One Second in Your Body

We think and live in slow terms. The chemical reactions that power us work in very fast terms. One second is fairly short for us, yet so much happens in that time, nerve signalling, heart beating, muscle contractions, and millions and trillions of chemical reactions. So here’s a short overview of some of what happens in your body in a single second.


  • 5 million of your cells will die. But don’t panic, they’re being replaced at exactly the same rate! And 2 million of those dying and being replaced are red blood cells.
  • You’ll probably shed about 700 dead skin cells, contributing to all that lovely dust in your house!
  • Collectively you’ll grow 0.5mm of total hair … that’s adding up the minuscule amount each hair strand grows every second!
  • You use about 100 joules of energy.

In your heart

  • Your heart pumps generally once per second, sending about 70mL of blood into the aorta to head around your body.
  • To do this, your heart has first pumped blood from the 2 atria (filling up chamber) into the 2 ventricles (pumping chambers) all in this one second.
  • That means electrical signals have raced all around your heart and synchronised millions of cardiac muscle cells to simultaneously release calcium in order to cause the biochemical reactions of muscle contraction.
  • Throughout your body, all the arteries (carrying blood away from the heart) are rhythmically contracting their muscular layer to continue a little bit of pumping action.
  • In the capillaries (nutrient exchange sites), oxygen is being “offloaded” from the blood cells and carbon dioxide is being “collected” and other nutrients and wastes exchanged.
  • 0.3% of your blood will be filtered by your kidneys, coming up to 20% per minute!

Nervous system

  • Every single neuron, those for processing in your brain as well as the sensory ones, will fire (send a message) roughly 10-50 times every second!
  • That’s a total of over 20 billion messages sent per second!
  • Some sensory neurons can “send messages” at up to 100-150 metres per second in order to rapidly respond to sensory information (like say, touching something hot). However, pain neurons fire far slower at about 1 metre per second, explaining partially why we will often pull away from the hot thing before realising that it’s painful.
  • 10 million bits of information are relayed from your eyes to your brain!


And best for last, with about 37 trillion cells in your body and a rough estimate of 1 billion chemical reactions per cell per second … you have at least 37 * 10^21 chemical reactions occurring every second in your body which is  37 thousand billion billion!


I hope this post merely illustrates a tiny fragment of the absolute incredibility of our bodies! So much more than this happens in a second and no-one can even hope to ever completely quantify that!





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