October 7 Lecture - October 7, 2008 Appositional Growth -...

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October 7, 2008 Appositional Growth - Another form of growth that takes place in bone - Growth in thickness not in length - Growth at surface of the bone - Cells in the periosteum develop into osteoblasts which are bone generating cells which begin producing bony tissue at the surface (just beneath the periosteum) - The endosteum (which lines the marrow cavity) develop osteoclasts which resorb bone from the inside of the shaft o Bone degeneration - Hard bone (compact bone) is being produced Endochondrial Ossification - Ephyseal plate remains cartilaginous and acts as the centre for growth to take place within long bones - The outer surface of the ephysis region will also remain cartilaginous which will eventually give rise to the articulated part of the bone - Ossification takes place on the underside of the cartilaginous tissue of the ephysis and the lower boundary of the ephyseal plate - Process continues throughout adolescence (early 20s begins to slow process) and cartilage will eventually stop producing growth and ephyseal plate will eventually become filled - Growth will stop at this point Bone Remodelling - Bones over time will however be remodelled over time (5% of bone tissue approximately are being remodelled over time) - Involves resorbed bone and appositional growth in osseous tissue - Benefits of bone remodelling: o If bone has undergone any trauma and has been damaged, damaged tissue can be replaced (ex. fractured bone is repaired by remodelling) o Allows bone to respond to stress o Bone can increase in strength o Orthodontists rely on this procedure: braces force part of the jaw bone to remodel so that teeth are in proper alignment (slow process but effective under proper supervision) o Allows bone to be reshaped so that it may provide proper support based on stress patterns that are exerted o New bone tends to be more resilient than old bone (less likelihood of fractures taking place in skeleton) - Remodelling relies on many vitamins and hormones o Hormonal Factors include: Parathyroid hormone (PTH): produced by the parathyroid glands, responsible for the resorption of calcium from bone as bone is degenerated, increases the amount of calcium in blood. Regulates calcium
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levels in the blood to maintain relatively constant levels 10 mg / 100mL of plasma. If level is too low or too high there are several effects cardiac arrest, reduced respiration, muscular impairment, neurological functioning. 99% of bone tissue is calcium (large calcium storehouse)
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This note was uploaded on 10/23/2011 for the course BIOL 2125 taught by Professor Dr.park during the Winter '02 term at A.T. Still University.

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October 7 Lecture - October 7, 2008 Appositional Growth -...

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