Red-Eared Slider ‒ Anatomy

Turtles have a closed, double circulatory system with a three-chambered heart composed of two atria and one ventricle. Unlike most reptiles, where the sinus venosus functions as a separate chamber, in turtles (Testudines) it exists as a patch of cells that functions similarly to a pacemaker. Deoxygenated blood enters the ventricle from the right atrium and is pumped to the lungs, where it becomes oxygenated and then returns to the heart, a process known as pulmonary circulation. Once back in the heart, the oxygenated blood is pumped to the rest of the body in what is called systemic circulation. Due to their rigid bony shells, turtles cannot expand their chests to inhale. Instead, they rely on the contraction of flank muscles near their limbs to enlarge their body cavity, enabling inhalation. Exhalation occurs when other muscles contract, pushing the viscera upward and compressing the lungs. Turtles have short, asymmetrical kidneys located in the caudodorsal (near the back of the tail) region. In females, the kidneys are in contact with the oviduct, while in males, they are adjacent to the testes.