You know that your body is made up of cells. Right? But 37 trillion of them! Who could have guessed? And now that we know, what does it really mean? How many is 37 trillion, anyway? And how did they come up with this number in the first place?
Estimate based on volume, and you get only 15 trillion cells; by weight, you get 70 trillion cells. Unfortunately, nobody has actually counted them all yet. (I wonder why?)
They divided the body into parts and estimated the number of cells in each part, from intestines to knees. This works better because cells are packed more densely in some organs than others. There are 100 billion neuron cells in your brain alone. (Interestingly, these neurons each put out a great number of feelers that link up with, on average, the corresponding feelers from 1,000 other neurons. Altogether, your brain contains a staggering 100 trillion circuits with which to compute your thoughts and feelings.)
The smallest cell in the human body is the sperm; the largest, the egg. The ostrich lays the largest egg of any living bird, weighing up to 3.3 lb and measuring up to 7.0 in × 5.5 in; but the largest cell on the planet is probably the egg of the whale shark, measuring up to 11.8 in × 5.5 in × 3.5 in. That’s one big cell!
But I haven’t even mentioned your microbiome yet. That consists of all the single-celled bacteria, archaea, fungi, and protists that live and make their living on and in your body. The generally accepted figure is that there are ten times more microbes living on and in you than there are of your own human cells in your own human body.
This is possible because a human cell can easily have 1,000 times the volume of a bacterial cell, for example. Again, nobody ever sat down one afternoon and counted them. It’s an estimate.
So that’s 372 trillion critters crawling, swimming, and otherwise making their ways around your body, or just sitting still. Many of them are essrntial to your own health. A few are harmful and any number of them may be neutral, neither harming or hurting you. There are so many and they are so tiny and hard to study that it’ll be a long, long time before all that gets sorted out.
So how many is 372 trillion? It’s 372,000,000,000,000. If they were minutes into the past, no animal or plant life had evolved on earth yet. Your ancestors and mine were teensy, tiny, single-celled creatures not terribly different from an amoeba.
If these 372 trillion microbes were inches, they’d reach more than half-way across the galaxy. Any way you look at it, that’s a lot of bugs! All on you.
Wash your hands before you eat.