Blood is divided into arterial blood and venous blood. Most of the arteries in the human body are located in the deeper part of the body and are not easy to see. The blood flowing in the artery is bright red because it contains more oxygen. Therefore, the blood taken from the distal part of the artery, such as the earlobe or fingertip, or the blood flowing out after skin trauma is often red or bright red. In addition, the blood of patients with mild anemia is also bright red. Veins are generally distributed in superficial parts of the body, such as elbows, backs of hands, thighs and feet, and are blue-purple. The blood flowing in veins is venous blood, which is dull because it contains more carbon dioxide and other metabolites. When doing blood tests, blood is often drawn from the elbow vein, so the blood you see is often dark red or black red, which also shows that your blood contains more red blood cells and hemoglobin. In addition, when the blood is concentrated or the venous blood of patients with cor pulmonale can be dark purple.
It is also possible to see that the blood is dark, similar to venous blood, when taking blood from tip parts such as fingertips. This is because most of them come from one end of the peripheral vein, or the hemoglobin concentration is high, or the blood is concentrated.