 Hello everyone welcome back to another session in the industry and more today's topic is bone formation or ossification. So we know the bone formation happens at the very early years of life. So bone formation happens in two ways basically one is intra cartilaginous way that is endocontrol and the second one is intra membranous way. So the pattern of ossification is different in these two methods. First let us learn about bone formation. So we will start with the endocontrol bone formation which is also known as intra cartilaginous one. So the basic difference between these two is in intra cartilaginous one there will be a template there will be a cartilage template or cartilaginous model which serves as a foundation for the future bonds. So we know Mackel's cartilage we have learned Mackel's cartilage in our embryology. Mackel's cartilage in pharyngeal pouches pharyngeal arches where this Mackel cartilage act as a template for many bonds such as malleus ingus. So this was nothing but endocontrol bone formation that is there will be a template for the future bone formation. That is the basic difference this intra membranous there is no such template or there is no such a foundation where the future bone develops it is only for endocontrol bone formation. So we will start the steps of endocontrol bone formation. So it starts with mesenchymal cells they become condensed at the site of bone formation. So imagine this as a area where the future bone develops. So in that area mesenchymal cells become condensed and some mesenchymal cells differentiate into controblast. So some of the mesenchymal cells become controblast and it lay down the hyaline cartilage. So this cartilage is surrounded by a membrane called pericontrium pericontrium is a membrane which surrounds the cartilage. So this pericontrium is very highly vascular and which contain the osteogenic cells from which the future bone develops and then the intercellular substance surrounding this cartilage. So this is a cartilage. So intercellular substance surrounding this cartilage becomes calcified due to the influence of enzyme that is alkaline phosphatase which is secreted by this cartilage cells. So these are the cartilage cells which secretes alkaline phosphatase. So alkaline phosphatase causing the calcification of intercellular substances that is the blue dots. So the nutrition to this cartilage cells is cut off leading to their death because all the areas surrounding this cartilage is calcified. So the nutritional supply to this cartilage cells is gone. Then there will be death of these cells which results in formation of empty spaces okay empty spaces which is known as primary areole. So this is the process. So pericontrium then the gondroblast then gondroblast secretes alkaline phosphatase there will be intercellular calcification then the nutritional supply will be cut off and these gondro sites or gondroblast area will become dead and it will be a empty space which is known as primary areole all are the primary areole spaces. Then the blood vessels and osteogenic cells from the pericontrium invade the calcified cartilaginous matrix that is now reduced to bars or walls due to the eating away of the calcified matrices. So then the calcified matrices so all these intercalcified matrices what happens these matrices now invaded by the pericontrium osteogenic cells okay. So this leaves a large empty spaces between the walls called as secondary areole. So all these intercellular substances are invaded and it becomes like this that is walls of empty spaces okay this is known as secondary areole and then what happens then the osteogenic cells from the pericontrium becomes osteoblast okay. So this is a osteoblast and they arrange along the surface of these bars of calcified matrices okay. So this portion is enlarged here okay. So this is lined by osteoblast okay. So after that what happens after that there will be osteoid formation okay. So then these osteoblasts will lay down osteoid that is the immature bone okay which later becomes calcified and becomes lamella of bone okay this is the future bone that is a calcified bone at the same time the next layer of osteoid is formed by the help of these osteoblasts and it goes on okay. This is how endocontrol bone formation happens. Controblast then the pericontrium the primary areole secondary areole then the osteoblast then the osteoid formation then the lamella bone and the new osteoid formation and it goes on okay. So primary areole is becoming secondary areole by the dissolution of intercellular calcified structure and it becomes like this and each one is surrounded by osteoblast. Now let us move on to the intramembranous one. So intramembranous one contradicting to the endocontrol formation there is no formation of cartilaginous model instead the bone is laid down directly in the fibrous membrane. So this is the fibrous membrane where the bone is laid down directly in the fibrous membrane. So it starts with again the mesonchym. So there will be mesonchym cells which will be aggregated at the site of bone formation that is the first step then what happens then some mesonchymal cells lay down the bundles of collagen fibers. So there will be bundles of collagen fibers after that some mesonchymal cells enlarge and acquire a basophilic cytoplasm basophilic cytoplasm and form osteoblast. So some of the cells becoming osteoblast. So these osteoblasts secrete gelatinous matrix called osteo. So we also seen osteoid here that is a mineralized bone. So osteoid formation happens and this conversion of osteoid into bone lamellae by deposition of calcium salt. There will be calcium salt deposition and it becomes the lamella bone and these osteoblast move away from the lamellae and the new layer of osteoid is secreted which also get calcified. So this was the first bone okay first bone formed then it starts again secreting osteoid this is a osteoid okay. So it will be continued. So the process is almost same osteoid becomes a new bone and the process continues. When this osteoid forms and it becomes a lamella bone the osteo sites or osteoblast move away from it and a new layer of bone will be laid down. So only difference between these two endocontrol and intramembrane is in endocontrol we have a template here we do not have it forms directly within the membrane okay. So what are the bones actually follows this pattern. So the intramembrane is one okay they are cranial vault mandible clavicle all follows this intramembrane is bone formation or ossification. So the endocontrol or cartilaginous are mostly the vertebrae and longer bones and also we have learned the Michael's cartilage bones that is myelosincus and all those head and neck bones. So that is all about the bone ossification or bone formation we have endocontrol and intramembrane is types. So that is all for now hope you understood the basic concept of these two types of bone ossification I will come up with a new topic in dentistry and more thank you. And lastly guys we have started channel membership in dentistry and more channel. So you can explore various exclusives for the channel members. So you can explore various options by clicking on the join button adjacent to subscribe button. So we have options of personal whatsapp help. So you can ask any doubts you will get answered through whatsapp text messages or voice messages and we have one more option that is the pdf notes will be available but as of now we have only the public health dentistry topic. 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