What is a Red Blood Cell?

Red blood cells are the most common cell in blood. They carry oxygen around the body, from the heart to the extremities. All of the bodies tissues are dependent upon oxygen from red blood cells – if the flow is cut off, the tissue dies. The scientific name for a red blood cell is “erythrocyte,” meaning “hollow red cell.”


Red blood cells get their red color from hemoglobin, which makes up about 97% of the dry weight of red blood cells, and around 35% of the total weight, including water. Hemoglobin is a metalloprotein, meaning it is a protein that includes iron as one of its constituent atoms. In the context of oxygen distribution, hemoglobin contains multiple chemical “slots” for storing oxygen. This oxygen is obtained from the heart, where red blood cells are replenished with oxygen from the lungs.
The red blood cell is the primary component of the circulatory system, also known as the cardiovascular system. In the circulatory system, channels called arteries hold oxygen-rich blood for distribution to the body, while veins return oxygen-poor blood to the heart for replenishment. The oxygen levels of blood can be examined by looking at its color – oxygen-poor blood is bluish, while oxygen-rich blood is red. When exposed to the open through a cut, blood quickly gets oxygenated by atmospheric oxygen, appearing a bright red.
Red blood cells have a diameter of about 6-8 micrometers (millionths of a meter), similar in size to most cells in the body. They have the appearance of an inner tube, albeit without a hole in the center. Adult humans have 20 – 30 trillion red blood cells in their body, about 5 million per microliter of blood. Other cells found in blood include platelets, which assist in clotting, and white blood cells, which serve as the blood’s sentries against pathogens