Giraffe have unusually high heart rates for their size, at 150 beats per minute. When the animal lowers its head the blood rushes down fairly unopposed and a rete mirabile in the upper neck, with its large cross sectional area, prevents excess blood flow to the brain. When it raises again, the blood vessels constrict and direct blood into the brain so the animal does not faint. The jugular veins contain several (most commonly seven) valves to prevent blood flowing back into the head from the inferior vena cava and right atrium while the head is lowered. Conversely, the blood vessels
Drug delivery to the brain Drug delivery to the brain Drug delivery to the brain is the process of passing therapeutically active molecules across the blood–brain barrier for the purpose of treating brain maladies. This is a complex process that must take into account the complex anatomy of the brain as well as the restrictions imposed by the special junctions of the blood–brain barrier. The blood–brain barrier is formed by special tight junctions between the epithelial cells that surround the brain tissue. All tissue is separated by this layer of epithelial cells, however only the brain epithelial cells have these tight junctions that do not