Practice question

True fishes or Pisces display circulatory architecture comprising two cardiac chambers, single thin-walled atrium receiving deoxygenated blood from sinus venosus and single thick-walled ventricle pumping to ventral aorta and gills via bulbus arteriosus. Oxygenated blood proceeds via dorsal aorta to systemic tissues in single circuit, no pulmonary bypass, resulting in low systemic blood pressure. This two-chambered heart contrasts with three-chambered design in amphibians and reptiles with double circulation partially mixing, and four-chambered separation in birds, mammals and crocodilians enabling high-pressure systemic supply essential for endothermy.