Week 8 - Bone Growth: Explain Bones Are Not Just Calcium???

 
Week 8 - Bone Growth: Explain
Bones Are Not Just Calcium???
 

Before we try to uncover how Luís's bones grew - and why they seem not to be growing taller now - we should remind ourselves of what is in bone.  Most people would quickly point out that our bones are made of calcium.  After all, kids in the United States often hear that they should drink milk to get calcium for strong bones!  While calcium is an important part of our bone tissue, it is not the only or even primary ingredient!  Our bones include a lot of protein, in the form of collagen, which you might remember as a main component of the dermis of our skin and of cartilage.  Collagen is a strong protein with just enough elasticity to provide bones with some resistance to fracture.  In creating bone, our osteoblasts first lay down a collagen mixture, called osteoid.  They then mineralize the bones with a calcium phosphate mixture to make the bone hard.  That's where the calcium comes in!

mineralization of bone

Take a look at the diagram on this page, which shows how we think osteoblasts mineralize bones - a process physiologists still don't entirely understand.  I bring this in, because it shows a couple physiological concepts we studied earlier at work again!  For example, note the arrow on the left showing calcium and phosphate moving through osteoblasts and into the bone.  Physiologists think that osteoblasts use a combination of facilitated diffusion and active transport to shuttle calcium and phosphate from the blood into bone.  Of course, we know one of those methods would be necessary, since calcium and phosphate are charged chemicals (so hydrophilic) and could not move by simple diffusion.  Also note the arrows on the upper right showing two types of cell junctions.  Remember that cell junctions are physical connections between cells formed by membrane proteins.  Physiologists have shown that osteoblasts work in teams with each osteoblast physically connected by cell junctions.  That helps the osteoblast teams coordinate their efforts.

 
Ways of Growing Bones
In this module we will be exploring two different methods our cells have for laying down osteoid and performing mineralization to grow bones.  One of those methods of bone growth, endochondral ossification, is especially relevant to our scenario surrounding Luís and his desire to grow taller later in life.  Endochondral ossification is quite the long and complicated-sounding term, but it's not nearly as tricky as it sounds!  It's most helpful to remember that "chond" refers to cartilage and "os" refers to bone.  Put that together with "endo" (which means "within") and you get the definition of endochondral ossification - within cartilage bone formation.  We're going to try to see how this type of bone formation occurred in Luís's body and why it seems to have stopped.