The heart doesn't have to do as much work to pump blood when in orbit. After only one day beyond Earth's gravity, astronauts have a lower blood volume. They can lose as much as 20 percent of their blood volume while on a space mission. Since the body has less blood to push around and the heart is pushing more blood with each beat, an astronaut's heart rate also slows down to compensate. What process is being described? Breathing Excretion Homeostasis Respiration

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