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Circulatory System

Heart: The heart of the corvus corax uses a four chambered system which allows it to completely separate the oxygenated blood from the deoxygenated blood in the heart, this is much like the heart of mammals but there are key differences in the heart structure to allow better oxygen uptake and dispersal throughout the circulatory system. One key difference in the corvus corax heart structure is the rightward orientation of the aortic arch which allows it to function as efficiently as the mammalian aortic arch but with less actual mass. Another feature the heart has is the branching of two brachiocephalic vessels off the aorta just at the base of the ascending aortic arch; both these brachiocephalic vessels are quite large and are the same diameter as the aortic arch. Deoxygenated blood is brought into the heart from the two precava veins which meet with the sinus venous and the posterior blood is brought into the postcava before entering the right ventricle. Note that the common raven’s heart like most avian organisms lacks a superior vena cava. On the exterior of the heart the key structures to look at are the left and right atrium, the left and right ventricles, and the apex of the heart is quite muscular on the side of the left ventricle. The final arteries to note are the coronary arteries which actually deliver oxygen and nutrients to the heart itself in order to maintain homeostasis. Note that the corvus corax is homoeothermic so its heart must efficiently pump enough oxygenated blood to the cells in order to sustain its high metabolism and body temperature. As you move into the interior section of the heart you will notice a series of different valves which help to control the directional movement of blood. These key valves include the pulmonary and aortic valves, and the mitral and tricuspid valves. These valves work by closing when the heart contracts so there is no back flow of blood, as the heart relaxes the vessels expand allowing blood to flow back into the chambers. The movement of blood begins when it travels through the tricuspid valve into the right ventricle. Note the small amount of muscle surrounding the right ventricle, this lack of muscle is required so the blood can be passed over the lungs through pulmonary arteries without damaging the lungs from high blood pressure. One huge adaptation the corvus corax has to its advantage is the design of the cross-current flow system, this occurs where several capillary beds cross over the lungs allowing for more oxygen to be diffused across the membrane and into the bloodstream. Next the blood travels back to the left atrium through the pulmonary veins which are reddish in coloration compared to the dark blue or purple color of the rest of the venous system. The blood is pumped into the left atrium through the mitral valve, the left atrium nicknamed the ‘workhorse’ is the most muscular section of the heart, this is because it is the most responsible for maintain blood pressure and pumping the oxygenated blood to the rest of the body. The blood finally leaves the heart muscle from the aortic valve and moves through the arteries to its destination.

Arteries: The major arteries of the corvus corax start with one major artery which quickly starts to branch off into smaller and smaller arteries until finally coming to the capillary beds which slow down the movement of blood by having a large surface area to decrease blood pressure. This is needed to allow the most efficient diffusion possible for the organism. The arteries themselves are made up of many different layers of membrane to allow for the blood to be passed through them at high pressure without rupturing the artery itself. Note that both arteries and veins have these membranes but the arteries muscular membrane portion known Tunica media is much larger is size to tunica media on the veins. The branching of arteries begins with the brachiocephalic artery branching off the ascending aorta. Next the common carotid arteries branch from the brachiocephalic artery and then on to the subclavian arteries which are located under the clavicular region of the body. In the corvus corax there is a key difference when looking at the pectoral arteries of the system, unlike most organisms where the pectoral arteries branch off quite quickly the corvus corax’s pectoral artery remains quite large in size. This feature is to accommodate the enormous supply of oxygenated blood to the pectoral muscles when in flight. As the blood hits the capillaries the venous system begins its work to move the blood through the body back to the heart to be re-oxygenated.

Veins: The venous system of the corvus corax much like other birds is composed of the hepatic portal and renal portal system. One advantageous adaptation they have developed is the ability to bypass the renal system completely when doing hard physical activity; this is done by pushing blood through the large venous valves located at the cross between the renal veins and iliac veins. The hepatic portal system uses valves to push blood up from the capillaries in the intestines through the renal vein to the capillary bed located in the liver. It is here in the liver that excess fats and carbohydrates are stored in reserve to feed the rest of the body. As well the capillary bed helps deliver nutrients to the liver itself before moving the deoxygenated blood into another capillary bed to collect and be sent up the renal vein to the inferior vena cava where it begins the cycle again. Note that only veins have valves to stop the back flow of blood and to allow it to move up the body back to the heart.

References: Proctor, N.S.,Lynch, P.J.(1993). Manual of Ornithology: Avian Structure and Function. Michegan: Yale Univversity. pp. 189-203. ISBN 0-300-07619-3

Cite error: A <ref> tag is missing the closing </ref> (see the help page). Although the Corvus corax can live in many different habitats, the common raven is hyperosmotic to its habitat as it is always in a terrestrial habitat. Living in a terrestrial habitat causes a few problems for the common raven, it constantly must intake water and salts to balance its water/salt content in the blood. Since the terrestrial habitat is hyposmotic in relation to the Corvus corax it does not have to worry about water loss, it uses kidneys to regulate salt content in the blood and usually excretes a very dilute excrement. The common raven is a very experienced hunter and will hunt anything from bird eggs, to frogs, to the common field mouse and even up to a small chicken. When times are tough for hunting the Corvus corax will rely on its keen sense of smell and sight to scavenge for food. The Corvus corax is a master scavenger by trade and has an intake of salt by eating mostly carrion from dead animals though the common raven will easily eat human garbage if available to them.

