The Idea of an Essay, Volume 2

127 is gradual and starts after birth” (p. 526). After the giraffe is born, it experiences a continual growth in blood pressure as its neck becomes longer. Without the increase of hypertrophy of the left ventricle as the giraffe develops, it would not survive because its heart would not be strong enough to pump the blood to the brain. Although the giraffe’s heart is not surprisingly big for its body, the heart is extremely strong and is able to pump the blood to the brain. The hypertension the giraffe needs to supply blood to the brain has the potential to cause multiple problems within the giraffe, however, there are four specific mechanisms that have been designed into its system that prevent these problems. The first of the four mechanisms are the jugular valves. The jugular vein is a large vein that returns blood to the heart from the head. When a giraffe lowers its head to take a drink of water, there is a possibility that blood could enter the jugular vein from the heart because of the high blood pressure. This must be prevented in order to keep the blood from flowing the opposite direction through the jugular vein and to maintain the cardiac output (the amount of blood pumped throughout the giraffe’s body) (Mitchell, Van Sittert & Skinner, 2009). Based on an experiment done by Mitchell, Van Sittert, and Skinner (2009), the jugular valves’ main function was indeed concluded “to direct the large amounts of blood, returning to the heart via the interior vena cava, into the right atrium, and to prevent its flow into the jugular vein” (p. 180). They also concluded that these valves develop during gestation. Giraffes have two jugular veins, right and left (Mitchell, Van Sittert & Skinner, 2009). During this experiment the jugular veins were opened and the number of valves and the position of valves were determined (Mitchell, Van Sittert & Skinner, 2009). It was discovered that the number of valves was of no significance. A long jugular vein could sometimes possess the same number of valves as a short vein (Mitchell, Van Sittert & Skinner, 2009). However, the position of the valves was found to be significant (Mitchell, Van Sittert & Skinner, 2009). According to Mitchell, Van Sittert, and Skinner (2009), while dissecting the jugular veins of twenty five adult giraffes and five fetal giraffes, they found a higher percentage of valves were located at the proximal end, close to the heart, than at the distal end, further from the heart. Four of the giraffes did not contain any valves at the distal segment of the jugular vein. According to Mitchell, Van Sittert, and Skinner