Placental mammals have which type of heart?

Placental mammals have which type of heart?

• A. Three-chambered heart
• B. Four-chambered heart
• C. Five-chambered heart
• D. No heart

Answer: (B)

Placental mammals have a four-chambered heart, with two atria and two ventricles that create a complete separation between the blood that circulates to the lungs and the blood that circulates to the body. Oxygenated blood returns from the lungs into the left atrium, moves to the left ventricle, and is pumped to the body; deoxygenated blood returns to the right atrium, goes to the right ventricle, and is sent to the lungs for re-oxygenation. This full separation prevents mixing of the two blood streams, which supports the high metabolic demands of endothermy and active lifestyles. A three-chambered heart, found in many amphibians and most reptiles, has two atria but only one ventricle, where some mixing of oxygen-rich and oxygen-poor blood occurs, making circulation less efficient for high energy needs. A five-chambered heart doesn’t occur in this context, and having no heart would be incompatible with life. The four-chambered design is a hallmark of birds and mammals, enabling efficient, high-rate circulation.

Placental mammals have a four-chambered heart, with two atria and two ventricles that create a complete separation between the blood that circulates to the lungs and the blood that circulates to the body. Oxygenated blood returns from the lungs into the left atrium, moves to the left ventricle, and is pumped to the body; deoxygenated blood returns to the right atrium, goes to the right ventricle, and is sent to the lungs for re-oxygenation. This full separation prevents mixing of the two blood streams, which supports the high metabolic demands of endothermy and active lifestyles.

A three-chambered heart, found in many amphibians and most reptiles, has two atria but only one ventricle, where some mixing of oxygen-rich and oxygen-poor blood occurs, making circulation less efficient for high energy needs. A five-chambered heart doesn’t occur in this context, and having no heart would be incompatible with life. The four-chambered design is a hallmark of birds and mammals, enabling efficient, high-rate circulation.