If you’ve ever wondered which animal has the most hearts, the answer may surprise you – it’s the octopus! With three hearts and also two hearts in each of its 8 arms, the octopus has a whopping 32 hearts in total. That’s a lot of cardiac power for one animal!
In this article, we’ll take a deep dive into the octopus’ incredible circulatory system. We’ll look at how their 32 hearts work together to pump blood throughout their body, the evolutionary benefits of having so many hearts, and some cool facts about these amazing 8-armed creatures and their multi-chambered hearts.
Anatomy of an Octopus’ Circulatory System
Three Main Hearts
Octopuses have a unique circulatory system that includes three main hearts. The largest heart is known as the systemic heart and pumps oxygenated blood to the entire body through the aorta (Ref. American Museum of Natural History).
There are then two smaller branchial hearts located near each set of gills that pump blood only through the capillaries in the gills. This unusual three-hearted system allows an octopus to circulate oxygen and nutrients efficiently to its organs and extremities.
Two Hearts in Each Arm
In addition to the three main hearts, octopuses have two auxiliary hearts in each of their eight arms. These allow for blood circulation within the arm tissue, which can be over 3 feet long in giant Pacific octopuses (Enteroctopus dofleini).
Without these smaller hearts, blood would not be able to circulate all the way out to the ends of their lengthy arms (Ref. Business Insider). The decentralized circulatory system with multiple hearts is essential for these incredible invertebrates.
Single Circulation System
Interestingly, the octopus circulatory system only has one loop, rather than double circulation in vertebrates. In a single system, blood travels from the hearts through blood vessels to reach organs and tissues before returning directly back to the hearts.
In contrast, a double circulation system in animals like humans involves blood first being pumped to the lungs to become oxygenated before circulating to the rest of the body. Researchers believe the octopus single loop system works well due to the efficient gills and blood with the copper-rich protein hemocyanin that readily binds oxygen.
How the Octopus’ 32 Hearts Work
Systemic Hearts
The octopus has three hearts that pump blood to the rest of its body. These three “systemic” hearts are located at the base of the mantle and pump blood to the octopus’ gills, organs, and tissues (Natural History Museum).
The systemic hearts work similarly to a human heart, receiving deoxygenated blood from the veins, pumping it through the gills to oxygenate it, and then pumping the refreshed blood back out to the body.
These three hearts beat at about 40 beats per minute on average to supply the octopus’ full body with oxygenated blood.
Branchial Hearts
In addition to the three systemic hearts, an octopus also has two “branchial hearts” embedded near each of its gills. That’s a total of nine hearts per gill, for a grand total of 32 hearts! The branchial hearts pump blood through the extensive network of vessels intertwined with the gills (CNN).
This ensures highly efficient extraction of oxygen from the water flowing over the gills. The branching network of vessels also helps regulate blood pressure near the delicate gills. Having two hearts per gill likely provides backup pumping power.
So even if one heart stops beating, blood keeps flowing to that gill.
Coordinated Contractions
All 32 octopus hearts beat asynchronously, meaning they contract at individual rates (ScienceAlert). The systemic hearts maintain a steady 40 beats per minute, while the smaller branchial hearts beat at 35 bpm. The hearts don’t rely on internal pacemakers like human hearts.
Instead, their rhythmic contractions pass via nerve impulses. Chemicals like serotonin and adrenaline also help regulate heart rate. Somehow, without a designated master clock, all these decentralized hearts synchronize blood flow excellently in the far-reaching octopus anatomy!
Evolutionary Advantages of Multiple Hearts
Supply Blood to All Arms
An evolutionary advantage of having multiple hearts is being able to sufficiently supply blood to all arms or limbs. For example, the giant Pacific octopus has three hearts that work together to pump blood throughout its eight arms (Smithsonian Magazine, 2022).
Two hearts pump blood to the octopus’s large gills, while the third heart circulates blood to the rest of the body. This allows oxygen and nutrients to reach even the furthest extremities of the octopus’s long, flexible arms.
Survive Attacks
Multiple hearts also help certain species survive attacks by predators in nature. According to researchers, if one heart in an octopus is damaged, the other two hearts can take over and continue circulating blood to vital organs (Ackerman, 2022).
This built-in backup system improves the chances of surviving an encounter with predators trying to eat them.
Similarly, a cockroach has one main heart plus individual auxiliary hearts near each segment and leg. So even if a predator bites off part of a cockroach, the decentralized hearts may allow it to keep pumping blood and survive (Kapoor, 2017).
Having hearts in different physical locations is protective for species vulnerable to attacks.
Regulate Blood Pressure
In addition, multiple hearts can aid creatures in regulating blood pressure more precisely based on regional requirements. For example, if a giraffe lowers its head to get a drink, gravity would normally pool blood in the head and brain as it bends down.
However, valves and auxiliary hearts along the giraffe’s neck constrict to prevent too much blood from flowing (Mattison, 2022). This helps maintain steady and safe blood pressure in the brain despite the shifting pressures.
Likewise, blood pressures differ between a squid’s organs and active swimming muscles. So squid rely on two parallel hearts to separately optimize blood circulation in each region (Carey, 2017). This allows squid both delicate control over blood movement and extreme athletic feats like escaping predators at speeds over 15 miles per hour!
Interesting Facts About the Octopus’ Hearts
Heartbeat Speed Varies
One fascinating thing about the octopus’ three hearts is that each one beats at its own rhythm. The main heart that pumps blood around the body beats slower when the octopus swims quickly to conserve oxygen, while the two smaller hearts that supply the gills continue pumping at a constant speed.
In fact, an octopus’ heartbeat can vary from as slow as 20 beats per minute when resting up to 220 beats per minute during physical exertions or stress. That’s quite an impressive range!
Blue Blood
Here’s a colorful fact for you – octopuses actually have blue blood! Their blood contains a copper-rich protein called hemocyanin which transports oxygen throughout the body. When hemocyanin binds with oxygen it turns a distinct blue color, unlike the red hemoglobin protein found in human blood.
The blue color helps make oxygen transport more efficient in cold ocean environments. Additionally, blue blood likely helps protect octopuses against microbes and toxins as copper ions have antimicrobial properties.
Short Lifespan
| Species | Lifespan |
|---|---|
| Giant Pacific Octopus | 3-5 years |
| Common Octopus | 1-2 years |
It’s astonishing that for all their astounding abilities, most octopus species lead fleeting lives of just a couple years on average. Females often live even shorter than males, because they eventually stop hunting altogether to brood over eggs.
The longest living species is the Giant Pacific Octopus which survives about 3-5 years. By comparison, many vertebrates of similar size live substantially longer. Still, octopuses certainly manage to pack a lot of adventures into their brief lifespans!
Conclusion
The octopus is truly an incredible creature, with its alien-like appearance and bizarre traits like having 32 beating hearts. Their unique circulatory system with multiple hearts evolved to help them survive and thrive in the ocean’s depths.
The next time you see an octopus exhibit at an aquarium, take a moment to appreciate just how amazing their 32-hearted biology really is!
