Single and double circulation

Single circulation is a type of circulation where the blood only passes through the heart once. This type of circulation is found in most fish and amphibians. Double circulation is a type of circulation where the blood passes through the heart twice. This type of circulation is found in most mammals, birds, and reptiles. In double circulation, the blood is first pumped from the heart to the lungs, where it is oxygenated, and then back to the heart before being pumped to the rest of the body. This helps ensure that the body’s cells and organs receive the oxygen and nutrients they need.