When physiology shapes anatomy, lifespan of body parts

While the general features of human beings can be described with pictures and models of body parts in various degrees of assembly, actual human beings exhibit a great deal of variability that is dictated by their physiology. In fact, many of your body parts are a different age than your birth age. The process of self renewal is important for you to understand, because its efficiency changes with age.

Dr. Jonas Frisen at the Karolinska Institute in Stockholm used carbon 14 that was incorporated into DNA during above ground testing of nuclear weapons prior to 1963 to follow the age of DNA in human tissues [published in Cell 2005 Jul15;122(1):133-43]. Carbon 14 is a low intensity radioactive atom that decays slowly with a very long half life.

dividing cells in various stages of mitosis

Mitosis of Living Cells, photomicrograph by Dimarion at Shutterstock.com

Within cells most molecules are constantly being made and destroyed. An exception is the DNA, the genetic material of the cell. A cell acquires its DNA on the day its parent cell divided, and it is kept intact by repair mechanisms until the cell dies. Because DNA does not change over the lifetime of a cell, the extent of carbon 14 enrichment can be used to figure out the age of cells.

There are two ways for a body to produce new cells. The first way, mitosis, is for a particular cell type, such as a liver cell, to divide and produce two new cells that are copies of the original.

The second way is for adult stem cells within tissues to make new replacement cells. There are different types of adult stem cells depending upon where in the body they are located, and depending upon what kind of new cell they produce. Stem cells themselves are present in very low numbers, but once they begin dividing and develop characteristics of the cell type they are replenishing, a single stem cell can produce millions of offspring.

Only a few body parts last most of your lifetime. They are the neurons of the cerebral cortex, the inner lens cells of the eye, and muscle cells of the heart. For more about adult neural stem cells in the central nervous system, the brain and spinal cord, read my posts titled “Birth of New Neurons Continues in Human Brain into 5th Decade” and “Ependymal Cells”.

In contrast the life span of your white blood cells is very short.
physical appearance of human red blood cells, white blood cells, and platelets under a microscope

Human Blood Cells, illustration by Alila Medical Media at Shutterstock.com

Neutophils can survive 3-4 days unless they digest bacteria. Then they die in about 12 hours. Eosinophils live about 3 weeks. Basophils last about 3-10 days. The life span of B lymphocytes that produce antibodies ranges from 4 days to 5 weeks. T lymphocytes can last either a day or two or for months depending upon their battle with foreign substances. Monocytes and platelets interact in many settings such as inflammation and blood clotting and leave the circulation at random. Erythrocytes, red blood cells, live 120 days.

The life span of each type of tissue depends upon the work load endured by its cells. Cells lining the acid filled stomach last only about 5 days. The outer layer of skin is recycled about every two weeks. An adult human liver replaces itself about once every year to year and a half. The entire human skeleton is thought to be replaced every 10 years or so in adults.

The constant recycling of body tissues argues that we should provide our bodies with adequate nutrition, exercise, and rest throughout our lifetime. Damage to self renewal processes leads to severe limitations on life style. Recent theories even suggest that when self renewal processes become damaged or disorganized in a tissue that cancer can be the outcome. There are serious discussions among scientists whether the major player in cancer development is faulty, or lack of, DNA repair and mitosis gone awry, or whether it is adult stem cell tissue replenishment that has gone wide of the mark.

If you like this article you may also be interested in the following posts as well.

Stem Cells: An Evolving Definition

Birth of Neurons Continues in the Human Brain into 5th Decade

Bone Live and Dynamic

Do you have questions?

I hope you will tell me what you think about this article describing the mixture of ages among your body parts. Please put your questions or comments in the box below or send them to me by email at DrReece@MedicalScienceNavigator.com. I read and reply to all comments and email.

If you find this article interesting, share it with your fellow students or send it to your favorite social media site by clicking on one of the buttons below.

Reece-4-S2S14-001Margaret Thompson Reece PhD, physiologist, former Senior Scientist and Laboratory Director at academic medical centers in California, New York and Massachusetts and CSO at Serometrix LLC is now CEO at Reece Biomedical Consulting LLC.

Dr. Reece is passionate about helping students, online and in person, pursue careers in life sciences. Her books “Physiology: Custom-Designed Chemistry” (2012), “Inside the Closed World of the Brain” (2015) and upcoming 30-Day Challenge: Craft Your Plan for Learning Physiology online course manual. Read more at Dr. Reece at amazon.com/author/margaretreece.

Dr. Reece offers a free 30 minute “how-to-get-started” phone conference for students struggling with human anatomy and physiology. Schedule an appointment by email at DrReece@MedicalScienceNavigator.com.


Comments

Physiology of Self Renewal — 41 Comments

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  2. It is amazing how these systems evolved 😉

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      I agree. As a supplement to what is written here, recent evidence suggests that even in some parts of the brain new neurons are matured from stem cells during a person’s life span.

  3. Looking for information to present to my kids…..Relevant stuff….as I teach biology to juniors. Nice article…..I will read it to my kids tomorrow.

  4. Christine on said:

    Do you have information for life span on other organ(s)/cell(s) such as pancreas, heart, lungs, fascia tissue cells, etc. Thanks for the info thus far…please expand it.

