Plural of atrium; the two upper chambers of the heart that receive blood, or large open courtyards in buildings.
From Latin atrium meaning 'hall' or 'central court of a house.' In anatomy, applied to the heart chambers in the 1600s because of their chamber-like appearance.
The heart's atria are like the lobby of a building—blood enters there first before being pumped out, and this two-chamber design lets the heart work more efficiently than if it were all one big room.
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