How does an octopus stay alive even when its heart stops

Research‍‌‍‍‌‍‌‍‍‌ biologically the octopuses are fascinating because in a way they are the most alien creatures among marine animals. Their physiology is something of a paradox, as they can be very different from vertebrates and at the same time use many of the same principles. Their extraordinary feat to be able to function even during a heart-stopping event made the researchers pose a big open physiological question for the scientists. This madultiphasic recording and analysing team (physiologists, evolutionary biologists) then first to show oxygen regulation is left. This is a big deal for medical research that is interested in this area, too - organ survival under hypoxia.Understanding how an octopus manages circulation without continuous cardiac output is a good example of different biological solutions that have been found by nature at the different evolutionary levels. At the same time, it expands the scientific mind about the resilience of biological life systems at a time when hypoxia, climatic stress and metabolic limits are the key challenges of the marine and biomedical research fields, respectively.The octopus's blood system structure is very different from that of mammals, which is the main reason for much of its exceptional endurance and survival power. It is the three hearts that an octopus possesses, not one heart, which makes it the main anatomical difference. Two so-called branchial hearts are located on the gills and pump blood through the respiratory organs, while the central systemic heart circulates oxygenated blood to the rest of the body.In the moment when the octopus is going for a swim, the systemic heart is most of the time slowing down or stops for a very short time, a condition that would cause immediate suffocation in the majority of animals. However, the branchial hearts keep up their work, thus oxygen uptake at the gills is not interrupted. The job division between them enables blood flow to be alive at any moment, even if a certain component is at a standstill. Although the blood pressure is kept quite low, it is still strong enough to sustain the most vital organs. The design sacrifices the energy that would be produced from long-term endurance for that of effectiveness and energy saving during rest and a short burst of movement, the last being in line with the octopus’s habit of catching prey by surprise and saving it during cardiac interruptions.The most important element that the octopus is conditioned to survive a heart stoppage is its acceptance of hypoxia. A study on Octopus insularis as a marine model for evolutionary developmental biology published in Biology Open revealed that cephalopods mainly take up oxygen by haemocyanin, an oxygen carrier which contains copper and is very efficient at low temperatures as well as in case of reduced oxygen. At the same time, haemocyanin is able to give up oxygen to the tissues more easily, even if the blood flow is weak. This biochemical characteristic is the main reason why cells can carry aerobic metabolism for a much longer time without a new blood supply. Besides that, the paper also shines a light on the developmental and genetic aspects of an overall metabolic flexibility concept that covers different life stages. Although these points are only referred to indirectly in the bigger picture of evolution, they provide a solid basis for the idea that octopus tissues are far from rapid damage during transient cardiac pauses. Instead of a complete shutdown, cellular activities slow down, thus allowing more time till circulations returns and no domino of injuries happens, as is the case in oxygen-deprived vertebrate tissues.Keeping alive the ability of a stopped heart is also ascribed to the octopus's decentralised nervous system. More than 50% of its neurons are located in the arms rather than in the central brain, which is the local control for movement and sensation. In this way, the arms can be active even when the circulation is low. After the main cardiac cessation, the brain activity is still on, but not every area of the brain in concert. The cluster of nerve cells in the arms receives the stimuli, and at the same time, they are the executive of the most basic conduct with very scant central authority; hence, here the command is more communication than governance. This distribution of influence reserves energy for the brain and at the same time lessens the oxygen reception that must be continuous. Muscles can be reactive, and the necessary functions, like holding on to surfaces or changing stance, are still going on. This setup is a terrain change as compared to vertebrates, where a lack of cerebral oxygen very soon brings about unconsciousness. In octopuses, neural resilience goes together with circulatory flexibility, both in response to short blood flow interruptions, forming a coordinated reaction that sustains function.One of the immediate benefits of ceasing to endure a temporary heart stoppage is survival in nature. The expanse of octopus habitat is such that oxygen can be scarce at times, for instance, in reefs, tide pools, or crevices with the scarce water exchange. The ability to change the cardiac function lets them stay hidden for quite a few hours without attracting others’ attention with their constant movement. What is more, the physiological cost of escape rapidity is reduced by this; a short burst of jet propulsion, which naturally interferes with systemic heart function, is thus not a problem in such cases. Looking at it from an evolutionary point of view, this feature is the result of selection for efficiency rather than endurance; animals that could balance oxygen use with behavioural stealth are favoured. As ocean temperatures are going up and oxygen levels are down in many parts of the world, the question of such adaptations is becoming more and more important. The example of octopus physiology is one of the survival strategies that do not solely depend on keeping the circulation going, but on developing systems that can still manage during controlled pauses and rapid ‍‌‍‍‌‍‌‍‍‌recovery.Also Read | Why Ladakh is home to nearly 400 snow leopards and where else to find them in India