Bone Physiology. Bones are Classified by shape and structure limbsCarpals tarsals vertebrae Skull...

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Transcript of Bone Physiology. Bones are Classified by shape and structure limbsCarpals tarsals vertebrae Skull...

  • Slide 1
  • Bone Physiology
  • Slide 2
  • Bones are Classified by shape and structure limbsCarpals tarsals vertebrae Skull bones Ribs Sternum scapula
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  • Epiphysis Epiphyseal Line Diaphysis Periosteum Articulating Cartilage
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  • Compact Bone Canaliculi Haversian Canal Lamellae Osteon
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  • Another picture of Compact Bone
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  • Spongy Bone Located along the epiphyses of long bones Site of Erythrocyte (RBC) formation
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  • Cells in Bones
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  • Endochondrial Ossification Bone tissue in a fetus begins as hyaline cartilage Inside is cartilage, cartilage becomes ossified. In 6 weeks cartilage is replaced to bone except at growth plates.
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  • Longitudinal Growth at the Epiphyseal line
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  • Two growth plates Composed of hyaline cartilage Longitudinal growth is completed when epiphyseal lines become completely ossified.
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  • Chrondroblasts closest to epiphyses begin to undergo cell division Cells enlarge (hypertrophy) Cells die, bone eventually replaces cartilage (invasion zone)
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  • Resting Zone Mitosis Zone Hypertrophy Zone Ossification Zone
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  • Resting Zone Mitosis Zone
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  • Ossification Zone Maturation/Hypertrophy Zone
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  • Longitudinal Growth Controlled by 3 hormones Growth Hormone Baby to prepuberty Sex Hormones (estrogen/testosterone) Causes growth spurt at puberty Shapes your skeleton to your sex Thyroid Hormones (PTH & Calcitonin) PTH = parathyroid hormone Controls whether bone growth occurs Affects Appositional Growth bone growth in diameter
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  • Bone Homeostasis Bone Remodeling Osteons are formed by osteoblasts In healthy adults: Bone deposit = bone resorption Osteoblasts = Osteoclasts Bone Remodeling refers to the regular mineral turnover that occurs in bone. In adults, 18 % of proteins and minerals turns over yearly. Not uniform. I.e. Head of femur is remodeled more. Why?
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  • Bone Remodeling Controlled by Negative Feedback Loop Bone Deposit Occurs where bone is injured or added bone strength is required Deposits Ca +2 into bone Bone Resorption Osteoclasts break down bone Calcium is taken from bone and placed into blood stream Lysosomes assist in the process Ca and PO 4 are released; eventually releasing the blood stream
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  • Bone Remodeling is controlled by 2 hormones by a Negative Feedback Loop Blood Calcium is the original stimulus Normal Blood Ca is 9-11 mg CA/100 ml of blood When blood Ca decreases (< 9 mg) Parathyroid Hormone (PTH) is released into bloodstream. Bone resorption occurs causing Ca to leave bone and goto the blood stream Osteoclasts are working
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  • High levels of blood Ca (>11mg) When blood Ca levels are high, Calcitonin is released. Causes bone deposit to occur Ca from the blood is stored into bone. (Osteoblasts and Osteocytes are working.) 99% of all Ca is found in bone.
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  • Osteoclasts cause bone resorption Controlled by PTH Osteoblasts cause bone deposit Controlled by calcitonin
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  • Vitamin D aids in the absorption of Calcium into the bone. Part of vitamin D is converted to the hormone calcitriol which allows Ca to pass through the S.I.(What food is Vitamin D fortified?) i.e. rickets results from Vitamin D deficiency Vitamin C helps osteoblasts function i.e scurvy caused from a reduction in osteoblast activity Calcium tablets - Diet -
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  • 2 nd Response to Regulating Bone Remodeling Wolffs Law Bone grows or remodels in response to the forces or stresses placed on it. Appositional growth growth in diameter is controlled by the amount of mechanical stress and gravity placed on the bone Heavy usage leads to heavy bones; nonuse leads to atrophy (bone loss)
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  • Controlling Bone Remodeling Hormones PTH and Calcitonin determines whether and when bone remodeling occurs. Mechanical Stess determines where remodeling occurs. High stress areas grow appositionally.
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  • Bodys Needs for Calcium Transmit nerve impulses Muscle contractions Blood coagulation Cell division If blood Ca levels are low for an extended time, bones continually lose Ca. Once bone density loss begins, women lose 8% of their bone mass every decade, men lose 3% every decade
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  • Osteoporesis Normal Bone Risk Factors Sex (females more affected than males; especially after menopasue) Insufficient exercise or too much exercise Poor diet (low in Ca and protein Smoking Race: Black > bone density
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  • Change in Bone Density with Age
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  • Bone Fracture and Repair Simple Fractures take 8-12 weeks to heal Healing time increases age due to poor circulation
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  • Phases of Bone Repair A mass of clotted blood appears Blood vessels hemorrhage, causing internal bleeding Blood pools and clots around fx area; which closes off injured blood vessels
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  • Macrophages invade and clean area Fibroblasts help form chondroblasts and collagen fibers Helps to form cartilage splint that will connect ends of broken bones
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  • Osteoblasts replace the cartilage with spongy bone Bone cells replace cartilage from the outside fx toward the inside Cells are not organized in the bony callus
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  • Continues 4 months to a year Removes excess material; a layer of compact bone is produced
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