Disc-shaped cells packed with hemoglobin. Each lives about 120 days, and you make millions every second.
How it works, step by step
Bone marrow builds new cells using iron, B12 and folate.
Hemoglobin's iron binds oxygen in the lungs.
Cells squeeze through capillaries and release oxygen.
After ~120 days the spleen recycles them.
Anemia
Anemia means too few red cells or too little hemoglobin. Iron, B12 and folate deficiency are common nutritional causes — but there are many others, so testing matters.
Evidence & sources
Red blood cells live for about 120 days. Evidence: established. Known: Foundational physiology. Unknown: — Source: NIH NHLBI, Anemia — What Is Anemia? (Current revision).