Friday, May 8, 2015

Around they go...

Have you ever heard it said that we replace all our cells every 10 years? I have heard variations on this theme for years – and it just isn’t accurate.  Its true that we constantly take in fresh atoms in the food we eat and the air we breath, and of course we lose atoms minute by minute as waste products are given off…but the story of the life span of different tissue types shows that  the life span of cells vary a great deal
blood cells - stained - the purple cells are white cells

Here are some examples
            *  Red blood cells live only about 100 days…as they get warn and inefficient they are removed from the blood stream. New red cells are continually formed in the bone marrow.
          *  Fat cells are replaced at the rate of about 10% per year in adults. The same fat molecules are stored In fresh new cells as needed.
          *   Heart muscle cells are replaced very slowly.  When you are 25, about 1% a year are replaced.  The rate is much less as you get older.
         *  The cells of your cerebral cortex ( brain ) are never replaced – they are repaired but not replaced…   Same with the cells of your spinal cord – that’s why if the spinal cord is severered it can replace the injured nerve cells.
Mesentery - such as blood vessels,body organs
In addition – there is the entire issue of the  growth of the organism.  We all start as one fertilized zygote – there is rapid growth in both the number of cells but also differentiation of cells into specific tissues and organs – the rate of addition of new cells in phenominal in young children and then we settle down in adult hood to maintenance or replacement of cells…

Muscle Cells
You are not the same person that woke up this morning – millions of cells are replaced each minute.  Cell birth and death is a continuous process.  The Smithsonian Institute says that we have 37.2 trillion cells (estimates vary depending on the age and size of person).  The body has evolved to make sure that different cell types can perform their functions efficiently, replacing some rapidly, maintaining others for the long term


I like to remind myself that  the atoms we ingest are not created new for me or destroyed when I use them.   They were all here at the time of the astronomical  “big bang” – then buried in the soil, dissolved in seawater, and involved in the continuous cycle of growth of the organisms.  Atoms  are passed from air and soil to organisms and animals in predictable pathways.  For example - CO2 in the air  can be taken in by corn plants – I eat the corn – I release CO2 and solid waste back into the system where it cycles again – No atoms created – none destroyed.

The Bible speaks of humans passing from dust to dust... it is more accurate to say that our atoms pass from one living organism to other living organisms.

Skin and hair follicles
The foods I eat come from all over the entire world – beef from the hills of California, sardines from the North Pacific – sea weed from Japan in my Sushi – Sugar from beets grown in Idaho – Peanut butter (peanuts grown in East Africa – apples and tomatoes from my back yard.  And for a time these atoms become part of me – but only for a time – before they rejoin the great swirling exchange of atoms in this universe.  Interesting to imagine that I still retain atoms in my body from every meal I have ever eaten – when I was a child, my meals at home and in travels to foreign lands...  still there…

Adipose cells - "Fat"
I like to remember that some of the very same atoms currently in the muscles of these fingers which which I am typing these words have spent part of their history in the muscles and organs of dinosaurs – in giant condors – in earthworms – in jellyfish - in past humans - in giant sequoias and prairie flowers. And when I’m through with these atoms they will be passed on through countless more organisms that  haven’t yet even evolved.

nerve cells

Suppose that radioactive isotopes are given off by a nuclear reaction and suppose that I ingest those radioactive atoms (such as Carbon – 14 or Iodine – 131)  These two can be incorporated into tissue where they can have an ionizing effect within the cell.  Some radioactive isotopes break down fairly rapidly – but others can remain for years – even a lifetime – and  - radioactivity in the cells of the human body continue to cause their damage.  Our bodies can repair a certain amount of radioactively induced damage – but if you need a reason to oppose nuclear testing or nuclear bomb explosiions – here it is.  Some of the radioactive waste from Chernoble  is still circulating in the atmosphere and has been ingested by every air breathing organism, continuing to do damage to human cells...

Smooth epithelial cells

So there you got it – While many cells are replaced – built of new stuff from the foods we eat… and many cells are retained a life time – but with repairs and adjustments as needed.  What a collection of cells we are... enjoy your cells - all of them.