Over the last weekend, I was sorting through my things and realized that I had some tickets to the Museum of Science’s Mugar Omni Theater in Boston, MA that were expiring at the end of the year. So of course I had to go to the museum to see a surround sound, surround screen film. I went to the theater planning to watch a film about the Rocky Mountain Railroad Express. I walked up to the ticket window and saw that the showing times had changed since I’d looked them up online. So instead of exploring the Rocky Mountain wilderness and learning about the history of the railway, I found myself examining the human body. Even though this film is intended for a grade school audience, I walked away with a few new discoveries about the human body and new perspective on my own body.
So in honor of all those New Year’s resolutions to change yourself for the better, I present the new you, already different today than yesterday:
Your body generates approximately 25 x 10^10 new red blood cells every day, to replace those that naturally die after about 120 days, 200,000 trips around the body, and 300 miles traveled. That’s equivalent to about 2 million red blood cells dying and being created every second.
Every night while you sleep, within your eye, a new layer of cells is growing. And every morning when you first open your eyes, and see the first light, the old layer is burned away revealing a new fresh layer below, ready to take on the day.
Skin cells develop inside the body and slowly push their way up to the surface, by pushing their predecessors off (reminds me of that coin game at arcades, put in one quarter, cause a chain reaction of falling coins, and win tickets!). After only 2 or 3 weeks, a new skin cell has pushed its way to the surface, died, and fallen off your body to join the rest (guess what's in your house dust...). By the end of the year, you will have shed about 8 lbs of skin.
Now let’s do a little math: Red blood cells account for 25% of all cells in the body and live for approximately 4 months. Skin cells live 2-3 weeks and skin accounts for 16% of your body weight. So if we take some liberties and make the assumption that the weight of skin is due solely to cells (just bear with me), then 16% of all cells in the body are skin cells. That means that 4 months from now over 40% of your cells will cease to exist and be replaced with new cells. Over 40% of you will be new!
Ok, my math is a little rough. Ok, a lot rough, but the basic idea is true. A large proportion of your body’s cells (almost all of them) are regularly replaced, making an ever-changing new you.
Not everything about you is new (which is good because then would it still really be you?):
Brain cells die and are never replaced. At least that was the old common knowledge. More recent research suggests that there is some limited capability for regeneration of brain cells, but it is not yet clear how common this is or when it might occur. There is still much to be learned. On the whole though, the brain you have today is the brain you were born with. Cells may have branched and grown, but they essentially the same cells.
NOTE: The brain is composed of two basic types of cells: neurons and glial cells. Glial cells provide the structure; they grow, die, and are replaced like any other cell. The cells we’re talking about when we say, “brain cells don’t die”, are the neuron cells. These are the ones that form the neural connections and are the real power behind the brain.
The average human heart will beat nonstop for over 70 years. The cells grow and die (about a 20 year cycle), but the organ as a whole just keeps going. Can you imagine doing anything nonstop for that long? Of course our heart beats for as long as we live, so this isn’t so surprising a fact. But it’s just a boggling thought to me. Everything else rests for some period of time. We work for only a certain number of hours a day. We play sport or run for only a few hours at a time. We go to school for a limited number of years. We sleep. We rest our eyes. Our muscles relax. Our brains get a respite from active thinking. But our hearts never stop pumping; never stop the same steady beat; never “mixes it up” from early fetal development till death. Our hearts run uninterrupted, unchanging, for longer than any other organ.
As you’re challenging yourself with a new resolution of self-improvement, best of luck. You can do it. You change all the time.
“The Human Body" Film
A first early report on brain cell regeneration: Brain Cells Regenerate BMJ 1998; 317
For more about brain cells
The Naked Scientists: a good site for answering some of your science questions:
Anatomy Atlas for more advanced interest in human anatomy