The animal kingdom features diverse circulatory systems. While humans and most mammals rely on a single, four-chambered heart, some organisms have evolved alternative designs to meet the demands of their environments.
The Octopus: Unraveling the Eight-Heart Myth
A common misconception suggests that the octopus possesses eight hearts, perhaps linked to its eight arms. In reality, an octopus has three hearts. One of these is the systemic heart, responsible for circulating blood to the octopus’s body. The other two are known as branchial hearts, and each is positioned at the base of one of the octopus’s two gills. This three-heart configuration is consistent across all octopus species.
A Blue-Blooded Circulatory System
The three hearts of an octopus coordinate to ensure efficient blood flow. The two branchial hearts pump deoxygenated blood through the gills, where oxygen is absorbed. Once oxygenated, this blood then flows to the systemic heart. The systemic heart propels the oxygen-rich blood throughout the rest of the octopus’s body, supplying its organs, muscles, and arms.
Octopus blood is blue, a direct result of the oxygen-carrying protein it contains. Unlike the iron-based hemoglobin found in human blood, which gives it a red hue, octopus blood utilizes hemocyanin. Hemocyanin is a copper-based protein that binds to oxygen molecules, turning blue when oxygenated. This protein is dissolved directly in the octopus’s blood plasma, rather than being contained within blood cells.
Why This Unique Design? Adaptations for Survival
The specialized circulatory system of the octopus, with its three hearts and hemocyanin-based blood, provides distinct advantages for its aquatic existence. While hemocyanin is less efficient at transporting oxygen than hemoglobin at typical room temperatures, it performs more effectively in cold, low-oxygen, and high-pressure marine environments. This makes it particularly suitable for the deep or chilly waters where many octopuses reside.
The multiple hearts help compensate for hemocyanin’s oxygen-carrying properties by ensuring that blood is efficiently re-pressurized after passing through the gills. This is important because blood pressure drops significantly after gas exchange. The continuous and vigorous pumping action maintains adequate blood flow to support the octopus’s active, predatory lifestyle and its energy-intensive nervous system. This unique design contributes to the octopus’s ability to thrive in diverse marine habitats.