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Created by Tracy Kim Kovach.
Video transcript
ok so now let's talk about the cellular structure of loan you can think of bone as being mostly made up of the bone matrix and then the cells that actually helped to form this bony matrix now the majority of bone is made up of the bone matrix which consists of two principal building blocks the first of which is called osteoid and this forms the organic portion of the matrix and then you have something called hydroxyapatite which forms the inorganic portion of the bone matrix so first let's talk about the organic portion of the bone matrix the organic portion of the bone matrix is made up of like I said osteoid which consists of a soft but highly ordered structure of proteins and then collagen specifically type 1 collagen so together the orientation of these highly organized collagen fibers along with the proteins helps to give bone its tensile strength so what does tensile strength really need if you think about a really hard piece of rubber like a rubber eraser for example I kind of think of tensile strength is being somewhere to the way that piece of rubber gives ever so slightly if you were to push on it but it still holds its shape and so that's when you can think of as bones tensile strength now for the inorganic portion of bone the inorganic portion of bone is made up of hydroxyapatite and i'll draw its chemical formula here it is calcium along with phosphate and water so basically all hydroxyapatite of is calcium phosphate crystals and these calcium phosphate crystals are the mineral portion of bone that gives bone its rigid strength and density so now you have a better understanding of the osteoid or organic portion of the bone majors and hydroxyapatite which make up the inorganic portion of the bone matrix so now let's talk about the cells that are actually responsible for making up this bony matrix there are four different types of cells to be familiar with in bone and the first group are the osteogenic ourselves next we have what are called osteoblasts then there are the osteocytes and finally we have the osteo class so you can see they all share the same route osteo meaning bone so let's make a little bit more room here and talk about each of these cells on by one and what they do so first step we have the osteo progenitor cells the cells are basically just the precursor to osteoblast so basically they're just an immature version of osteoblasts and they differentiate into osteoblasts under the influence of various growth factors so that brings us up to osteoblast now osteoblasts are the cells that are responsible for synthesizing both collagen and proteins specifically a couple of proteins called osteocalcin and osteopath on Tintin and together these makeup osteoid osteoma plants are also responsible for producing alkaline phosphatase which is the enzyme that is responsible for forming hydroxyapatite for the mineral portion of bone once osteoblast have synthesized enough collagen and proteins and alkaline phosphatase to form the organic and inorganic portion of the bony matrix around them and they're finally surrounded by all this they mature into the osteo site so the mature version of an osteoblast once it's all done synthesizing the bony matrix becomes an osteocyte so that brings us to osteocytes now the spaces that osteocytes occupy are called within bone are called lacunae and the term lacunae really just refers to an empty space within bone so under a microscope these spaces look to me like little leaks and so that's how I remember what lacunae are they are little lakes or absences empty spaces within bone and these osteocytes have little arms or branches that reach out to communicate with other osteocytes or osteoblast which kind of gives them that star like appearance and these little branches are like sensors that pick up new information send out signals basically allowing osteocytes to communicate with other cells that help to maintain bone and then the final cell type is the osteo class now on so class are derived from a cell line called Monica sites and they are responsible for bone resorption so basically they break bone back down again and they do this with an enzyme called tartrate resistant acid phosphatase so osteoblasts help build up on with an enzyme alkaline phosphatase and then osteo class help to break that bone back down again with an enzyme tartrate resistant acid phosphatase so bone is basically constantly being remodeled built up by osteoblasts and broken down again by osteo class and an easy way to keep this tree is to think that osteoblast the B and blast is for building bone and then osteoclast the sea in class osteo class is for crashing bone down so osteoblast build-up own audio class break it back down again now as osteoclasts are resolving bone they start to form little empty spaces and bone and wait what are empty spaces and bone called they're called lacunae and so just like osteo sides occupy lacunae osteoclast occupy special kind of lacunae called how ship's cook me which are just the little resort option pits formed by a co class as they break down the bone surrounding them