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Medical Basic physics question

  1. Jul 7, 2008 #1
    I am a Doctor and i am trying to prove a theory concernicg centripetal movements of epithelial stem cells in the human cornea. However my research is about the pterygium, a degenerative lesion of the cornea. I ve proven to be of parabolic form and i know from literature that corneal stem cells are drawed into the cornea by centripetal forces. I found from the book I "motion of the bodies" in the propositions that a body can move in a parabola by centripetal forces.
    My question is quite simple and basic. I would like to know if there is a fundamental law that states that when a body or particle is entered in a field that certain laws of physics exists, then the body or particle must obay them.
    Thank you very much.
     
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  3. Jul 7, 2008 #2

    DaveC426913

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    Certainly, any matter will obey the laws of physics, the key is that you must demonstrate which laws of physics are responsible for what you're seeing.

    Unfortunately, I think you may be barking up the wrong tree. Centripetal forces are normally considered part of laws of motion - these laws are observed in frictionless environments and involve force acting on objects, the object's mass and the resulting acceleration - and very little else. None of these things will apply in the viscous environment of a bodily fluid with particles of negligible mass, with such tiny forces and with such slow movement rates. You just don't get that kind of physics there.

    The kind of physics that might apply might be more like fluid dynamics and diffusion.
     
  4. Jul 7, 2008 #3
    Thank you for quick answer.. The centripetal movements of corneal epithelial stem cells, which originate from the limbus of the cornea and are held responsible for corneal apithelium regenaration are already being proved by fellow colleageus using particular markers and staining of certain antibodies. Regarding the friction issue in the cornea no fluid is present the way that a physic means. My question is still remaining. Is there some fundamental law of physics that states that when a body inserts in a particular field where some laws of physics exists that the body will have to obay them. Any reference would be value. Any more advise would be of major significance.
     
  5. Jul 7, 2008 #4

    Moonbear

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    Just how fast do you think eyes rotate to have centripetal forces affecting pathology? That truly isn't making any sense at all. Are you sure you're using the correct terminology? Or is it possible someone has given a term to the migration of these stem cells that is unrelated to the usage in physics?

    Edit: I've looked into this quickly. And as far as I can ascertain in a quick skim of the handful of papers I've found referring to this, they are using a term called "centripetal motion" to describe the pattern of migration of the stem cells, and this is completely unrelated to the physical concept of "centripetal force."

    http://www.iovs.org/cgi/reprint/30/9/1962

    I'm going to move this thread to medical sciences.
     
    Last edited: Jul 7, 2008
  6. Jul 7, 2008 #5

    Mapes

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    Welcome to PF, iraklis. You appear to be confused between centripetal motion and centripetal force. Even if cells are observed to migrate with centripetal motion (presumably towards the center of the cornea), that is not an indication of a remote centripetal force acting on them. As others have commented, inertial forces would almost certainly be negligible in the eye.
     
  7. Jul 7, 2008 #6
    Sorry I don't have a reference for you but this is what I remember from school. Yes, if a body is inserted in a field, which is itself a convention designed around particular forces, then that body must obey the laws associated with that field. The effects of these laws may be masked by additional forces, namely being canceled out, but by definition of a law of physics ithey is always conformed to.
    However looking back on the term centripetal force, or acceleration, we were taught that it was a "reactive" force. That is it is not a real force but a fictitious force. Used in conjunction with circular motion about a center, it is the force toward the center. In an example of a ball circling around on a string, there the string provides the centripetal acceleration, or force. This force is reacting to,(or better word created by?) the ball's tendency to travel in a straight line. Yes again, a ball traveling freely in a field created by another central force, this time real:gravity, will take the path of a parabola. Hope that helps a little.
     
  8. Jul 7, 2008 #7
    This is a strange question, you are asking us to reference the fact that matter actually obeys the laws of physics?
     
  9. Jul 7, 2008 #8

    DaveC426913

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    Thank you. That's what I thought.

    I think this "centripetal motion" is a fancy term for lateral motion along a surface.

    "Differentiation of these stem cells is coordinated with centripetal motion along the basal layer."
    https://www.novapublishers.com/catalog/product_info.php?products_id=1556


    Perhaps the idea here is that small movements of the eye will aid in migration, much in the same way that grains of sand are moved by wave motion in the shallows of a lake.
     
    Last edited: Jul 7, 2008
  10. Jul 7, 2008 #9

    Moonbear

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    Here's a book excerpt that puts it in plainer English for those of us just learning about this today. :wink:
    http://books.google.com/books?id=Tp...X&oi=book_result&resnum=5&ct=result#PPA424,M1

    Read the first paragraph of the section entitled "Corneal Epithelial Healing."

    It's a term for the post-mitotic cells migrating from the "limbus," which is peripheral to the cornea and contains the stem cells, inward toward the center of the cornea as a means of replenishing corneal epithelium. So, the term seems to have been borrowed simply to indicate motion toward the center from the periphery.
     
