal vessel.
Further complication of the organization led to the formation of fish. Gill-breathing organisms have a two-chambered heart and one circulation.
Amphibians and most reptiles have a three-chambered heart. This further increases their vitality.
Birds and mammals are at the pinnacle of evolution. The heart is made up of four chambers. There are no openings between the atria, as well as between the ventricles. Two circles of circulationblood is completely separated. Therefore, birds and mammals have warm-bloodedness, which sharply distinguishes them from other animals. Of course, humans also belong to this group.
Three-chambered heart
In amphibians and reptiles, the heart has three chambers: two atria and one ventricle. Scientists have found out that this particular structure of the muscular organ is suitable for the life of these animals.
The presence of two circles of blood circulation provides a fairly high level of vital activity. Animals with a three-chambered heart live on land, they are quite mobile (especially reptiles). They can tolerate a slight drop in temperature without falling into a stupor. Tritons, for example, are the first to emerge from winter shelters when the snow has not yet melted. Spring also wakes up grass frogs very early. These amphibians hop through the snow in search of a breeding partner.
The presence of a three-chambered heart allows amphibians to fall into a stupor when frost sets in. The circulatory system allows not to spend a lot of energy for pumping blood, which would be observed in the presence of a heart with four chambers and a complete separation of the two circulations of blood.
Heart of reptiles
Reptiles have a three-chambered heart with an incomplete septum. It can be seen that their mobility increases dramatically compared to amphibians. Agile lizards are actually very mobile. They are quite difficult to catch, especially in warm weather. However, body temperature is still dependent on the environment. Reptiles are cold-blooded organisms.
Crocodiles have an unusual heart structure. Scientists classify crocodiles as animals with a four-chambered heart. The septum between the right and left ventricles has a large area. However, there is a hole in this wall. Therefore, crocodiles remain cold-blooded creatures. Blood saturated with an oxidizing element mixes with oxygen-poor blood. In addition, the special structure of the crocodile blood system is expressed in the presence of the left artery. It departs from the right ventricle along with the pulmonary. The left artery carries blood to the crocodile's stomach. This structure contributes to faster digestion of food. This is necessary as the reptile swallows large chunks of meat that can start to rot if left in the digestive tract for a long time.
Four-chambered heart
A heart with four chambers has birds and animals that feed their young with milk. These are the most highly organized organisms. Birds are capable of long flight, while mammals are capable of fast running. All of them have warm blood. They remain active even in cold weather, which cold-blooded representatives cannot afford.
Only those organisms that cannot provide themselves with food in winter hibernate. A bear that has not gained enough weight in autumn wakes up and wanders through the snow in search of food.
Thus, the four-chambered heart maximized the vital activity of organisms. Warm-blooded animals are notfall into a state of stupor. Their motor activity does not depend on the ambient temperature. Such vertebrates feel great on land in conditions of strong gravity.
Animals with a three-chambered heart have already acquired two circles of blood circulation. However, the large and small circles are not completely separated. Blood rich in the element of oxidation mixes with blood rich in carbon dioxide. Despite this, the three-chambered heart provides life for organisms on land.
