How does a cell in the body knows it proper place and function

[Alain De Vos]

E.g. you cut yourself in the finger. The cells seems to know they will become part of your finger.
(No lung tissue will be formed in your finger)

 

[Simon Bridge]

You know how cells reproduce right?
Crudely: A finger cell grows and then halves to make two finger cells.
They know to be finger cells because they are copies of finger cells.

I'll keep the description crude - a biologist will come by soon and fill in the gaps.

The cells that mend the cut in your finger come from your finger - they are already finger cells.
Damage too much of your finger and the cells don't know what they have to be - no finger-cells of the right kind close-enough by to copy easily - healing takes longer, and you get scar tissue forming instead. Scar tissue is the same anywhere in your body - kind-of a default patch.

You do get tissue trying to grow in the wrong place ... but it does not match up with it's surroundings, triggering an immune response. However, there are disorders where tissue grows in the wrong place without getting checked by the immune system... in connection with healing, the most common I think are "adhesion disorders":
http://medical-dictionary.thefreedictionary.com/Adhesions
Adhesions are made up of blood vessels and fibroblasts—connective tissue cells. They form as a normal part of the body's healing process and help to limit the spread of infection. However when adhesions cause the wrong tissues to grow into each other, many different complex inflammatory disorders can arise. Worldwide millions of people suffer pain and dysfunction due to adhesion disease.
... but there are tons of others.

 

[Ryan_m_b]

Tricky question. The simple answer is that it is best to think of cells as cellular automata. Their genomes are essentially if/then databases. Changes in the environment cause changes in gene expression which change behaviour, this change in behaviour causes environmental changes for other cells resulting in changes of expression etc. For more specific answers about what is going in certain circumstances I suggest looking up the processes of wound healing/development you are most interested in.

 

[Andy Resnick]

E.g. you cut yourself in the finger. The cells seems to know they will become part of your finger.
(No lung tissue will be formed in your finger)

This is the $zillion question- if you can figure it out, you will revolutionize medical care (growing replacement parts, for example).

Right now, we distinguish stem cell populations based on what they can do. Embryonic stem cells can become *any* cell, while other stem cell populations (in the bone marrow, in your skin, etc) can only differentiate into a restricted set of cell types. Interestingly, your kidneys have no resident stem cell population and yet normal cell turnover still occurs.

You may be interested to learn about teratomas as well.

 

[Monique]

Well, the answer is quite simple. Every day you make new skin, the cells know to make skin because they're programmed to do so. One can envisage it like a ball rolling down a hill; it can take different paths, but once it has taken a certain path it's difficult or even impossible to take another path. The cells in your finger are already on the right path and thus won't start making lung tissue.

The programming is done by proteins that turn genes on/off. One can deprogram a cell to make a stem cell, by incubating it with different proteins one can steer the way the cell differentiates in. In that way one can make brain cells, heart cells, or liver cells.

The details are far more complicated though..

Tumor cells often loose their program, it's a characteristic to determine the severity of the lesion.

 

[Tzikin]

This is the zillion dollar question. The cellular end of the system of cellular differentiation is partially known but it is the higher control system that tells cells how to differentiate to form the architecture of the body is still a mystery.

The closest that chromosomal DNA can come is to explaining the shape of the body is HOX genes but these only explain the grossest architecture. Generally, the position of the HOX gene on a chromosome decides which part of the embryo the various body parts will grow from. In terms of healing, the lizards that can regrow a tail reactivate the HOX genes but the tail is a very poor replacement for the original. It lacks the original cellular organisation.

The new relatively new specialty of epigenetics which studies the complex proteins around the central DNA ladder could eventually throw light on this mystery since they have far greater memory flexibility and storage than the DNA.

However, until that time, I am left with the explanation that I heard within the oral tradition of medicine created by pragmatic clinicians rather than the academic scientists of medicine. This simply attributes the control of cellular differentiation to the mysterious abstract mind, as if it contains a map of how the body should be and also uses this as an explanation for placebo effects, pain and certain bizarre phantom limb effects that are occasionally seen in clinical practice but unreported because they can only be explained by such unscientific, abstract models.

 

[Simon Bridge]

I am left with the explanation that I heard within the oral tradition of medicine created by pragmatic clinicians rather than the academic scientists of medicine. This simply attributes the control of cellular differentiation to the mysterious abstract mind, as if it contains a map of how the body should be and also uses this as an explanation for placebo effects, pain and certain bizarre phantom limb effects that are occasionally seen in clinical practice but unreported because they can only be explained by such unscientific, abstract models.

It is unfortunate that so many clinicians follow pseudoscience.

None of these models amount to an explanation either - it is more honest just to say "I don't know exactly but..."

One does not need to invoke some mystical mind-over-matter to account for things like the placebo effect though ... but that's a topic for another thread.

Monique's "they are programmed to" does beg the question "where did the program come from?"
But we do know quite a bit about how the program works - for instance - by observing stem cells in action.
Science is a work in progress a long way from finished - but we are farther along than you seem to think.

 

[Monique]

Monique's "they are programmed to" does beg the question "where did the program come from?"

The program comes from proteins that are able to bind the DNA and activate or repress transcription. A lot is known about it, researchers in Japan are able to create different brain cells by sequentially exposing induced pluripotent cells with such proteins. The clues on what order to present the proteins came from normal brain development: just look in what order they are expressed normally.

 

[Monique]

The Hox example is a good one, the following figure shows how a group of genes regulate the body plan.

What happens when there is a mutation in the Hox gene:
http://dermatology.cdlib.org/124/case_reports/dysplasia/3.jpg

 

[Simon Bridge]

Yes we do know quite a bit about how the program works :)
Those are excellent examples.

I wouldn't mind people observing "science does not know everything" so much if the people in question had a better grasp of what science does know. I could probably run through the list of things in Tzikin's last paragraph there but it is better done in a different thread.

 

[DiracPool]

Monique is right, this is just evo-devo stuff, life had 3 billion years to put this together

 

[DiracPool]

I recommend this book, its an easy read and will answer all your questions...

http://seanbcarroll.com/books/Endless_Forms_Most_Beautiful/

 

[Monique]

Fruit fly with legs in the place of antenna:

Won the nobel prize in 1995 http://www.nobelprize.org/nobel_prizes/medicine/laureates/1995/illpres/lewis.html

 

[DiracPool]

Why do you keep grossing me out, Monique?