Dark blood, called venous blood, is dark because it has deoxygenated after it has traveled through the body before returning to the heart drained of the oxygen. Blood leaving from the heart, called as arterial blood, is pumped from the lungs into the heart through the pulmonary artery, and it contains a large amount of oxygen for delivery around the body. Arterial blood appears brighter red than deoxygenated venous blood. Blood gets its color from red blood cells called hemoglobin, to which oxygen is attached 97% of the oxygen carried by the blood from lungs is carried by hemoglobin.
Hemoglobin helps remove carbon dioxide from the body. the Color difference between venous blood and arterial blood is known as the arteriovenous oxygen difference. Venous blood is also colder than arterial due to its lower oxygen content and PH. A popular and persistent misconception indicates that deoxygenated blood is blue because the veins may look blue because of the way the light is spread by the epidermis. Human skin may also have a bluish color, known as cyanosis, sometimes as a result of certain medical onditions. However, deoxygenated human blood is never blue.