The Skeletal System Wednesday October 10 2012 12 21 PM Composed of 2 organs bones cartilage 206 named bones Classes of Bones shape Long bone Diaphysis long axis shaft composed of dense bone tissue surrounding the medullary cavity contains bone marrow red or yellow a Red marrow source of the blood cells in children b Yellow marrow does not produce blood cells in adults Diaphysis surrounded by the Periosteum a Fibrous Outer layer Composed of dense irregular connective tissue blood vessels enter the compact bone of diaphysis through the Nutrient Foramina b Osteogenic Inner layer Osteoblasts formed in cells Osteoclasts bone resorbing cells breakdown Nutrient Foramina into the perforating Volkmann s canal to join the cavity in the osteon called the Haversion canal Periosteum us secured to the external surface of the diaphysis by tough cord like structures called Harpey s Fibers Epiphysis slightly expanded ends of the long bones composed of spongy bone tissue with a thin plate of periosteum covered compact bone on the outside Spongy bone is composed of trabeculae the surfaces are covered by connective tissue membrane called the Endosteum Blood vessels from the perforating anal extend into spaces between the trabeculae of spongy bone contain red bone marrow to produce blood cells 1 Red bone marrow in epiphysis and diaphysis 2 Epiphyseal plates composed of hyaline cartilage at the diaphyseal epiphysial junctions 1 Red bone marrow only present in spongy bone of epiphysis 2 Epiphyseal lines remnants of plates Child s long bone metaphyses Adult s long bone Short bone Flat bone Irregular bone Types of Bone Tissue texture Spongy composed of Trabeculae needle like structures Compact composed of Osteons concentric rings Bone tissue surrounded by connective tissue infiltrated by blood vessels and nerve fibers Ossification development of the bony skeleton from the embryonic skeleton Prenatal ossification occurs before birth a Intramembranous ossification Mesenchyme secretes membrane called fibrous connective tissue located in the skull clavicles these cranial bones and clavicles derived from fibrous CT membrane via intramembranous ossification 8 cranial bones 2 clavicles Flat bones membrane bones All membrane bones are flat bones b Endochondral ossification Mesenchyme chondroblasts secrete hyaline cartilage bone tissue Bones formed via endochondral ossification all bones except 8 cranial 2 clavicles Long short irregular and some flat bones are formed Long hyaline cartilage long bones hyaline cartilage still persists in the articular cartilage and epiphyseal plates After endochondral ossification short irregular and some flat bones the hyaline cartilage is completely changed into bone tissue Endosteum covered spongy bone surrounded by thin plates of periosteum covered compact bone Postnatal ossification ossification after birth a Longitudinal bone growth possible due to presence of epiphyseal plates Active zones in epiphyseal plates Epiphyseal plates Diaphyseal plates 1 Growth zone Chondroblasts proliferate increase in number via mitosis increase in chondroblasts will result in an increase of new hyaline cartilage secreted onto the epiphyseal face of the epiphyseal plates 2 Hypertrophic zone Chondroblasts have matured into chondrocytes and the chondrocytes increase in size growth of the chondrocytes via hypertrophy increased demand of nutrients by the enlarged chondrocytes 3 Calcification zone Calcium phosphate salt crystal moves into the semisolid matrix of the hyaline cartilage solid matrix which cuts off nutrients to the chondrocytes chondrocytes die 4 Ossification osteogenic zone Osteoblasts migrate into the deteriorating hyaline cartilage matrix to secrete new bone tissue on the diaphyseal face of the epiphyseal plates epiphyseal plate has been shifted linear bone growth 5 Resorption zone Osteoclasts will cause slight resorption of the nearly formed bone tissue to lengthen the medullary cavity in the diaphysis b Apparitional bone growth Osteoblasts secrete Osteoclasts resorb Hormonal Control of Postnatal bone growth Growth Hormone growth promoting effect of growth hormone on longitudinal bone growth is indirect stimulates the hepatocytes to produce IGF s IGF s bind to IGF receptors on the chondroblasts to stimulate their proliferation Increase in the number of chondroblasts increase in new hyaline cartilage added on the epiphyseal face of the epiphyseal plate stimulate ossification Childhood Gigantism Sex Steroid Hormones a Males Androgens Testosterone b Females Estrogen Estradiol Synergize work well with growth hormone IGF increase increase in longitudinal bone growth After period of about 5 yrs sex steroid hormones categorize growth hormone from stimulating IGF synthesis by the hepatocytes decrease IGF decrease new hyaline cartilage secreted on the epiphyseal faces of epiphyseal plates Sex steroid hormones stimulate ossification of the epiphyseal plates Rate of ossification outpaces formation of new hyaline cartilage Entire epiphyseal plate becomes ossified leaves epiphyseal line Complete ossification of epiphyseal plates at the metaphyses of long bones Epiphyseal Plate Closure Longitudinal bone growth ceases height is determined New bone tissue added on external surface Osteoblasts Old bone tissue is slightly resorbed from internal surface Osteoclasts Creates thicker but lighter bone Appositional Bone Growth Increased diameter thickness Occurs throughout life in ALL bones long short flat irregular Rate of Bone formation Rate of Bone resorption Osteoporosis when rate of resorption is ahead of rate of formation more hollow but still small in size Bone Remodeling Occurs throughout lifetime Coordinated event involving bone formation and resorption based on physiological needs of individual Function Calcium homeostasis 99 of calcium is stored in bone matrix Ca2 ionic calcium involved directly indirectly in all physiological processes in the human body Strictly regulated and maintained in body Hypocalcaemia Less than 9mg calcium in blood released from blood tissue to bring back to normal levels Hypercalcaemia More than 11mg calcium in blood calcium deposited in bone tissue Purpose of bone remodeling Fractured bones are healed by the synthesis and mineralization of new bone tissue Fracture rate of bone formation to outpace the rate if bone resorption Normal Rate of Bone formation Rate of Bone resorption Osteoporosis Pathophysiological disease state When rate of resorption is ahead outpaces of
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