Octopuses are peculiar creatures with multiple hearts and aquamarine blood that is rich in copper.
The eight limbs of octopuses make them recognizable. What number of organs does a cephalopod have, though?
According to Kirt Onthank(opens in new browser), an octopus biologist at Walla Walla University in Washington, an octopus actually has three organs. Squid and cuttlefish, who are their nearest cousins, share the same characteristics.
The systemic heart, the biggest heart in octopuses, is situated in the center of the mollusc. It circulates blood with oxygen throughout the body, but not to the lungs. It is the biggest and strongest of the three lungs, according to Onthank.
The branchial hearts, the other two hearts in the octopus, are each connected to one of its two gills, hence the name “gill hearts,” according to Onthank. The function of each branchial heart is to circulate blood through the gill to which it is connected. These organs aren’t particularly big or powerful, Onthank said.
Why then do octopuses require three hearts? The same reason that animals like humans require four heart chambers is to address the issue of poor blood pressure, according to Onthank.
Animals’ systems require adequate blood pressure to efficiently distribute blood throughout them. Low blood pressure patients “can get lightheaded or even pass out if they stand up too quickly or exert themselves,” according to Onthank. This is due to the insufficient blood flow to the brain caused by the low pressure.
Octopus lungs help take in essential oxygen from the sea, and the branchial hearts help circulate oxygen-poor blood through the gills. However, the low pressure at which the oxygen-rich blood leaves the gills is “not good for sending blood to the body,” according to Onthank. In order to pressurize the blood once more and effectively send it to the body, octopuses “have another heart after the gills,” he said.
The same issue affects people. Oxygen-poor blood from the capillaries is pumped into the lungs by the right atrium and right ventricle, the heart’s two right compartments. According to Onthank, the oxygen-rich blood exits the lungs at a low pressure.
Humans, on the other hand, return this oxygen-rich blood to the heart, particularly to the left atrium and left ventricle. The blood is repressurized in these compartments before being sent to the remainder of the body via the arteries.
In other words, while humans and octopuses both have hearts, they go about doing so in very distinct ways. Humans have a heart with multiple chambers, whereas octopuses have numerous hearts.
The three hearts are ultimately performing the same function as your four chamber heart, Onthank said. “Octopuses are an excellent illustration of how a sophisticated, sentient creature could develop in a lineage that is entirely distinct from that of animals. Despite having the same issues, they have found diverse answers.
It’s interesting to note that a 1962 study(opens in new tab) hypothesized that the gigantic Pacific octopus Enteroctopus dofleini’s systemic heart may completely cease “for long periods of time when they are resting, when they don’t need high blood pressure as much,” according to Onthank. The “gill hearts do all the work” instead.
In addition, octopus hearts temporarily cease when they move, and nobody knows why, according to Onthank.
The best answer, in my opinion, is that swimming places such a great deal of pressure on their chests that it is better to just halt them for a short while while swimming than to attempt to pump against that pressure, Onthank said. Octopuses move by shooting water streams out of their limbs.
Onthank compared it to inflating a balloon and letting it go to let it soar around. This places a lot of strain on their bodies, which might make it difficult for their hearts to function effectively. They might choose to temporarily put their emotions on hold rather than resisting that temptation, he continued.
Octopuses typically prefer to move over glide. Swimming for octopuses is actually kind of a disaster, according to Onthank. Swimming interferes with their respiration because they propel themselves forward using the same stream of water that they breathe. It is understandable that they don’t swim much considering that swimming briefly stops their heartbeat and affects their respiration.
Blue, copper-based blood
The fact that the blood of octopuses is blue is another manner in which their circulatory system varies from that of people. This is so because, unlike humans, cephalopods such as octopuses transport oxygen in their blood using a copper-based protein called hemocyanins rather than an iron-based protein called hemoglobin. At ambient temperature, hemocyanins are less efficient than hemoglobin at binding to oxygen. One might then naively assume this might be a reason why the octopus requires three hearts. However, Onthank noted that hemocyanins are more advantageous at sea because they transport more oxygen than hemoglobin in low-oxygen conditions and at low temps.
Additionally, cephalopod hemocyanin is more likely to cling to another oxygen molecule when it attaches to one. According to Onthank, it transports oxygen much more efficiently than most hemocyanins thanks to a characteristic known as cooperativity.
Octopus hemocyanin “is at least a comparable, if not better, oxygen transport pigment than hemoglobin” in the water, according to Onthank. Hemocyanin would probably prevent octopuses from conquering land, if that were a possibility.
