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The blood that enters the right auricle of the heart comes from the bloodstream. The right auricle is also known as the right atrial appendage. It is a small cone shaped structure from the upper portion of the atrium overlapping the aorta.
Blood that goes into the right atrium comes from  different parts of the body, it is then low or poor in oxygen because cells of different  body tissues has extracted and utilized oxygen carried by the blood