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
Effect of spaceflight on the human body enough oxygen to the brain without the astronaut's fainting or becoming dizzy. "Under the effects of the earth's gravity, blood and other body fluids are pulled towards the lower body. When gravity is taken away or reduced during space exploration, the blood tends to collect in the upper body instead, resulting in facial edema and other unwelcome side effects. Upon return to earth, the blood begins to pool in the lower extremities again, resulting in orthostatic hypotension." In 2013 NASA published a study that found changes to the eyes and eyesight of monkeys with spaceflights longer than 6 months. Noted