Habitat and demands The common octopus has world wide distribution in tropical, subtropical and temperate waters throughout the world. They prefer the floor of relatively shallow, rocky, coastal waters, often no deeper than . In especially warm seasons, the octopus can often be found deeper than usual to escape the warmer layers of water. In moving vertically throughout the water, the octopus is subjected to various pressures and temperatures, which affect the concentration of oxygen available in the water. Primarily, the octopus situates itself in a shelter where a minimal amount of its body is presented to the external water. When it does move, most of the time it is along the ocean or sea floor, in which case the underside of the octopus is still obscured. This crawling increases metabolic demands greatly, requiring they increase their oxygen intake by roughly 2.4 times the amount required for a resting octopus. This increased demand is met by an increase in the
stroke volume of the octopus' heart. The octopus does sometimes swim throughout the water, exposing itself completely. Water moves slowly in one direction over the gills and lamellae, into the mantle cavity and out of the octopus' funnel. The structure of the octopus' gills allows for a high amount of oxygen uptake; up to 65% in water at . In situations where the partial pressure of oxygen in the water is low, diffusion of oxygen into the blood is reduced, Henry's law can explain this phenomenon. The law states that at equilibrium, the partial pressure of oxygen in water will be equal to that in air; but the concentrations will differ due to the differing solubility. This law explains why
O. vulgaris has to alter the amount of water cycled through its mantle cavity as the oxygen concentration in water changes.
Circulation The octopus has three hearts, one main two-chambered heart charged with sending oxygenated blood to the body and two smaller branchial hearts, one next to each set of gills. The circulatory circuit sends oxygenated blood from the gills to the atrium of the systemic heart, then to its ventricle which pumps this blood to the rest of the body. Deoxygenated blood from the body goes to the branchial hearts which pump the blood across the gills to oxygenate it, and then the blood flows back to the systemic atrium for the process to begin again. Three aortae leave the systemic heart, two minor ones (the abdominal aorta and the gonadal aorta) and one major one, the dorsal aorta which services most of the body. The octopus also has large blood sinuses around its gut and behind its eyes that function as reserves in times of physiologic stress. The octopus' heart rate does not change significantly with exercise, though temporary cardiac arrest of the systemic heart can be induced by oxygen debt, almost any sudden stimulus, or mantle pressure during jet propulsion. Its only compensation for exertion is through an increase in stroke volume of up to three times by the systemic heart, which means it suffers an oxygen debt with almost any rapid movement. The octopus is, however, able to control how much oxygen it pulls out of the water with each breath using receptors on its gills, The blood of the octopus is composed of copper-rich hemocyanin, which is less efficient than the iron-rich hemoglobin of vertebrates, thus does not increase oxygen affinity to the same degree. Oxygenated hemocyanin in the arteries binds to , which is then released when the blood in the veins is deoxygenated. The release of into the blood causes it to acidify by forming carbonic acid. The
Bohr effect explains that carbon dioxide concentrations affect the blood pH and the release or intake of oxygen. The Krebs cycle uses the oxygen from the blood to break down glucose in active tissues or muscles and releases carbon dioxide as a waste product, which leads to more oxygen being released. Oxygen released into the tissues or muscles creates deoxygenated blood, which returns to the gills in veins. The two brachial hearts of the octopus pump blood from the veins through the gill capillaries. The newly oxygenated blood drains from the gill capillaries into the systemic heart, where it is then pumped back throughout the body. hearts to pump.
Poiseuille's law explains the rate of flow of the bulk fluid throughout the entire circulatory system through the differences of blood pressure and vascular resistance. Shadwick and Nilsson Shadwick and Nilsson Octopuses have an average minimum salinity requirement of , and that any disturbance introducing significant amounts of fresh water into their environment can prove fatal. In terms of
ions, however, a discrepancy does seem to occur between ionic concentrations found in the seawater and those found within cephalopods. In general, they seem to maintain hypoionic concentrations of sodium, calcium, and chloride in contrast to the salt water. Sulfate and potassium exist in a hypoionic state, as well, with the exception of the excretory systems of cephalopods, where the urine is hyperionic. These ions are free to diffuse, and because they exist in hypoionic concentrations within the organism, they would be moving into the organism from the seawater. The fact that the organism can maintain hypoionic concentrations suggests not only that a form of ionic regulation exists within cephalopods, but also that they also actively excrete certain ions such as potassium and sulfate to maintain
homeostasis. One adaptation that
O. vulgaris has is some direct control over its kidneys. It is able to switch at will between the right or left kidney doing the bulk of the filtration, and can also regulate the filtration rate so that the rate does not increase when the animal's blood pressure goes up due to stress or exercise. Some species of octopuses, including
O. vulgaris, also have a duct that runs from the gonadal space into the branchial pericardium. Wells These changes would occur quite gradually, however, and thus would not require any extreme regulation. The common octopus is a
poikilothermic, eurythermic
ectotherm, meaning that it conforms to the ambient temperature. This implies that no real temperature gradient is seen between the organism and its environment, and the two are quickly equalized. If the octopus swims to a warmer locale, it gains heat from the surrounding water, and if it swims to colder surroundings, it loses heat in a similar fashion.
O. vulgaris can apply behavioral changes to manage wide varieties of environmental temperatures. Respiration rate in octopods is temperature-sensitive – respiration increases with temperature. Its oxygen consumption increases when in water temperatures between , reaches a maximum at , and then begins to drop at . The optimum temperature for metabolism and oxygen consumption is between . Variations in temperature can also induce a change in hemolymph protein levels along oxygen consumption. As temperature increases, protein concentrations increase in order to accommodate the temperature. Also the cooperativity of hemocyanin increases, but the affinity decreases. Conversely, a decrease in temperature results in a decrease in
respiratory pigment cooperativity and increase in affinity. The slight rise in
P50 that occurs with temperature change allows oxygen pressure to remain high in the
capillaries, allowing for elevated diffusion of oxygen into the
mitochondria during periods of high oxygen consumption. The increase in temperature results in higher
enzyme activity, yet the decrease in hemocyanin affinity allows enzyme activity to remain constant and maintain homeostasis. The highest hemolymph protein concentrations are seen at and then drop at temperatures above this.
O. vulgaris does not have any specific organ or structure dedicated to heat production or heat exchange. Like all animals, they produce heat as a result of ordinary metabolic processes such as digestion of food, ==See also ==