Our planet is densely populated by animals of various classes, orders and species. Scientists are studying their structure and the functional significance of individual organs. About how amphibians and reptiles have a heart, read the article.
How did a heart from three chambers turn into a four-chamber?
Vertebrates came to land due to the fact that their pulmonary respiration began to develop rapidly. The circulatory system began to rebuild. Gills breathing fish have one circle of blood circulation, their heart consists of only two chambers. They cannot live on land.
Three- or four-chambered hearts have terrestrial vertebrates. They are distinguished by the presence of two circles of blood circulation. Their permanent habitat is land. An organ with three chambers have amphibians and reptiles. Although some species of reptiles have an incomplete division into four parts. The development of a true four-chamber heart during evolution occurred in parallel in mammals, birds and crocodiles.
Reptiles and amphibians
These two classes of animals have two circles of blood circulation and a heart consisting of three chambers. Only one reptile has a defective, but with four cameras, heart. This is a crocodile. A full-fledged cardiac organ first appeared in primitive mammals. In the future, the heart with such a structure was inherited by the descendants of dinosaurs - birds. It was inherited by modern mammals.
Birds
Four-chambered heart have feathered. Birds are distinguished by complete separation of blood circulation circles: large and small, as in humans, when blood does not mix - arterial and venous. The right and left halves of the organ are completely separated.
Birds have a four-chamber heart, its structure is represented by two atria and the same number of ventricles. Venous blood enters the ventricle through the right atrium. From it there is a discharge of the pulmonary artery, which is divided into the left and right branches. As a result, venous blood appears in the corresponding lung. At this time, blood in the lungs oxidizes and enters the left atrium. Such blood circulation is called its small circle.
A large circle of blood circulation originates from the left ventricle. A single vessel departs from it, which is called the right aortic arch, which immediately at the exit from the heart separates two nameless arteries: the left and right. The aorta itself unfolds in the area of the location of the right bronchus and runs parallel to the spinal column as a spinal aorta. Each nameless artery is divided into the carotid and subclavian. The first goes to the head, and the second is again divided into the chest and shoulder. Large arteries extend from the dorsal aorta. Unpaired are designed to supply blood to the stomach and intestines, and paired - to the hind limbs, organs of the pelvic cavity and muscles of the peritoneal walls.
Birds have a four-chambered heart; it differs in that in birds, the blood flows mainly through large vessels, and only a small part of it enters the renal capillaries. Birds are distinguished by the presence of a large heart with frequent contractions and only pure arterial blood entering the organs. This allowed the birds to be considered warm-blooded animals.
Mammalian circulatory system
Mammals have a four-chamber heart, like humans or birds. Its formation with a complete separation of blood circulation circles is caused by the need to develop such a quality as warm-bloodedness. This is explained as follows: warm-blooded animals experience a constant need for oxygen, which only pure blood of arteries with a large amount of oxygen can satisfy. Only a four-chamber heart is capable of providing it with an organism. And the mixed blood of vertebrates, in which the heart has three chambers, is not able to give the desired body temperature. Therefore, such animals are called cold-blooded.
Due to the presence of complete septa, the blood does not mix. In a large circle of circulation, only arterial blood flows, to which all organs of the mammal are supplied to the necessary extent, which helps to accelerate metabolism. This process helps maintain a constant temperature. Four-chamber hearts have mammals, birds, and other classes of animals that need a constant and stable body temperature. Now the environment does not affect them.
Lizards
In fact, the heart of these reptiles has three chambers with two atria and one ventricle. But the principle of his work makes it possible to assert that the four-chambered heart has lizards. The explanation for this phenomenon is as follows. The venous cavity is filled with oxygen-poor blood, the source of which is the right atrium. Arterial blood enriched with oxygen comes from the opposite atrium.
The pulmonary artery and both arches of the aorta are reported. It would seem that the blood should be completely mixed. But this does not happen, since the presence of a muscle flap in combination with a two-phase contraction of the ventricle and further heart function interfere with blood mixing. It is available, but in very small quantities. Therefore, according to the functional value, the three-chamber heart of lizards is similar to the four-chamber.
Reptiles
The crocodile has a four-chambered heart, although the blood circulation circles are not completely separated by a septum. In a reptile, the organ (heart), which is responsible for supplying the entire body with food through the blood, has a special structure. In addition to the pulmonary artery extending from the ventricle on the right side, there is an additional left. On it, the bulk of the blood enters the digestive system.
Between the two arteries, right and left, the crocodile's heart has a hole. Through it, blood from veins has the ability to enter a large circle of circulation, and vice versa. Scientists have long believed that the heart of a reptile is of a transitional nature along the route to the development of a full heart of four chambers, like in warm-blooded mammals. But this is not so.
Turtles
The system of vessels and hearts in these reptiles is the same as in other reptiles: a heart with three chambers, connected veins and arteries. The content of insufficiently oxidized blood increases when external pressure rises. This can happen when the animal dives or moves quickly. The heart rate decreases, although the concentration of carbon dioxide increases significantly.
The four-chamber heart has turtles, although the organ has only three chambers in physiological structure. The fact is that the turtle’s heart is characterized by an incomplete ventricular septum, around which the blood functions, having different amounts of oxygen.