 Hey everybody, Dr. O here. Let's talk about bone as a tissue. So remember we talked about bone as a supportive connective tissue back in the histology chapter. The specialized cells, we covered the bone cell types. You can see here that there are osteocytes, these mature bone cells are going to be in these lacunae, these cavities are openings, just like you saw with connective tissue. So the four key characteristics of bone as a tissue is going to be this very dense matrix. So surrounding these bone cells that are in these cavities is going to be, is going to be the minerals, especially going to be your calcium and then there's also going to be protein fibers, all connective tissues have protein fibers and the protein fibers are going to be collagen. So surrounding your bone cells you have this dense matrix of calcium tissue plus other minerals plus the protein that gives it some flexibility. Also looking at just a functional unit of bone tissue is going to be an osteon here. So I already talked about the osteocytes, the mature bone cell covered, covered in bone. The canaliculi there are going to be how blood vessels get in and out so they can trade nutrients and waste products. You will see that this is going to be compact bones. You have a very organized concentric layers of bone cells with mineral tissue. You don't see that in your spongy bone. I think that's all, that's the key to look at here as far as an individual osteon. Let's go ahead and look at the bone tissue though that the fourth, the fourth characteristic of bone is going to be that skin on the outside called the periosteum which I'll show you right there. So your bone is going to be made of these osteons and they're going to have that dense bony matrix of calcium. The hydroxyapatite is probably the most important term here but calcium phosphate reacts with calcium hydroxide to form this calcium hydroxyapatite which incorporates all these calcium salts and crystallizes. That's how bone hardens. So the hard part of bone is going to be this matrix of minerals, primarily calcium. But then about one third of your bone is going to be protein fibers and that's going to be collagen. So remember the minerals in bones give it the density it needs, the collagen gives it the flexibility that it needs and the far as the bone cells, the osteocytes you see scattered around here, they only make up about two percent of the mass of your bones. So if you're looking at a compact bone, I think we've said when you say there, the osteons are going to be the key, the functional unit. Notice that all the osteons in compact bone are running in one direction which is why they're so strong and the bone is strong in that direction. Like you look at a femur, a femur can withstand you jumping off of a table and the shock that comes with that but if a football helmet hits the side of the femur it can snap it relatively easily because that's not the direction that the osteons are lined up. So spongy bone, you're going to see a real open, trabeculated pattern here. You do still have bone cells, you have the endosteum, the skin on the inside of here but instead of having these nice organized osteons, what you have is this, this trabeculated pattern and inside of that you're going to see the red bone marrow which is going to produce, it's red because it produces blood cells including red blood cells. Alright, so that's the basics of histology or the tissue that makes up your bone. I hope this helps. Have a wonderful day. Be blessed.