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Posted

There is an age beyond which growth ceases, if that's what you mean. The major limiting factor is our long bones, such as the femur. Rather than being remodeled as a whole, like ribs and such, these bones have two regions at each end, just before the joints, which are essentially just a cartilage disk. These disks, called epiphyseal plates, are why kids break bones so often (it's a natural weak point), but also allow the bone to simply add material at those points, thereby lengthening rather simply. After a certain age, the epiphyseal disks are completely replaced by bone, and no more growth occurs. What age that is varies, but is usually somewhere between 21-25.

 

Mokele

Posted

But see that is what I find weird

 

Most of your bones are just bone marrow is it not? The outer shell that we see is a very thin layer.

 

The body is not able to add onto that?

 

But then can it be worn down then? Can we get shorter

Posted
Most of your bones are just bone marrow is it not? The outer shell that we see is a very thin layer.
There's a skin-type layer on the outside of the bone, then the compact bone (the dense stuff), then the spongy bone (more porous), then the blood vessels and marrow.

 

Most of your bones is not marrow.

 

Bones do change shape as we age and can make us shorter. I don't think this is due to erosion as much as gravity and weakening. Facial bones alter and it can give us wrinkles and sags we didn't have before.

Posted
Most of your bones are just bone marrow is it not? The outer shell that we see is a very thin layer.

 

It depends on the type of bone. Most bones, like ribs, skull bones, vertebrae, the pelvis, etc, don't have marrow. There's a thin layer of connective tissue, a thin layer of compact bone, and then the rest is filled with spongy, trabecular bone.

 

Long bones (leg and arm bones) are different; the center of the shaft (diaphysis) is hollow and free of trabecular bone but rather contains marrow, and the compact bone layer is very thick in the shaft (though not necessarily so in the ends).

 

The body is not able to add onto that?

 

Oh, it can, and does; your non-long bones (everything but arms and legs) grow too, by adding and remodeling the bone at the celluar scale (via cells within bone which erode it away and deposit more). The epiphyseal disks are just a cheap and easy way of making the long bones longer without as much mucking about.

 

But then can it be worn down then? Can we get shorter

 

Yep, that's osteoporosis, a common problem in old people. New bone isn't deposited as fast as old bone is eroded, so the skeleton becomes weak and brittle. Their limbs don't shrink, though, just become more easy to break (old people do get shorter, but that's due to vertebral problems).

 

Not according to a study by the American Society of Plastic Surgeons. But maybe they make more money from bone grafts for aging starlets.

 

While the facial bones *do* change (and plastic surgery can reverse that), the actual sagging and wrinkling is more due to loss of skin elasticity from collagen.

 

Mokele

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