In the case of most of the populations of Corvus corax which live more in the northern parts of North America, harsh winters can be very advantageous with large death rate of herbivores allowing for easy meals for the raven. In fact food can be so bountiful that the common raven which is usually solitary in nature, only ever living with one partner to actually allow other scavengers such as bald eagles, magpies, crows, and other scavenger to fest with them on a dead pile with little to no competition.[1] The difference in diet between the populations of Corvus corax near the sea compared to the boreal forest is immense; ravens near the more marine based terrestrial habitat prey primarily on gulls eggs and hatchlings as well as supplementing their diet with seaweed; note that the feces of these populations showed huge quantities of seaweed indicating that it was an essential source of nutrition even though it was largely indigestible.[2]

These populations have a much higher intake of salt compared to the populations in the more inland regions and therefore excrete more potent hyperosmotic excrement. 

With a diet with sufficient salt concentrations the Corvus corax rarely is desperate for salt intake, instead it focusses on water intake primarily through the food it eats, but if this is not sufficient it will drink water or consume snow in the winter as required. Overall the Corvus corax does quite well in many different terrestrial environments using the adaptations of not only its kidneys but as well its enormously vast and varying diet to keep its osmotic pressures of its blood in check. The Corvus corax truly is the master of its domain, being not only a great hunter but a master scavenger, this species of bird can seemingly withstand any change in its environment and physiological conditions in order to survive and prosper.Edt. Glen P. Semenchuck, “The Atlas of Breeding birds of Alberta”, Federation of Alberta Naturalists, PO Box 1472, Edmonton AB, T5J 2N5, 1992.</ref>

Behavioral and Physiological Adaptations for Thermo Regulation:

The Corvus corax uses many different adaptations in order to regulate its body temperature in order to keep it within a desired range for survival in different climates. Since the common raven does not migrate when the climate becomes colder it must use keep itself warm through the harsh winter, it does this with the use of plumage and body size to surface area ratio. Since most of the Corvus corax’s body is covered in feathers its main adaptation is that the Corvus corax uses is its plumage as buffer between the bird and its environment; in colder temperatures such as that of the harsh northern winters the Corvus corax will puff up its feathers in order to trap air between its feathers and skin^[3]. Since air has a lower conductance of heat, once the air trapped in the plumage heats up it acts like a coat or bubble of warm air that helps to lower the amount of energy the corvus corax must use to generate enough heat to maintain a certain body temperature. On the other side of the spectrum, the common raven will plead and prune its feathers in times of increased environmental temperatures in order to release any trapped air that may increase its body temperature. Another behavioral adaptation the Corvus corax uses is bathing which not only cleans its feathers of parasites but also cools its body temperature by the blood in its feet cooling from the water it stands in while bathing. The Corvus corax also will use a technique known as gular fluttering which is the relaxation and contraction of its throat muscles which promotes increased rate of evaporative cooling. This need to keep metabolic rate low is key to survival in the Corvus corax because with a smaller body size to surface area ratio there is greater heat loss to the environment and a higher metabolic rate compared to larger organisms.

Another major adaptation the Corvus corax uses is the implementation of a countercurrent flow system of blood through its body; especially in its legs as well as decreasing the surface area of the leg so less heat is lost to the external environment. Since the legs are designed in a way that there is such little surface area where heat radiation can occur, there is very little heat loss through the legs to the surrounding environment. Using the countercurrent system within such a small area such as the legs of the Corvus corax allows for heat from the blood in the arteries travelling down the leg to be reabsorbed by the blood in the veins travelling from the foot up back to the heart of the organism. This causes the foot of the organism to remain quite cold but still keep the core body temperature of the Corvus corax to remain in a stable degree^[4]. This reuptake of heat energy allows the common raven to decrease its metabolism/energy expenditure. Another physiological adaptation the Corvus corax uses is it will induce torpor (will actually decrease its metabolic rate) daily in times of harsh weather, it can do this because over the years the Corvus corax has evolved to have a greater range of its thermoneutral zone. Being able to lower its body temperature closer to that of its surroundings allows the common raven to conserve more energy needed to survive. The final big adaptation the Corvus corax uses is shivering thermogenesis which the rapid random contractions of muscles in order to use up adenosine triphosphate also known as ATP and in turn generate heat.

References: Wolf O. Blair, Walsberg E. Glenn. “The Role of the Plumage in Heat Transfer Processes of Birds”, Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona. pg. 575-584, (2000). King R. James, Walsberg E. Glenn. “The Relationship of the External Surface Area of Birds to Skin Surface Area and Body Mass”, Department of Zoology, Washington State University, Pullman, Washington, pg. 76, 185-189, (1978). http://jeb.biologists.org/content/76/1/185.short