The cardiovascular system of humans vs birds.
Both humans and birds have a closed circulatory system, meaning that blood is contained within vessels and does not freely flow through the body cavity. However, there are some key differences between the cardiovascular systems of humans and birds.
Humans have a four-chambered heart, with two atria and two ventricles, which allows for complete separation of oxygenated and deoxygenated blood. Birds also have a four-chambered heart, but their heart is more efficient and adapted for their high metabolic rates. Birds have a higher heart rate than humans, with some species having heart rates as high as 1,000 beats per minute.
Another key difference is the structure of the blood vessels. Birds have a more efficient respiratory system that allows for a higher oxygen exchange rate. Their lungs are more rigid and efficient, allowing for a greater volume of oxygen to be absorbed into the bloodstream. Birds also have a unique adaptation called air sacs, which help to maintain a constant flow of fresh air through the respiratory system, even during both inhalation and exhalation.
Overall, while both humans and birds have closed circulatory systems, birds have certain adaptations that make their cardiovascular system more efficient for their high metabolic rates and requirements for flight.