Red Blood Cells in Space

The cardiovascular system and the contained red blood cells are the backbone of oxygen transportation in the human body. From an evolutionary point of view, this system is rather ancient and originated approximately 500 million years ago when multicellular organisms had grown so much that transportation of oxygen and nutrients by diffusion had become insufficient. The development of erythrocytes containing hemoglobin to bind oxygen and carbon dioxide reversibly occurred approximately at the same time and marks an important step in the evolution of more complex forms of life. Today, we know that the production and release of erythrocytes from the bone marrow in humans is regulated by a hormone called erythropoietin. In adults, the kidneys are the organ responsible for the production and release of this hormone. Specifically, erythropoietin is stimulating erythropoiesis by increasing the proliferation, differentiation, and maturation of the erythroid precursors. Most remarkably, already during early spaceflight in the 1960s and 1970s, it was realized that blood volume, red blood cells, and haemoglobin concentrations are severely altered in astronauts. This chapter briefly describes the time course, magnitude, and means by which this reduction occurs and what the impact for living and working in space might be.