Blood

Cells in plasma

How does the blood work?

About 5 liters in an adult. Red cells carry oxygen, white cells defend, platelets clot, and plasma carries everything else.

Red blood cells

Packed with hemoglobin — an iron-containing protein that binds oxygen in the lungs and releases it in tissues. Each cell lives about 120 days.

Making new cells

Bone marrow makes about 2 million red cells per second, which requires iron, vitamin B12 and folate.

Clotting

Vitamin K is needed to activate several clotting proteins.

Evidence & sources

• Red blood cells live about 120 days. Evidence: established. Known: Established through red cell labeling studies. Unknown: — Source: NIH National Heart, Lung, and Blood Institute, Blood basics / anemia resources (Current revision).

Connected topics

• Iron
• Vitamin B12
• Folate (B9)
• Vitamin K
• Bone Tissue
• Kidneys

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.