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      Christie heart muscle turns over very little if at all. Fascia and collagen will heal if torn but do so very slowly because they have poor access to circulating blood. Lung and pancreas have several cell types and turnover varies. In human brain only the neurons of the hippocampus turnover at an appreciable rate. In animals the neurons of the olfactory bulb also turnover. The astrocyte population of the brain does not seem to turnover. Microglia of the brain does proliferate but only when the brain experiences damage.

  5. Derick Anil on said:

    Oh my friend there is no areas of physiology and anatomy that can be any frustrating. Its only celebrations!!!

    Now each moment is a new birth and new life.

    Therefore we can be celebrating mini birthdays every five days once and mega birthdays every ten years once.

  6. Chujor owate c. on said:

    This is a quality work… Its quite comprehensive, i encourage you to do more in your contributiön to knowledge. Thanks

  7. prerna on said:

    I am interested in meditation and its effect on the body. Could you tell me how does the body remove the dead cell and where does it go?

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      I think you must be asking about dead brain cells because you mentioned meditation. Is that correct? In the brain dead cells are surrounded and engulfed by macrophage-like brain cells called microglia. Once inside the microglia enzymes digest the parts of the dead neuron and individual molecules released by the digestion are reused by the cell for other purposes. In other parts of the body most dead cells are removed by macrophages of the immune system in a process similar to that used by microglia in the brain.

  8. prerna on said:

    Thanks for your reply.Could you please tell me when is the cell considered dead?

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      There are markers that can be seen in fixed tissue with a light microscope that indicate a cell is in a process of dying that is irreversible. They include changes in the morphology of mitochondria and breakdown of the cell’s nucleus. The most obvious dead cells to the eye are skin callouses and at this time of year in New York where I live dry skin flakes.

  9. Kristian Moss on said:

    Would it be possible for some citations for the different life spans of cells?

  10. very informative and useful. Thanks for the article

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      Your welcome. I am working on a new post about this subject. It will be on the site later this Month. I too think this is a very important subject.

  11. pheonix13 on said:

    Neat! I love this kind of thing!

  12. M. Hari Prasad on said:

    Good piece of information.
    Whether self-healing process can be accelerated by meditation on a particular organ.

  13. Cat Bosworth on said:

    Thank you. This information as well as that included in the Q & A is directly linked to my area of interest. I am especially interested in the adrenal glands, their age related degeneration as well as if any sources can help them respond to healing. Also, how often do the cells replace?

  14. Margaret
    This is a wonderful article, concise, and written in a “language” we all understand. I wonder if we could apply the same principle regarding the lifespan of a specialized cell (say prostatic cells) would they be benign or cancerous. How long does a prostatic cell usually live?
    Thanks

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      The differentiated cells that behave like stem cells do not become cancerous. I will look up what I can find on turnover of cells in the prostate.

  15. ISUNLAKIN KOYUM J on said:

    WHAT AN INTERESTING ARTICLE !!!?.TOO CONCISE AND USEFUL.

  16. Justine on said:

    I looked up for info on lifespan of cell from victim of rape point of view. Had an idea today how to get over physical effects of rape, brain and its memory is different story but to know most of my cells are new set helps to think that I have almost new body by now. Thnx, I’ll share this thought with others, I hope it will help them too.

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      Justine, that is a very positive way to think. Thank you for sharing that thought.

  17. Michael John, Lab.Tech.@ United Nations on said:

    Very interesting indeed!!!

  18. Thank you for your commitment. Hope you will bring more & more new information about life.

  19. Debasish Majumder on said:

    Great post. hugely beneficial. thank you very much for sharing the post madam.

  20. Sheethal on said:

    What actually determines the life span of each cell is still not clear to me !

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      Embryonic cells have all of their gene programs available for use. As an embryo develops into a fetus, various cell types appear when parts of the total program are turned off and other parts of the program are enhanced in their expression. Life span of a particular cell type is determined by the protein/DNA activity within its nucleus, by what type of proteins that activity produces and how hostile an environment the cell experiences.

  21. Why do neurons and muscles cells have longer life span than any other cell in our body? What specifically causes this and why?

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      The cells that turn over more quickly in the body do so because they usually live in a less protected, more hostile environment. Or, in the case of bone they serve as a reservoir for substances, calcium and phosphate, critical to proper function of the body’s major physiologic controllers, the nervous and cardiovascular systems. The electrical activity of the heart and transmission of signals between neurons are highly dependent upon an adequate amount of extracellular calcium. Phosphate is needed for construction of the energy source ATP. When diet does not provide adequate calcium or phosphate bone is broken down to provide it.

  22. Jim Kellner on said:

    In the article above on the Lifespan of cells, you say “Only a few body parts last ‘most’ of your lifetime. They are the neurons of the cerebral cortex, the inner lens cells of the eye, and muscle cells of the heart”. Are there any cells that are believed to live a persons entire life without reproduction? Also, as far as the neuronal chemicals that hold the code of memory, are they permanent once encoded or are they reproduced (re-remembered) when accessed? Very interesting article and I’m sure I’ll enjoy the other referenced work.

    • Margaret Reece, PhDMargaret Reece, PhD on said:

      For humans there is little evidence of new neuron formation outside the areas involved in memory formation and recall. Memories are not permanent. Each time a memory, or a fragment of a memory is recalled it is updated with newly acquired information. This is why eyewitness testimony is so unreliable.

  23. atiskumar on said:

    It is really a very good article and forward discussion.

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