The Idea of an Essay, Volume 2

130 brain would cause the blood vessels in the brain and eyes to rupture if it were not for the rete mirabile or “marvelous net” (Pittman, 2011). According to Pittman (2011), “When the head is lowered, special shunts in the arteries supplying the head restrict blood flow to the brain, diverting it into a web of vessels” (p. 2). The marvelous net is a series of small blood vessels which form a web-like structure (Pittman, 2011).When the giraffe lowers its head to drink, the arteries direct the blood into special vessels which are elastic and keep the brain protected from an overflow of blood. The network of vessels near the base of the brain expands and allows the blood to enter the brain at a normal (100mmHg) arterial pressure (Pittman, 2011). The next mechanism is a “unique anastomosis [or connection] between the carotid and vertebral arteries” (Goetz, 1995; Lawrence, 1948 as qtd in Mitchell, Skinner, 2009, p. 523). This connection prevents fainting when a giraffe lifts its head (Mitchell, Skinner, 2009; Goetz, 1995; Lawrence, 1948). Mitchell and Skinner (2009) refer to Goetz (1957) by saying, “[the connection] directs carotid artery blood into the cerebral perfusion, and an increase in cerebral perfusion pressure [then results]” (p. 523). As the giraffe lifts its head, blood from the heart travels up the carotid artery which is connected to the blood vessels in the brain. The connection between the arteries then directs the blood to the cerebral perfusion, which is a series of blood vessels in the brain. The pressure of these vessels (cerebral perfusion pressure) then increases, and the blood is quickly restored to the brain (Mitchell & Skinner, 2009). Without the rete marible, as the giraffe lowers its head, the blood vessels in the head and eyes would burst. Similarly, without the special connection between the carotid and vertebral arteries the giraffe would lift its head up and then faint, due to lack of blood flow to the brain. The circulatory system of the giraffe is a truly complex system which demands high blood pressure to provide the brain with a sufficient amount of blood, a specifically structured heart that has enough power to produce this pressure, and four mechanisms that allow the giraffe to function despite its high blood pressure. Now, imagine again, the group of tourists on the exotic African safari. They spot a giraffe lowering its head to get a drink of water. Now, when the giraffe raises its head from the drinking, one can appreciate the complexity of the circulatory system and all of the