What type of circulation involves blood passing through the heart only once in each complete circuit of the body?

Single circulation refers to a type of circulatory system in which blood passes through the heart only once for each complete circuit around the body. This system is typically found in fish and some amphibians, where the blood flows in a single loop from the heart to the gills (or lungs in the case of some amphibians) for oxygenation and then directly to the rest of the body.

In single circulation, deoxygenated blood returns to the heart and is then pumped out again without any additional passage through the heart during the oxygenation process. This means that the heart acts as a pump for the entire circuit in one go, effectively managing the flow of blood to and from the body's tissues in a straightforward manner.

In contrast, pulmonary circulation involves blood traveling between the heart and lungs specifically for oxygenation, and then returning to the heart before being sent out to the rest of the body (characteristic of double circulation). Double circulation, therefore, includes two separate loops—one for oxygenation and one for systemic circulation. Open circulation refers to a different system altogether where blood is not always contained within vessels and can mix with body fluids, typically seen in some invertebrates.