Regional Blood Flow

Sea turtles can control some aspects of their circulation, an adaptation that allows them to retain heat (Spotila, et al, 1991). A turtle’s flippers are not very well insulated and readily exchange heat with their surroundings over their large surface area (Hochscheid, et al, 2002). By constricting and dilating the blood vessels that lead to the flippers, sea turtles can decrease the amount of heat exchange between the flippers and the core of the body (Hochscheid, et al, 2002).

Diagram 1

When turtles are in warmer temperatures, the blood vessels between the flippers and the body dilate, and blood flow to and from the flippers is elevated. The warm blood is transferred to the core of the body. When turtles are in cooler temperatures, the blood vessels between the flippers and the body constrict, and blood flow to and from the flippers is reduced. The cool blood is not transferred to the core of the body, and very little warm blood is transferred from the core of the body to the flippers, where it would be cooled by the surroundings (Hochscheid, et al, 2002). The fact that live sea turtles warm up at a faster rate than they cool down, whereas dead sea turtles warm up and cool down at the same rate, indicates that turtles have some control over their blood flow (Heath and McGinnis, 1980).

A countercurrent exchange mechanism also plays a part in sea turtle thermoregulatory physiology. A countercurrent exchanger is present when arteries that feed blood from a warm area gradually exchange heat with veins that feed from a cool area, thus maintaining an elevated temperature in the warm area (Diagram 1). In order for heat to be exchanged, the veins and arteries must share surface area. The more shared surface area, the more heat exchanged. Countercurrent exchangers typically consist of a matrix of veins and arteries (Diagram 2) or a larger artery surrounding by smaller veins (Diagram 3).

Diagram 2

Diagram 3

In sea turtles, the warm area is the core of the body, and the cool area is the skin of the flippers. Countercurrent exchangers with a matrix form (Diagram 2) are found in the front and back flippers of leatherbacks (Greer, et al, 1973). Countercurrent exchangers with a radial form (Diagram 3) are found in the front flippers of loggerheads and green turtles (Hochschied, 2002).
Regional blood flow, coupled with countercurrent exchangers, affects the rate at which sea turtles exchange heat with their environment. In warm water, they absorb as much heat as possible by dilating blood vessels to the flippers. When they move from warm water to cool water, they retain the heat they had gained. However, they must have some aspect of endothermy in order to have a constantly elevated body temperature, even after extended periods of time in cold northern waters.

Leatherback, photo courtesy of Matthew Simonds

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This web site was completed by Katie Fitzpatrick in partial fulfillment of the requirements for Dr. Michael Dorcas's Biology 312, Animal Physiology, at Davidson College in Fall Semester 2005.

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Please direct all comments and questions to Katie Fitzpatrick at kafitzpatrick@davidson.edu