BLOOD · ACT 01 · a whole body · 1.85 m

THE LAP — one red cell, once round the body

Follow the bright one. It leaves the left ventricle, rides the aorta over its arch and down the body, takes the left leg's arteries to the top of the foot, crawls through a capillary, and comes back up the veins — slower, darker, three-quarters full — to the right heart, which sends it to the lung to fill up again. At rest a lap averages about a minute: your five litres of blood, moved by a heart pumping about five litres a minute. The clock runs in real time. This cell will do this for about 120 days.

  • SCAN Vessels, heart, lungs and skin: BodyParts3D 4.0, one adult male. The cell's path is traced along the scan's own aorta, iliac, femoral and tibial arteries and its inferior vena cava.
  • DRAWN The scan's veins stop at the pelvis, so the return up the leg is drawn beside the arteries, where the deep veins run. The route through the heart, the lung and the capillary bed is drawn too. Veins are shown darker red: venous blood is dark red, never blue.
  • MODEL A lap averages 5 L ÷ 5 L/min ≈ 1 minute. Time in each part follows the share of blood it holds (most of it is in the veins). One cell in 25 trillion is drawn about 2,000× too big to be seen.
  • MODEL Laps in a life: at a resting minute a lap, 120 days is about 173,000 laps. Everyday activity speeds the circulation, which is how the usual figure of about a quarter of a million comes about.
sources
  • Sender R, Fuchs S, Milo R. Revised estimates for the number of human and bacteria cells in the body. PLoS Biol 2016;14:e1002533 — about 25 trillion red cells (84 % of all human cells by number) in a 70 kg reference man.
  • Shemin D, Rittenberg D. The life span of the human red blood cell. J Biol Chem 1946;166:627–636; Franco RS. Measurement of red cell lifespan and aging. Transfus Med Hemother 2012;39:302–307 — about 115–120 days.
  • Guyton AC, Hall JE. Textbook of Medical Physiology — resting cardiac output about 5 L/min; blood volume about 5 L; distribution of blood volume (systemic veins ~64 %, arteries ~13 %, arterioles and capillaries ~7 %, pulmonary circulation ~9 %, heart ~7 %); arterial and mixed venous saturation.
  • Nadler SB, Hidalgo JU, Bloch T. Prediction of blood volume in normal human adults. Surgery 1962;51:224–232.
  • MedlinePlus (US National Library of Medicine): Complete blood count; RBC count; WBC count; Blood differential; Platelet count; Hematocrit — adult reference ranges.
  • Evans E, Fung YC. Improved measurements of the erythrocyte geometry. Microvasc Res 1972;4:335–347 — diameter 7.82 µm, maximum thickness 2.58 µm, minimum 0.81 µm.
  • Skalak R, Brånemark PI. Deformation of red blood cells in capillaries. Science 1969;164:717–719 — bullet and parachute shapes filmed in living capillaries.
  • Fermi G, Perutz MF, Shaanan B, Fourme R. The crystal structure of human deoxyhaemoglobin at 1.74 Å resolution. J Mol Biol 1984;175:159–174 — PDB 2HHB.
  • Shaanan B. Structure of human oxyhaemoglobin at 2.1 Å resolution. J Mol Biol 1983;171:31–59 — PDB 1HHO.
  • Perutz MF. Stereochemistry of cooperative effects in haemoglobin. Nature 1970;228:726–739 — the iron's move into the haem plane on binding oxygen, and how it is passed on.
  • Severinghaus JW. Simple, accurate equations for human blood O₂ dissociation computations. J Appl Physiol 1979;46:599–602.
  • Higgins JM. Red blood cell population dynamics. Clin Lab Med 2015;35:43–57 — production on the order of 2 million red cells a second.
  • Andrews NC. Disorders of iron metabolism. N Engl J Med 1999;341:1986–1995 — 3–4 g of iron in the body, most of it in haemoglobin; 20–25 mg a day recycled from old red cells by macrophages, 1–2 mg absorbed from food.
  • Hoffbrand AV, Moss PAH. Hoffbrand's Essential Haematology — sites of red marrow in adults; erythropoiesis; platelet lifespan 7–10 days.

Anatomy: BodyParts3D © The Database Center for Life Science (DBCLS), licensed CC BY-SA 2.1 Japan; the derived meshes are re-shared under the same licence. Molecules: RCSB Protein Data Bank entries 2HHB and 1HHO (CC0). The cell's route and the molecule files are built by scripts/extract-blood.py.

EDUCATION ONLY Education only, not medical advice. Reference ranges vary between labs, ages and sexes; a number outside a range on this page does not mean anything is wrong. Questions about your own blood count belong with a doctor.Not medical advice. Lab ranges vary.