# How do we grow (physically)? **URL:** \ **Category:** Factual Questions\ **Created:** [April 15, 2010, 11:55am UTC](https://boards.straightdope.com/t/how-do-we-grow-physically/536194 "2010-04-15T11:55:13Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![NineToTheSky](https://avatars.discourse-cdn.com/v4/letter/n/b5a626/32.png) [@NineToTheSky](https://boards.straightdope.com/u/NineToTheSky)\ **Post date:** [April 15, 2010, 11:55am UTC](https://boards.straightdope.com/t/how-do-we-grow-physically/536194/1 "2010-04-15T11:55:13Z")
As we age, we grow taller. Logically, our bones, muscles, skin and pretty much everything else must get bigger. [ul] [li]How does this happen?[/li][li]Presumably, all the internal organs grow proportionally? [/li][li]How does, say, the bone in my left leg know to grow at the same pace as my right leg? [/li][li]Does skin stretch? [/li][li]What determines when you stop growing? [/li][li]Is there anything an individual can do to change the pace and amount of growth?[/li][/ul] ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [April 15, 2010, 1:22pm UTC](https://boards.straightdope.com/t/how-do-we-grow-physically/536194/2 "2010-04-15T13:22:45Z")
This is one of the biggest questions in developmental biology, and not all the factors are understood. What is becoming clear is that there a number of complex factors involved: Genetic Control: DNA controls what a cell does. However, the expression of that DNA is regulated by additional factors. Growth factors: these are hormones that trigger stem cell differentiation Nearest Neighbours: Cells differentiate differently based on the cells that surround them Environment: differentiated cells develop differently based on environmental factors - stem cells in a scaffold placed in a heart develop differently to those in a static environment. In general, organs modify themselves based on environment - an adult kidney transplanted into a child will shrink to an appropriate size, then grow as the body grows. A childs kidney implanted into an adult will increase in size over time as it adapts to the load. Bone/frame growth is regulated by a combination of genetic and environmental factors (if hormone regulation is normal) - malnutrition (for example) can easily override genetic size. Because the body is generally in equilibrium, the same factors have the same influence on symmetric development - legs and arms develop at the same rate. But not always - I have one leg a few cm shorter than another - I get asked if I am injured all the time, because I limp slightly \. Disease and misuse can easily impact on symmetrical development. Skin stretches and produces more collagen over time, but rapid stretching can produce stretchmarks - areas of scarring where insufficient skin cells have formed during rapid expansion. Similarly with shrinkage - there can be some shrinkage with time, but rapid shrinkage (as with severe weight loss) can leave excess skin. There is a theory that humans rapid scar formation actually interferes with proper cellular level repair by blocking stem cells from the injury site. Drugs/therapies that gently remove scar tissue and allow cellular regeneration are now being investigated, particularly in the case of nerve damage. But I would not hope for limb regeneration for many, many years - if ever. Si ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 15, 2010, 2:21pm UTC](https://boards.straightdope.com/t/how-do-we-grow-physically/536194/3 "2010-04-15T14:21:53Z")
> [@NineToTheSky](#): > > [li]Does skin stretch? [/li][li]Is there anything an individual can do to change the pace and amount of growth?[/li][/LIST] Skin will grow (i.e. the cells will multiply) in response to constant stretching. ISTR surgeons implanting balloons under the skin of patients to cause the skin to grow; the intent is to produce extra skin they can harvest for some major, non-urgent surgical procedure they plan to do on that same patient in the near future.