Answer:
Birds are animals with a closed, double and complete circulatory system. In the closed circulatory system, the blood of these animals circulates only within vessels; In the dual circulation system, the birds' blood passes twice through the heart; and in the complete circulatory system, arterial blood does not mix with venous blood.
The heart of the birds has four chambers (two atria and two ventricles) that are totally separate. Venous blood (rich in carbon dioxide) from the animal's body is carried to the right atrium through veins; while arterial (oxygen-rich) blood from the lungs reaches the left atrium. Through simultaneous systoles, blood from the two atria is pushed to the respective ventricles (right atrium to the right ventricle; and left atrium to the left ventricle). From each ventricle, blood is driven into the arteries.
The artery that connects to the right ventricle is the pulmonary artery and it is through it that venous blood reaches the lungs, and the artery that is connected to the left ventricle is the aorta, which carries arterial blood to all organs and tissues. from the animal's body.
The circulatory system of birds resembles that of mammals, with slight differences, for example: the red blood cells of the birds are nucleus-shaped and oval-shaped, while the red blood cells in mammals are non-nucleus (anucleated) and round in shape. Another difference is that in birds, the aorta artery that leaves the left ventricle is turned to the right, while in mammals, the aorta artery is to the left.
The fact that the birds have dual and complete circulation gives these animals a greater availability of oxygen and, consequently, a greater availability of energy for the animal to take flight and also to keep its body temperature constant (homeothermy).
In addition, birds tend to have larger hearts than mammals (in terms of body size and mass). The relatively large hearts of birds may be needed to meet the high metabolic demands of flight. Among birds, small birds have relatively larger hearts (again in relation to body mass) than larger birds. Hummingbirds have the largest hearts (relative to body mass) of all birds, probably because hovering takes so much energy.
Avian hearts also tend to pump more blood per unit of time than mammalian hearts. In other words, the cardiac output (amount of blood pumped per minute) for birds is typically higher than for mammals of the same body mass. Cardiac output is influenced by both heart rate (beats per minute) and ejection volume (blood pumped with each beating).
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