Early Bone Development 2 patterns of bone development intramembranous ossification cranial bones and clavicles and endochondral ossification long bones humerus femur tibia etc In intramembranous ossification bone develops directly from mesenchymal tissue In endochondral ossification bone slowly replaces hyaline cartilage Calcification takes place as osteoblasts start depositing hydroxyapatite calcium and phosphate ions precipitate to form crystals During this process osteoblasts slowly change phenotype and transform into osteocytes Bone synthesis requires requires vitamin D3 facilitates Ca absorption in the digestive system among other things and vitamin C ascorbic acid required for collagen formation Intramembranous Ossification The original layer of mesenchyme is sometimes referred to as a membrane hence the name intramembranous ossification Intramembranous ossification follows four steps a Mesenchymal cells group into clusters and ossification centers form b Secreted osteoid traps osteoblasts which then become osteocytes c Trabecular matrix and periosteum form d Compact bone develops superficial to the trabecular bone and crowded blood vessels condense into red marrow Endochondral Ossification a Mesenchymal cells differentiate into chondrocytes b The cartilage model of the future bony skeleton and the perichondrium form c Capillaries penetrate cartilage Perichondrium transforms into periosteum Periosteal collar develops Primary ossification center develops d Cartilage and chondrocytes continue to grow at ends of the bone e Secondary ossification centers develop f Cartilage remains at epiphyseal growth plate and at joint surface as articular cartilage Longitudinal Bone Growth The epiphyseal plate is responsible for longitudinal bone growth This process is stimulated by sex steroid hormones mainly oestrogen Growing Long Bone Mature Long Bone https www dartmouth edu anatomy HAE Lowerextremity leg radiology APknee child html As a bone matures the epiphyseal plate progresses to an epiphyseal line Epiphyseal plates are visible in a growing bone left Epiphyseal lines scars are the remnants of epiphyseal plates in a mature bone right The evolutionary advantage of having hollow bones https www quora com Why do birds have hollow bones and lightweight beaks https dickinsoncountyiowa org conservation wp content uploads sites 2 2019 10 1 s2 0 S136970211730072X gr5 lrg 1024x772 jpg Hollow vs Solid Shafting February 27 1869 Hollow shafting where large diameter is not objectionable has long been in use made generally of cast iron and frequently used as a drum or continuous pulley for the reception of belts Such a shaft was used in the pistol shop of Colt s factory before the destruction of the building by fire about four years ago and a similar line may now be in use in the reconstructed building This shaft was five hundred feet long and fifteen inches diameter made of hollow cast iron cylinders connected with each other by a solid shaft or bearing at each end resting in a box as a journal The result was an almost continuous drum of five hundred feet in length from which belts led to the counter shafts of the machines the speed of each machine being regulated by the diameter of the pulleys on the counter shafts We have heard also of wrought iron pipes of only two inches diameter being used as shafting successfully Tredgold says that a round tube whose internal and external diameters are as seven to ten respectively has twice the lateral strength of a solid cylinder containing the same amount of material A cylinder solid of cast iron five inches diameter has a transverse strength of 21 104 pounds while one of eight inches diameter containing the same cross sectional area of metal has the transverse strength of no less than 45 416 pounds These facts would seem to show plainly the possibility of reducing the weight and material of shafting without a diminution of its strength The weight of shafting is a mass the inertia of which must be overcome by the driving power and in some cases the amount of power otherwise useful that in thus absorbed is not less than twenty per cent If by the use of lighter shafting this could be reduced only five per cent the saving would be worth an effort Shafting must be of sufficient diameter to sustain the weight of pulleys and the strain of belts without springing but if the requisite stiffness resistance to torsion and springing can be obtained by hollow shafts of much less weight not only is money saved in the first cost shafting being furnished by the pound but the continual expense in the absorption of unnecessary power in driving the unnecessary weight would also be prevented That hollow shafting of wrought iron can be made cheaply is sufficiently apparent when we examine specimens of piping for various purposes And not only would the first cost be less but the ease of handling owing to reduction in weight would lessen the cost of turning etc Such shafting could also be easily oiled from the inside which would seem to be the proper method This article was originally published with the title Hollow vs Solid Shafting in Scientific American 20 9 137 February 1869 Sometimes even hollow is not good enough Types of Fractures Stages in Fracture Repair The healing of a bone fracture follows a series of progressive steps a At first a hematoma forms b Within 48 hours post injury internal and external calli form chondrocytes from the endosteum created an internal callus by secreting a fibrocartilaginous matrix between the two ends of the broken bone while the periosteal chondrocytes and osteoblasts create an external callus of hyaline cartilage and bone c Cartilage of the calli is replaced by trabecular bone d Remodeling occurs A doctor who focuses on repairing functional abnormalities of bones is call an orthopedist Bone remodeling Wolff s law Suggests that bone adapt to the load under which it is placed