The amphibian heart has a single, undivided ventricle, two atria, a sinus venosus, and a Conus arteriosus. Their sarcopterygian ancestors had hearts with all of these chambers, but the ventricle was partially divided and probably aided in separating pulmonary and systemic circulatory circuits. Check the following statements that could help us understand why amphibian evolution resulted in the loss of the partial ventricular septum. A .The loss of the ventricular septum probably occurred because blood returning to the heart of amphibians bypasses the ventricle being shunted from the sinus venasus and right atrium directly to the pulmonary artery and lungs.
B. Loss of the partial ventricular septum reflects the fact that blood returning to the heart from the systemic circuit is often highly oxygenated because many amphibians rely on cutaneous and buccal gas exchange, as well as pulmonary gas exchange, much of the time.
C. Mixing of blood from the lungs with blood from the body in the ventricle is not a problem. Loss of the partial ventricular septum is not a problem because the spiral valve keeps systemic and pulmonary blood separate within the ventricle.
D. The Conus arteriosus of the amphibian heart receives blood from the right atrium and passes the blood on to the pulmonary circulation. This keeps oxygenated and nonoxygenated blood separate.
E. The slightly asynchronous contraction of left and right atria help keep systemic and pulmonary circuit blood separated in the ventricle.