Biconcave disc characteristic red color and transport oxygen from the lungs to the tissues. Mature red blood cells are round and biconcave because they lack a nucleus and unlike other cells, red cells require a small amount of oxygen for its metabolism and most oxygen is freed into the tissues. The absence of nucleus, ribosomes, and mitochondria partly contributes to the red blood cell’s disc-like structure which leaves room for hundreds of millions of hemoglobin molecules found within the cells. Hemoglobin is a red and iron-rich protein that merges with oxygen to carry oxygen from the lungs to the body tissues. Both
Packed red blood cells though it has other names and is commonly just called "negative" or "positive." Unlike the ABO antigens, a recipient will not usually react to the first incompatible transfusion because the adaptive immune system does not immediately recognize it. After an incompatible transfusion the recipient may develop an antibody to the antigen and will react to any further incompatible transfusions. This antibody is important because it is the most frequent cause of hemolytic disease of the newborn. Incompatible red blood cells are sometimes given to recipients who will never become pregnant, such as males or postmenopausal women, as long as they