  11. Jul 7, 2008 #10
    I am specializing in Ophthalmology actually and i am aware of the basics concerning the cornea. Still i found this article quite interesting and will be probably helping for my publication. Refering to the XYZ theory by Thoft although it has to do with what i am looking for and is part of my references for my publication, still the pterygium is a pathologic state of conjuctival tissue ,in my opinion, which protrude in the cornea since the barrier made by the limbus is malfunctioning allowing this to happen. The XYZ theory is for normal structure corneas, but still the physiology is well described from this hypothesis.
    The whole idea of my publication is to determine the shape of the human pterygia . I manage to do that with the conic section equation in a six variable equation. The whole idea was to link the shape with the centripetal forces or motion. Still although i run in to the term motion i run into centripetal forces as well regarding the stem cell movement from the limbus. May be is an inaccuracy made by us ophthalmologists.. However i must say that all posts were really helpfull. If any more advise is given in order to understand this centripetal motion better in terms of physics i would be really thankfull. Some references concerning physics in that molecular base would probably help me out to understand better if i am not so eager.. Thanks one more time.
     
    Last edited: Jul 7, 2008
  12. Jul 8, 2008 #11

    Moonbear

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    Not everyone reading along is. I was referrring to myself as much as anyone about trying to learn about this new area.

    If others use centripetal forces, it's probably just sloppy terminology. This is one of those situations where you just have to think about the basic physics concept and how it is applied to realize it makes no sense for the context. Centripetal forces in physics apply to rotational motion, not a body that is remaining still (or relatively fixed as the eye is). Just reading what is described, one can discount the physics concept of centripetal forces and see that it is simply a matter of a term being borrowed but having been given a new definition.

    While molecular interactions of course involve physical concepts, I'm wondering if you would be better served thinking about cell signaling events (i.e., is there some extracellular gradient or cell adhesion molecule that's guiding the direction of migration of the newly formed cells)?

    Or, the other thing I'm wondering as I'm contemplating this new information (new to me), is if there is a similar pattern to shedding of old cells? If all the new cells are migrating from outside in to the center of the cornea, is there an area in the center of the cornea with a lot more dead cells than the rest where they are being "shed" to leave room for the new ones to move in? Or is it not quite that organized?

    Anyway, thanks for bringing some new clinical research issues to the forum. Perhaps you'll be able to provide some information on questions folks have asked about eyes and vision here.
     
  13. Jul 8, 2008 #12
    You are actually the only one who peaked up my thread and provided some good thoughts and i am really thankfull.. I hope i was not misunderstand.
    Concerning the cell signaling effects, new cells would migrate and the mitosis would be up to 5fold quicker in case of a central corneal injury like an erosio. Concerning the old cells of the cornea, the hole corneal epithelium is renewed every 7-10 days, with the new cells migrating from the periphery and the old ones being shed from the centre of the cornea into the lacrimal sac and moved away with tears as a result of apoptosis, in normal mitotic conditions , as the XYZ thoery by Thoft states, and this is how it is organised. In any case the old cells are just shed down to leave space for the new migrating ones, but no centripetal motion is involved there.
    Thank you for clearing up for me the centripetal force motion issue. If i got it right you re of the impression that is bad terminology and what they actually think with centripetal motion is a lateral movement of cells?
    If you have some other idea concerning physics, i will be more than glad to hear. May be even clearing up the centripetal motion issue would be even of greater importance, since i think that this misunderstanding is quite common for us.
    Thank you one more time.
     
  14. Jul 8, 2008 #13

    Moonbear

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    Thanks, that's quite interesting.

    Yes, that's what it sounds like. I think the term is being used because they're talking about cells moving from the outside border toward a central point, but really, that's still a lateral movement, just a very specific direction of lateral movement.

    In physics, centripetal force is that force that pulls (pushes?...the actual physicists can correct me here if there's a convention about whether it's pulling or pushing, but for your purposes and mine, it's probably an unimportant detail) an object inward toward the center of an arc so it stays on a curved path rather than flying off in a straight line. For example, if you have a ball on a string and swing it around in a big circle, the centripetal force is along that string toward the direction of your hand to keep the ball going in a circle. If you suddenly release the string, eliminating that force, the ball flies in a straight line from whatever point you released the string. Is that what you're asking, to understand what that force really is to see why it's not what's meant by centripetal motion of migrating cells?
     
  15. Jul 8, 2008 #14
    QUOTE=Moonbear;1795182]Yes, that's what it sounds like. I think the term is being used because they're talking about cells moving from the outside border toward a central point, but really, that's still a lateral movement, just a very specific direction of lateral movement. [/QUOTE]

    How can be a lateral movement explained in terms of physics? Is there some links that you think that might be helpfull for me to understand that better? Thank you one more time.
     
  16. Jul 11, 2008 #15

    NoTime

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    While I don't know much about your particular topic.

    Cells are quite capable of self powered independent motion.
    One article I read shows that one way this works is by microtubule extension and application of the kinesin family of molecular motors.

    The path of the cells are often guided per Moonbear's suggestion of extracellular gradients. They will travel toward or away from the highest concentration of the signal molecule depending on receptors peculiar to the specific cell.
     
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