BREATHS
0 since the page openedResting rate: 15 a minute. None of them become conscious until someone counts.
WHILE YOU READ THIS
0
heartbeats since you opened this page.
None of them required a conscious effort. Below, an incomplete inventory of a day on which your body works without you.
01Right now
You weren't thinking about any of the figures below. They happen anyway, at this rate, for as long as you breathe.
RED BLOOD CELLS MADE
0 made by marrowMarrow makes 2.4 million a second, day and night. Nearly nine in ten cells produced each day are blood cells.
SKIN CELLS SHED
0 released into the world5,800 a second. Part of the dust on your shelves is, literally, you.
BLOOD PUMPED
0 litres5 litres a minute, at rest. A volume the size of an Olympic pool passes through your heart in about a year.
HAIR GROWN
0 nanometres, on your headYour scalp adds 0.35 mm a day. It is growing right now, beneath this line.
BLINKS
0 since the page opened15 a minute. Each one cuts the picture of the world for a third of a second.
02A lifetime
Drag the slider. The ledger is kept by your body, not by me.
- Heartbeats
- 0
- Breaths
- 0
- Blood pumped
- 0Olympic pools
- Epidermal turnovers
- 0about one every 47 days
- Bone-remodelling cycles
- 0full cycles
- Eyes shut
- 0years, from blinking alone
- Dreaming
- 0years of REM sleep
Assumptions, at rest: 72 beats a minute, 15 breaths a minute, 5 litres of blood a minute; blinking: 15 a minute, a third of a second each, 16 hours awake a day; dreaming: 100 minutes a night. Your body's exact values differ; the order of magnitude is everyone's.
03The billion-beat club
In many mammals, resting pulse and lifespan roughly compensate for each other: the result is on the order of a billion beats. A mouse reaches it in two years, an elephant in seventy. Humans are a clear exception: about three billion.
billions of beats per lifetime · rough estimate: average pulse × average lifespan
04What changes slowly
Renewal has limits. Four tissues run on a different clock:
- THE CORTEX
Many of the cortical neurons you are using to read this sentence are the same ones you had twenty years ago. They renew very slowly.
- THE LENS
The core of the lens through which you see this screen formed before birth. Its proteins are not renewed.
- THE OOCYTES
The ovarian reserve forms before birth and declines afterwards. No postnatal production has been demonstrated clinically.
- HEART MUSCLE
It renews by about 1% a year at age 25 and 0.45% at age 75. Over a normal lifespan, fewer than half of the cardiomyocytes are exchanged.
The egg you came from formed inside your mother's ovary, while she was still a foetus. Part of you is older than your mother.