37.2 Trillion

Yesterday in Sunday School the teacher mentioned that she is a school teacher.  She said she teaches life science to 13-year-olds. One of the commenters decide to use a life science analogy.  He said that he heard that the human body is composed of 7 billion cells.  The teacher quickly corrected him and said there are actually 300 million cells in the human body.  She seemed very sure of herself as if she was quoting fact. Well, this piqued my interest because I thought her estimate was extremely low.  I thought that the man making the comment was closer.  But I wasn't sure. Instinctively it just didn't sound right.  I probably learned that at one point during my biology studies but I don't remember.

So, I decide to look it up.  Come to find out, both estimates were grossly underestimated.  The average human body has 37.2 trillion cells in it.  Of course people come in different sizes so the estimate is 30-40 trillion cells in a human body.

Trillion is a hard number to wrap your mind around.  Lets think of it in terms of $1000 bills.  1 million is 1000 thousand dollar bills. A $1 million stack of $1000 bills would be 4 inches high.  $1 billion is 1000 million dollars. A billion-dollar stack of $1000 bills is 358 feet high.  Around the height of a skyscraper. $1 trillion stack of $1000 bills would be 67.9 miles high!  Think of driving 67.9 miles with $1000 bills lining the road stacked sideways -- not end-to-end.  It would take an hour to drive that far going 67.9 mph.

Another way to try to wrap your head around the vastness of 1 trillion is to think of it in seconds. 1000 seconds is 16 minutes.  1 million seconds is 12 days.  1 billion seconds is 32 years. 1 trillion seconds is 32,000 years.

Now that you have somewhat of a grasp of how much 1 trillion is, let's elaborate on the cells in the human body. So how do you count the number of cells in the human body?  Well, you can't.  But using mathematics ye can come up with a good estimate.

In 2013 a group of European researchers came up with their best estimate for the number of cells in the human body.  The number they came up with was 37.2 trillion.

There are about 200 different types of cells in the human body.  There are different sizes and composition of human cells. The researchers who came up with the number 37.2 trillion used the five most common types of cells in the human body which account for 97% of cell types in our bodies.  They did the calculation of a 100 kg (220 pound) adult male.  This is how they came up with the 37.2 trillion number.

Interestingly red blood cells make up over 80% of our body in terms of cell numbers.  20 to 30 trillion red blood cells.  Yet they total only 4% of total body mass.  You can put 100 red blood cells side by side and they would equal approximately the diameter of a human hair. Contrast that with fat cells.  Fat cells make up only about 0.2% of the total number of cells in our body.  Yet they total around 19% of our body mass. There are around 50 billion fat cells and approximately 2 billion heart muscle cells in our body.  But they pale in comparison to the 20 to 30 trillion red blood cells in our bodies.

There is no way to really know how many cells make up your body.  If you calculate the weight or mass of an average human cell and compare that to the average mass or weight of the human body you get 70 trillion cells.

If you calculate the average volume of the human cell and compare it to the average volume of a human body you get 15 trillion cells.  That's a huge difference!  So the 30 to 40 trillion sounds logical.

Interestingly, it is estimated that there are 10 times more bacterial cells in and on our bodies than human cells which make up our bodies.  But they are so much smaller that they only account for around 200 g body weight.  Which is less than half a pound.

Anyway, that was a long way of making my point that the Sunday School teacher/life science teacher was exceedingly low (as I suspected) in her estimate of the number of cells in the human body. In terms of scale using our time analogy.  300 million seconds = 9.8 years.  37.2 trillion seconds equals 1,190,400 years.  9.8 years versus nearly 1.2 million years is a huge difference!  Vast discrepancy.

People need to get their facts straight before they go around lying to everyone.

That's my two cents.

References:

https://www.wonderopolis.org/wonder/how-many-cells-are-in-the-human-body

https://www.medicalnewstoday.com/articles/318342#Human-and-bacterial-cells