How Do Osteocytes Receive Their Nutrients?

00:01 So let us get on now to look at how osteocytes do receive their nutrients. Well, on this image, it is really a high magnification of an osteon. It has a central osteonal canal or Haversian canal and let us just go through the main points about the osteons that I mentioned earlier. The canal is lined by endosteal cells. Endosteal cells line also all the spicule bone, all the trabecular bone that we see up in the cancellous and spongy regions of the bone. Endosteal cells line the internal medullary cavity, and periosteal cells line the outside capsule of bone, the periosteum. So bone is never naked. If it is naked, if it is bare, the bone dies. And that is because if you look at this image, when blood vessels, blood capillaries pass up through the Haversian canal and all the nutrients leak out of these capillaries into the Haversian canal, they then get pumped across into the very fine canaliculi by the endosteal cells. And because all the osteocytes are in contact with these endosteal cells, and are linked together through these little canaliculi, the nutrients once pumped across the surface of these endosteal cells into the canaliculi can then be accessed by all the osteocytes. Even those are long long way away from the Haversian canal.

01:51 So they receive their nutrients via endosteal cells. And as I mentioned before, if these endosteal cells die, as sometimes happens in bone cancers, then the bone is naked. The nutrients cannot be pumped across into the canals and, therefore, the osteocytes cannot receive nutrients and so die. So it is important for you to understand now how these bone cells get their nutrition even if they are embedded in this very hard calcified matrix.

02:27 Well, let us just review what we have covered so far in looking at the structure of mature bone. Remember there are two types of bone histologically, spongy or cancellous bone and hard or compact bone. And remember that all those bony spicules you see and even the outside capsular bone, they are all lined by either endosteal cells or periosteal cells.

03:04 And the important thing about that is that if you break a bone, those endosteal cells and the periosteal cells can initiate bone formation and bone growth and bone repair. So not only are those endosteal cells important for providing nutrition to the osteocytes embedded in the lamellae, those endosteal cells are also important for repairing bone should it be injured.

03:35 Bone is never naked because of that reason, because the importance of these endosteal cells to provide nutrition to the bone. So that will cover mainly the structure of mature bone and how these bone cells get their nutrition. In a later lecture, I will explain how bone is formed and then how bone grows.