In an open system, blood flows freely in body cavities, while in a closed system, it is confined to vessels—a far more efficient design for large, active bodies. A giraffe needs immense pressure, khoob, to pump blood against gravity up that long neck to its brain. I teach this, yet I find my answer in my areca trees: their tall, slender trunks need a tremendous, hidden force to lift water to the highest leaves, just as the giraffe’s heart must. My own aching knees remind me daily of the strain a system endures to overcome simple distance.
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