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
Anterior spinal veins how the system works. One of the few major studies of the venous anatomy was conducted by Armin Thron, which can be seen in his published “Vascular Anatomy of the Spinal Cord” from 1988. Anterior spinal veins Anterior spinal veins (also known as anterior coronal veins and anterior median spinal veins) are veins that receive blood from the anterior spinal cord. There are two major components to venous draining: the intrinsic vessels which drain first, and the pial veins which drain second. Within the intrinsic vessels are a group of veins known as central veins. These are organized into individual