* Two Atria: The two upper chambers, the atria, receive blood from the body (right atrium) and lungs (left atrium).
* Two Ventricles: The two lower chambers, the ventricles, pump blood out of the heart. The left ventricle pumps oxygenated blood to the body, and the right ventricle pumps deoxygenated blood to the lungs.
* Complete Separation: The four-chambered heart completely separates the oxygenated and deoxygenated blood circuits. This ensures that only oxygen-rich blood is delivered to the body, allowing for greater efficiency and higher metabolic rates.
Here are the specific advantages of a four-chambered heart:
* Increased Oxygen Delivery: The efficient delivery of oxygenated blood to the body enables birds and mammals to maintain high levels of activity and body temperature.
* Higher Metabolic Rates: The increased oxygen delivery allows for faster metabolism, which is crucial for their active lifestyles and warm-blooded nature.
* Endothermy: The ability to regulate body temperature internally, a key characteristic of birds and mammals, is supported by the efficient delivery of oxygen and nutrients provided by the four-chambered heart.
* Enhanced Endurance: The efficient delivery of oxygenated blood to the muscles allows for sustained activity, allowing birds to fly and mammals to run for longer periods.
In contrast, amphibians and reptiles have a three-chambered heart. This means they have a mixing of oxygenated and deoxygenated blood, which is less efficient for delivering oxygen to the body. This is why they are generally less active than birds and mammals.
Therefore, the four-chambered heart is a key evolutionary adaptation that enabled birds and mammals to develop their unique characteristics and ecological dominance.