Osteoblasts!

So, I opened up my good old Wheater's histology textbook (Young et al. 2006) and began reading up on osteoblasts. I was reminded that osteoblasts pretty much lay on top of mineralized bone matrix. It forms sort of a coating along the entire inner surface.

What caught my attention was how the authors described the process of laying down new bone. I made a quick sketch of this process in figure 1. The authors describe the osteoblasts as being spindle shaped when they are inactive. This is shown in the first panel. When laying down osteoid or new bone, the osteoblasts enlarge into cuboidal shaped cells, as shown in the third panel. Finally, they slowly return to their spindle-shaped forms as they lay down calcium hydroxyapatite (this is what hardens the newly laid osteoid).

FIGURE 1

Thinking about what they said visually and spatially, however, I found it slightly confusing. What do they mean by spindle-shaped. Are they referring to the appearance of the osteoblasts in histological slides? That they appear to be a thin spindle from a lateral view? If this is so, are they actually squamous cells cuts in sections? Or are they like muscle fibres, elongated cells? If they are, then how do they become cuboidal in nature? Do they increase in mass laterally and vertically?

Note that the following illustrations assume that osteoblasts are squamous and increase in height perpendicular to the bone surface. But with this assumption, there came another problem! Does an osteoblast maintain a generally constant volume when inactive and active (Figure 2b)? This question is not addressed in the textbook, and I'm pretty sure the prof didn't mention it either... If the answer if no... then would a lateral view appear like Figure 2a?

FIGURE 2

Such questions may appear to be relatively irrelevant, mundane, or trivial I suppose. For sure, I never thought to analyze osteoblast like this when I first learn of them. But, now that I plan on animating such cells, it's suddenly a huge deal! Well, maybe not super huge, but I would venture to say that such a consideration would have an immense impact on the credibility or captivity of an animatic piece. Could these sketches (Figure 3) provide any insight into the actual structure or functionality of osteoblasts that I have not yet figured out...? Most likely not, someone's probably done it. But, I'm sure it will come in handy when it comes down to the modeling and 3D interactivity.

FIGURE 3

So Figure 4 here is a redraw of my first comic strip (Figure 1) with consideration of volume and overlap, as seen from a lateral view.

FIGURE 6