The Idea of an Essay, Volume 2

128 (2009), the fact that the jugular valves were found closer to the heart indicated that their primary function was to prevent “regurgitation of interior vena cava and right atrial blood into the jugular vein when the giraffe is in the head down position” (p. 179). As the giraffe lowers its head the valves close, and as the giraffe raises its head, returning to its original position, the valves reopen (Mitchell, Van Sittert & Skinner, 2009). The jugular valves, when closed, must withstand the hydrostatic pressure of the blood in the jugular vein and the pressure of venous blood that has already returned to the heart in order to be effective (Mitchell, Van Sittert & Skinner, 2009). The jugular valves do not develop with growth, but are in place during gestation. According to Mitchell, Van Sitter, and Skinner (2009), while dissecting the fetal giraffes, jugular valves were found to be present during gestation. This means that the valves do not develop as the neck elongates but are established before birth (Mitchell, Van Sittert & Skinner, 2009). If jugular valves were not present near the heart, then upon lowering the head blood from the heart would flow back into the jugular vein. Consequently, too much blood would flow back into the brain and not enough blood would remain in the heart to maintain a sufficient cardiac output. The second mechanism that the giraffe possesses is a unique feature in its leg similar to the G-suit that fighter pilots wear. A G-suit is a specially designed suit that is worn by fighter pilots that places pressure on the legs and lower abdomen in order to keep the blood from pooling into their lower extremities when they begin to experience extreme forces. Giraffes have a built in “G-suit” that prevents leakages, due to hypertension, from capillaries in the giraffe’s legs (Khfahl, 1992). Based on an experiment performed by Ostergaard et al. (2011), the pressure exerted on the legs increases closer to the hoof. This is true because of the force of gravity. The maximum arterial pressure that was measured was 350mmHg (Ostergaard et al., 2011). Since there is an increase in pressure, the arterial lumen (the inside of the artery) knee adjusts by gradually narrowing toward the hoof (Ostergaard et al., 2011). The gradual narrowing of the arterial lumen happens two to four centimeters below the knee (Ostergaard et al., 2011). The picture below shows the site where the tissue can be located, and also displays the tissue which was surgically removed and stained to clearly show the