The Skeletal System: Bone Tissue Chapter 6. Copyright 2009, John Wiley & Sons, Inc.

Transcription

1 The Skeletal System: Boe Tissue Chapter 6

2 Fuctios of Boe ad Skeletal System Support Protectio Assistace i Movemet Mieral Homeostasis Blood Cell Productio(Hemopoiesis) q Triglyceride Storage q Yellow boe marrow Triglycerides stored i adipose cells q Serves as a potetial chemical eergy reserve

3 Structure of Boe Log Boe Aatomy (Humerus) q Diaphysis q Epiphysis q Metaphysis Epiphyseal growth plate q Articular cartilage Perforatig fibers q Periosteum q Medullary cavity q Edosteum

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5 Histology of Boe Tissue Extracellular matrix surroudig widely separated cells q Matrix 25% water 25% collage fibers 50% crystallized mieral salts The most abudat mieral salt is calcium phosphate

6 Histology of Boe Tissue A process called calcificatio is iitiated by boe-buildig cells called osteoblasts Mieral salts are deposited ad crystalize i the framework formed by the collage fibers of the extracellular matrix Boe s flexibility depeds o collage fibers

7 Histology of Boe Tissue Four types of cells are preset i boe tissue Osteogeic cells q Udergo cell divisio; the resultig cells develop ito osteoblasts Osteoblasts q Boe-buildig cells q Sythesize extracellular matrix of boe tissue Osteocytes q Mature boe cells q Exchage utriets ad wastes with the blood

8 Histology of Boe Tissue Osteoclasts q Release ezymes that digest the mieral compoets of boe matrix (resorptio) q Regulate blood calcium level

9 Histology of Boe Tissue Boe may be categorized as: q Compact q Spogy

10 Histology of Boe Tissue Compact Boe q Resists the stresses produced by weight ad movemet q Compoets of compact boe are arraged ito repeatig structural uits called osteos or Haversia systems q Osteos cosist of a cetral (Haversia) caal with cocetrically arraged lamellae, lacuae, osteocytes, ad caaliculi

11 Histology of Boe Tissue Osteo q Cetral caals ru logitudially through boe q Aroud the cetral caals are cocetric lamellae Rigs of calcified matrix (like the rigs of a tree truk) q Betwee the lamellae are small spaces called lacuae which cotai osteocytes q Radiatig i all directios from the lacuae are tiy caaliculi filled with extracellular fluid

12 Histology of Boe Tissue Osteo q Caaliculi coect lacuae, formig a system of itercoected caals Providig routes for utriets ad oxyge to reach the osteocytes q The orgaizatio of osteos chages i respose to the physical demads placed o the skeleto

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15 Histology of Boe Tissue Spogy Boe q Lacks osteos q Lamellae are arraged i a lattice of thi colums called trabeculae Spaces betwee the trabeculae make boes lighter Trabeculae of spogy boe support ad protect the red boe marrow Hemopoiesis (blood cell productio) occurs i spogy boe

16 Histology of Boe Tissue Spogy Boe q Withi each trabecula are lacuae that cotai osteocytes q Osteocytes are ourished from the blood circulatig through the trabeculae q Iterior boe tissue is made up primarily of spogy boe q The trabeculae of spogy boe are orieted alog lies of stress helps boes resist stresses without breakig

17 Blood ad Nerve Supply of Boe Boe is richly supplied with blood q Periosteal arteries accompaied by erves supply the periosteum ad compact boe q Epiphyseal veis carry blood away from log boes Nerves accompay the blood vessels that supply boes q The periosteum is rich i sesory erves sesitive to tearig or tesio

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19 Boe Formatio The process by which boe forms is called ossificatio Boe formatio occurs i four situatios: q 1) Formatio of boe i a embryo q 2) Growth of boes util adulthood q 3) Remodelig of boe q 4) Repair of fractures

20 Boe Formatio Formatio of Boe i a Embryo q Cartilage formatio ad ossificatio occurs durig the sixth week of embryoic developmet

