Heart physiology
Organisms that have high metabolic rates need efficient ways to deliver oxygen to cells around their body.
The circulatory system (heart, blood vessels and blood) and the respiratory system (lungs or gills, and other structures involved in the breathing process) are essential for mammals, amphibians, reptiles, and fish to deliver oxygen to respiring tissues.
The main blood vessels involved in the circulation of blood around the body are:
- Arteries – carry blood away from the heart (under high pressure).
- Capillaries – smallest blood vessels which exchange nutrients, gases, and waste products between the blood and the body tissue.
- Veins – carry blood back to the heart (under low pressure).
The heart has two types of chambers – atria and ventricles. Atria are where blood enters the heart and ventricles are where blood leaves the heart.
Birds and mammals have higher metabolic rates than reptiles and amphibians, which in turn have higher metabolic rates than fish.
Mammals and birds
Circulation
Mammals and birds have a complete double circulatory system allowing oxygenated and deoxygenated blood to flow separately from each other within the heart.
Complete double ciruculatory systems allow for higher metabolic rates to be maintained as there is no mixing of oxygenated and deoxygenated blood.
This means that blood leaving the heart to travel to the body is rich in oxygen. This is essential for the high-energy demands of birds and mammals.