Oxygen and essential nutrients that are vital for metabolic processes are transported throughout the body by blood. As most of you know the transportation of blood is made possible by the circulatory system. The circulatory system of turtles in general is fairly simple. The system consists of the heart, veins, arteries and capillaries. Sea turtles unlike humans have a three chambered heart. The heart consists of the left auricle, the right auricle and the ventricle. The ventricle is somewhat separated by a partial septum which helps to minimize the mixing of deoxygenated and oxygenated blood.

Blood Flow
    The process begins when deoxygenated blood flows into the right auricle. The auricle contracts and forces the deoxygenated blood into the ventricle. The ventricle forces the blood into the lungs (for more information on this process go to RESPIRATION) of the turtle where carbon dioxide is extracted and oxygen is added. The blood, which is now oxygenated then enters the left auricle. The left auricle then contracts forcing the blood once again into the ventricle. The ventricle then sends the blood throughout the body.
    The oxygenated blood is carried away from the heart via arteries. As the arteries stretch throughout the sea turtles body they become narrower until they become tiny blood vessels named capillaries. These capillaries are small blood vessels that form an exchange system of vital nutrients between the cells of the body and the blood. The blood which is then deoxygenated is returned to the heart through the turtles veins.

Sea Turtle Adaptations
  
    Of all the species the Leatherbacks have developed the most adaptations. Other species have developed some of the same adaptations but not quite to the same extent. Leatherbacks are thermoregulators and can therefore adapt their circulation capabilities to maintain a stable core body temperature above freezing in extreme temperatures (Greer et al. 1973). This is able partially due to the counter current heat exchange mechanisms they posses. The capillaries and smaller veins and arteries exchange heat back and forth to regulate body temperature in the most vital areas of Leatherbacks. This feature helps nesting mothers to avoid overheating and retains heat for the sea turtles in cold temperatures (Frair et al. 1972).
    Contrary to the Leatherback the seven other species are not as highly developed as thermoregulators, they are considered to be thermoconformers because their body temperature more or less fluctuates with the temperature of their environment. This is the reason that most animals can not maintain normal body functions in colder temperatures, as the environmental temperature decreases so does the metabolic rate of their tissues (thus the rest of their body systems slow as well). Green turtles have been recorded as being extremely vulnerable to temperatures varying from those of tropical and subtropical seas (Penick et al. 1998). Loggerheads have been one of the only other species shown that can successfully live outside of the tropics but the surrounding water still needs to be above twenty degrees Celsius (Poland 2000).
    Sea turtles also posses the ability to regulate their heart rate. During long deep sea dives turtles will slow their heart rate in order to conserve as much oxygen as possible, allowing them to remain submerged for longer periods of time. Blood flow is also shunted away from non vital tissues and organs and is directed towards the heart, brain and nervous system (Frair et al. 1972). Leatherback turtles have been reported to have the ability to slow their heart rate down to the point where almost nine minutes may pass between beats (Southwood et al. 1999). Leatherbacks are also known to have a higher concentration of red blood cells than other species of sea turtles allowing them to become the "champions" at deep sea diving because they can retain more oxygen. The retaining of oxygen will be further discussed in RESPIRATION.
 
 

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