21 Flat boe of skull Blood capillary Ossificatio ceter Mesechymal cell Osteoblast Madible Collage fiber 1 Developmet of ossificatio ceter Osteocyte i lacua Caaliculus Osteoblast Newly calcified boe matrix Mesechyme codeses Blood vessel Spogy boe trabeculae Osteoblast 2 Calcificatio 3 Formatio of trabeculae Periosteum Spogy boe tissue Compact boe tissue 4 Developmet of the periosteum

22 Boe Formatio Formatio of Boe i a Embryo q Boe formatio follows oe of two patters Itramembraous ossificatio q Flat boes of the skull ad madible are formed i this way q Soft spots that help the fetal skull pass through the birth caal later become ossified formig the skull Edochodral ossificatio q The replacemet of cartilage by boe q Most boes of the body are formed i this way icludig log boes

23 Perichodrium Proximal epiphysis Diaphysis Distal epiphysis Hyalie cartilage Ucalcified matrix Calcified matrix Nutriet artery Periosteum Primary ossificatio ceter Spogy boe Ucalcified matrix Calcified matrix Periosteum (coverig compact boe) Medullary cavity Nutriet artery ad vei 1 Developmet of cartilage model 2 Growth of 3 Developmet of 4 cartilage model primary ossificatio ceter Developmet of the medullary cavity Secodary ossificatio ceter Epiphyseal artery ad vei Ucalcified matrix Articular cartilage Spogy boe Epiphyseal plate Nutriet artery ad vei 5 Developmet of secodary 6 ossificatio ceter Formatio of articular cartilage ad epiphyseal plate

24 Boe Growth Durig Ifacy, Childhood ad Adolescece Growth i Legth The growth i legth of log boes ivolves two major evets: q 1) Growth of cartilage o the epiphyseal plate q 2) Replacemet of cartilage by boe tissue i the epiphyseal plate

25 Boe Growth Durig Ifacy, Childhood ad Adolescece Osteoclasts dissolve the calcified cartilage, ad osteoblasts ivade the area layig dow boe matrix The activity of the epiphyseal plate is the way boe ca icrease i legth At adulthood, the epiphyseal plates close ad boe replaces all the cartilage leavig a boy structure called the epiphyseal lie

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27 Boe Growth Durig Ifacy, Childhood ad Adolescece Growth i Thickess q Boes grow i thickess at the outer surface Remodelig of Boe q Boe forms before birth ad cotiually reews itself q The ogoig replacemet of old boe tissue by ew boe tissue q Old boe is cotiually destroyed ad ew boe is formed i its place throughout a idividual s life

28 Boe Growth Durig Ifacy, Childhood ad Adolescece A balace must exist betwee the actios of osteoclasts ad osteoblasts q If too much ew tissue is formed, the boes become abormally thick ad heavy q Excessive loss of calcium weakes the boes, as occurs i osteoporosis q Or they may become too flexible, as i rickets ad osteomalacia

29 Factors Affectig Boe Growth ad Boe Remodelig Normal boe metabolism depeds o several factors Mierals q Large amouts of calcium ad phosphorus ad smaller amouts of magesium, fluoride, ad magaese are required for boe growth ad remodelig Vitamis q Vitami A stimulates activity of osteoblasts q Vitami C is eeded for sythesis of collage q Vitami D helps build boe by icreasig the absorptio of calcium from foods i the gastroitestial tract ito the blood q Vitamis K ad B12 are also eeded for sythesis of boe proteis

30 Factors Affectig Boe Growth ad Boe Remodelig Hormoes q Durig childhood, the hormoes most importat to boe growth are growth factors (IGFs), produced by the liver IGFs stimulate osteoblasts, promote cell divisio at the epiphyseal plate, ad ehace protei sythesis q Thyroid hormoes also promote boe growth by stimulatig osteoblasts q Isuli promotes boe growth by icreasig the sythesis of boe proteis

31 Factors Affectig Boe Growth ad Boe Remodelig Hormoes q Estroge ad testosteroe cause a dramatic effect o boe growth Cause of the sudde growth spurt that occurs durig the teeage year Promote chages i females, such as wideig of the pelvis Shut dow growth at epiphyseal plates q Parathyroid hormoe, calcitriol, ad calcitoi are other hormoes that ca affect boe remodelig

