Birds and humans are both vertebrates with closed circulatory systems. This means they have a heart that pumps blood to the rest of the body through blood vessels. However, there are some key differences between the bird heart and the human heart.
Anatomy
The most noticeable difference between a bird heart and a human heart is that birds have a 4-chambered heart while humans have a 3-chambered heart. Let’s look at the anatomy in more detail:
Bird Heart
The bird heart has 4 chambers:
- Left atrium – receives oxygenated blood from the lungs
- Right atrium – receives deoxygenated blood from the body
- Left ventricle – pumps oxygenated blood to the body
- Right ventricle – pumps deoxygenated blood to the lungs
The left and right sides of the heart are completely separated to prevent mixing of oxygenated and deoxygenated blood. This allows birds to meet their high metabolic demands for oxygen.
Human Heart
The human heart has 3 chambers:
- Left atrium – receives oxygenated blood from the lungs
- Right atrium – receives deoxygenated blood from the body
- Ventricle – pumps blood to both the body and lungs
The right and left sides of the human heart are not completely separated. Some mixing of oxygenated and deoxygenated blood can occur.
Size
Another major difference is that the bird heart is much larger relative to body size compared to the human heart. On average, a bird’s heart accounts for 15% of its body weight. The human heart accounts for only about 0.5% of total body weight.
The large heart size of birds allows them to meet the metabolic demands of flight. A pigeon’s heart makes up around 10% of its body weight, while a hummingbird’s heart may account for 2.5% of its total weight.
Heart Rate
Birds have a much higher heart rate than humans:
Animal | Heart Rate |
---|---|
Hummingbird | 500-600 beats per minute |
Pigeon | 250-350 beats per minute |
Human | 60-100 beats per minute |
The high heart rate of birds delivers oxygen and nutrients to their tissues quickly. During flight, a bird’s heart rate can increase substantially to meet the intense metabolic demands of flapping its wings.
Blood Pressure
Birds have higher blood pressure than humans to overcome the force of gravity during flight. For example:
- Pigeons have a blood pressure around 130/90 mm Hg
- Humans have a blood pressure around 120/80 mm Hg
The thick-walled left ventricle of the bird heart generates immense force to pump blood around the body at high pressure.
Valves
The valves in the bird heart are thicker and stronger than human heart valves. This prevents backflow of blood when the heart is beating rapidly.
Birds also have complete separation of oxygenated and deoxygenated blood. The valves in the bird heart direct blood to the correct side of the heart. Humans do not have complete separation, which allows some mixing of oxygenated and deoxygenated blood.
Metabolism
Birds have a much higher metabolism than humans. Their hearts must deliver oxygen and energy quickly to meet these high metabolic demands. Some examples of metabolic rates:
Animal | Metabolic Rate |
---|---|
Hummingbird | 50 kcal/day/kg body weight |
Sparrow | 13 kcal/day/kg body weight |
Human | 1.2 kcal/day/kg body weight |
The high surface area, thickness, and contractility of the left ventricular wall allow the bird heart to meet these extreme metabolic requirements.
Electrocardiogram
There are also differences in the electrocardiogram (ECG) between bird and human hearts. In humans, the P wave represents atrial contraction and the QRS complex represents ventricular contraction. The PR interval is the time between atrial and ventricular contraction.
In birds, the P wave is often buried in the QRS complex. Birds do not have a separate PR interval. This is because the electrical impulse spreads rapidly between the atria and ventricles in birds, leading to very fast, near simultaneous contraction.
Evolution
From an evolutionary perspective, the bird heart developed to meet the high oxygen demands of flight. The four-chambered heart with complete separation of oxygenated and deoxygenated blood likely evolved as birds required greater aerobic capacity.
In contrast, the three-chambered human heart evolves for bipedal movement rather than flying. The human cardiovascular system had different evolutionary pressures.
Clinical Significance
The differences between the bird heart and human heart have clinical significance for cardiac treatments. For example:
- Birds may not respond to heart medications designed for humans due to differences in heart anatomy and metabolism.
- Understanding the adaptation of the bird cardiovascular system can provide insight into heart problems in humans.
- Studying the structural adaptations that allow higher stroke volume and cardiac output in birds could lead to new approaches to treating heart failure in humans.
Conclusion
In summary, the key differences between the bird heart and human heart include:
- 4 chambers vs. 3 chambers
- Higher heart rate in birds
- Larger relative heart size in birds
- Complete separation of oxygenated and deoxygenated blood in birds
- Higher blood pressure in birds
- Thicker heart valves in birds
- Higher metabolism in birds
- Different ECG patterns
- Separate evolutionary pressures
These cardiovascular adaptations allow the bird heart to meet the intense metabolic demands of flight. Understanding these differences can provide insight into new approaches for treating heart disease in humans.