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
Branchial heart primary urine in these appendages via pressure filtration. Branchial hearts may have evolved from the pericardial glands of nautiloids, such as those still found in modern nautiluses. Branchial heart Branchial hearts are myogenic accessory pumps found in coleoid cephalopods that supplement the action of the main, systemic heart. Each consists of a single chamber and they are always paired, being located at the base of the gills. They pump blood through the gills via the afferent branchial veins. Since they only circulate venous blood, branchial hearts function under predominantly anaerobic conditions. Branchial hearts also appear to be involved in hemocyanin