32 Fracture ad Repair of Boe Fracture Types q Ope (compoud) fracture q q q q q q q The broke eds of the boe protrude through the ski Closed (simple) fracture Does ot break the ski Commiuted fracture The boe is splitered, crushed, or broke ito pieces Greestick fracture A partial fracture i which oe side of the boe is broke ad the other side beds Impacted fracture Oe ed of the fractured boe is forcefully drive ito aother Pott s fracture Fracture of the fibula, with ijury of the tibial articulatio Colles fracture A fracture of the radius i which the distal fragmet is displaced Stress fracture A series of microscopic fissures i boe

33 Fracture ad Repair of Boe

34 Fracture ad Repair of Boe Calcium ad phosphorus eeded to stregthe ad harde ew boe after a fracture are deposited oly gradually ad may take several moths The repair of a boe fracture ivolves the followig steps q q q q 1) Formatio of fracture hematoma Blood leaks from the tor eds of blood vessels, a clotted mass of blood forms aroud the site of the fracture 2) Fibrocartilagious callus formatio Fibroblasts ivade the fracture site ad produce collage fibers bridgig the broke eds of the boe 3) Boy callus formatio Osteoblasts begi to produce spogy boe trabeculae joiig portios of the origial boe fragmets 4) Boe remodelig Compact boe replaces spogy boe

35 Fracture ad Repair of Boe

36 Osteo Periosteum Compact boe Spogy boe Fracture hematoma Blood vessel Phagocyte Fracture hematoma Red blood cell Boe fragmet Osteocyte Fibroblast Phagocyte Fibrocartilagious callus Osteoblast Collage fiber Chodroblast Cartilage 1 Formatio of fracture hematoma 2 Fibrocartilagious callus formatio Boy callus Osteoblast Spogy boe New compact boe Osteoclast Osteocyte 3 Boy callus formatio 4 Boe remodelig

37 Boe s Role i Calcium Homeostasis Boe is the body s major calcium reservoir Levels of calcium i the blood are maitaied by cotrollig the rates of calcium resorptio from boe ito blood ad of calcium depositio from blood ito boe q Both erve ad muscle cells deped o calcium ios (Ca 2+ ) to fuctio properly q Blood clottig also requires Ca 2+ q May ezymes require Ca 2+ as a cofactor

38 Boe s Role i Calcium Homeostasis Actios that help elevate blood Ca 2+ level q Parathyroid hormoe (PTH) regulates Ca 2+ exchage betwee blood ad boe tissue PTH icreases the umber ad activity of osteoclasts PTH acts o the kideys to decrease loss of Ca 2+ i the urie PTH stimulates formatio of calcitriol a hormoe that promotes absorptio of calcium from foods i the gastroitestial tract

39 Boe s Role i Calcium Homeostasis

40 Boe s Role i Calcium Homeostasis Actios that work to decrease blood Ca 2+ level q The thyroid glad secretes calcitoi (CT) which ihibits activity of osteoclasts q The result is that CT promotes boe formatio ad decreases blood Ca 2+ level

41 Exercise ad Boe Tissue Boe tissue alters its stregth i respose to chages i mechaical stress q Uder stress, boe tissue becomes stroger through depositio of mieral salts ad productio of collage fibers by osteoblasts q Ustressed boes dimiishes because of the loss of boe mierals ad decreased umbers of collage fibers The mai mechaical stresses o boe are those that result from the pull of skeletal muscles ad the pull of gravity Weight-bearig activities help build ad retai boe mass

42 Agig ad Boe Tissue The level of sex hormoes dimiishes durig middle age, especially i wome after meopause q A decrease i boe mass occurs q Boe resorptio by osteoclasts outpaces boe depositio by osteoblasts Female boes geerally are smaller ad less massive tha males q Loss of boe mass i old age has a greater adverse effect i females

43 Agig ad Boe Tissue There are two pricipal effects of agig o boe tissue: q q 1) Loss of boe mass Results from the loss of calcium from boe matrix The loss of calcium from boes is oe of the symptoms i osteoporosis 2) Brittleess Results from a decreased rate of protei sythesis Collage fibers gives boe its tesile stregth The loss of tesile stregth causes the boes to become very brittle ad susceptible to fracture