Tag: transportation - the circulatory system

In the case of four-chambered heart, there are two atria and two ventricles. The type of blood circulation in such type of heart is called as double circulation, including pulmonary and systemic circulation. The blood enters twice through the heart in this cycle, which prevents the deoxygenated and the oxygenated blood from getting mixed and the circulation is maintained properly. 

In fishes (e.g., Scoliodon) the heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to the body parts from where deoxygenated blood is returned to the heart (single circulation).
In amphibians (e.g., Frog) and reptiles, the left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium gets the deoxygenated blood from other body parts. However, they get mixed up in the single ventricle which pumps out mixed blood (incomplete double circulation).
In birds and mammals (e.g., Rabbit), oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation.

The heart of an elephant is myogenic, as all the vertebrates have myogenic hearts. Myogenic contraction refers to a contraction initiated by the myocyte cell itself instead of an outside occurrence or stimulus such as nerve innervation. For most insects, heart contraction is initiated and regulated predominantly by external nerves; thus, insect hearts are neurogenic. In contrast, vertebrates, tunicates, and some molluscs have myogenic hearts. The heart beat is initiated and regulated by specialized groups of muscle cells.

The pathway of the blood in the heart occurs in the following manner:

The amphibian carotid labyrinth is a characteristic maze-like vascular expansion at the bifurcation of the common carotid artery into the internal and external carotid arteries.