Presentation on theme: "Chapter 7 Lecture Outline"— Presentation transcript:
1 Chapter 7 Lecture Outline See PowerPoint Image Slidesfor all figures and tables pre-inserted intoPowerPoint without notes.Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2 Bone as a TissueConnective tissue with a matrix hardened by minerals (calcium phosphate)Individual bones consist of bone tissue, marrow, blood, cartilage and periosteumContinually remodels itselfFunctions of the skeletal systemsupport, protection, movement, electrolyte balances, acid-base balance and blood formation
3 I. Components and Functions of the Skeletal System A. SupportB. ProtectionC. Movement FacilitationD. Mineral StorageE. Blood Cell ProductionF. Energy Storage
4 II. Macroscopic Structure of Bones A. Two types of bone1. compact- dense white osseous tissue2. spongy- more loosely organized form of osseous tissueWe will discuss differences between compact and spongy boneWhere locatedMicroscopic anatomy
5 B. Parts of a Long Bone 1. diaphysis 2. epiphysis 3. articular surfaces4. periosteum5. endosteum
6 General Features of Bones 1. Shaft (diaphysis) = cylinder of compact bonemarrow cavity (medullary cavity) lined with endosteum (osteogenic cells and reticular connective tissue)2. Enlarged ends (epiphyses)spongy bone covered by compact boneenlarged to strengthen joint and attach ligaments3. Joint surface covered with articular cartilage4. Shaft covered with periosteum (sheath)outer fibrous layer of collageninner osteogenic layer of bone forming cells5. Endosteum-lines the internal surface of the bone
7 Structure of a Long Bone Compact and spongy boneMarrow cavityArticular cartilagePeriosteumEpiphyseal plate=growth plate
8 Structure of a Flat Bone External and internal surfaces composed of compact boneMiddle layer is spongy bone and bone marrowSkull fracture may leave inner layer of compact bone unharmed
9 D. Bone Cells 1. Osteogenic cells 2. Osteoblasts 3. Osteocytes 4. Osteoclasts
10 Cells of Osseous Tissue (1) Osteogenic cells in endosteum, periosteum or central canals give rise to new osteoblastsarise from embryonic fibroblastsmultiply continuouslyOsteoblasts mineralize organic matter of matrixOsteocytes are osteoblasts trapped in the matrix they formedcells in lacunae connected by gap junctions inside canaliculi
11 Cells of Osseous Tissue (2) Osteoclasts develop in bone marrow by fusion of 3-50 stem cellsReside in pits that they ate into the bone
12 A. Bone MatrixMatrix is 25% water, 25% proteins (mostly collagen), 50% calcium saltsCalcium salts: mostly hydroxyapatite(Ca10(PO4)6(OH)2Combination provides for strength and resilienceminerals resist compression; collagen resists tensionbone adapts by varying proportions
14 B. Compact BoneOsteon = basic structural unit= haversian systemcentral canal =osteonic canal=haversian canal and its lamellae (cylinders formed from layers)osteocytes connected to each other and their blood supply by tiny cell processes in canaliculiPerforating canals or Volkmann canalsvascular canals perpendicularly joining central canals
15 B. Compact Bone Haversian canals Volkmann canals (perforating canals) Osteon = basic structural unit= haversian systemTwo types of vascular channelsHaversian canalsVolkmann canals (perforating canals)vascular canals perpendicularly joining central canalsNot all of the matrix organized into osteonsInner and outer boundaries of dense bone are organized in circumferential lamellae, run parallel to bone surface
17 C. Spongy BoneSpongelike appearance formed by plates of bone called trabeculaespaces filled with red bone marrowno osteocyte is far from blood of bone marrowProvides strength with little weighttrabeculae develop along bone’s lines of stress
19 Bone MarrowIn medullary cavity (long bone) and among trabeculae (spongy bone)Red marrow like thick bloodreticular fibers and immature cellsHemopoietic (produces blood cells)in vertebrae, ribs, sternum, pelvic girdle and proximal heads of femur and humerus in adultsYellow marrowfatty marrow of long bones in adultsGelatinous marrow of old ageyellow marrow replaced with reddish jelly
20 IV. Ossification B. Endochondral Ossification Replacement of other tissues with bonesA. Intramembranous Ossification -process that forms flat bones (skull, mandible)B. Endochondral Ossification-bones are formed from a hyaline cartilage model-bone tissue forms within the model-process that forms long and short bones
21 A. Intramembranous Ossification 1. mesenchyme (embryonic connective tissue)forms a richly vascularized layer with cell-to-cell contact2. collagen fibers are laid down randomlyforms a gel-like material3. mesenchymal cells differentiate into osteoblasts4. new osteoblasts continue to secrete and mineralize matrix5. trabeculae are formed (ossification centers)becomes middle of bone6. vascular mesenchyme condenses to form peri- and endosteum
22 A. Intramembranous Ossification 7. red bone marrow invades spaces between trabeculaenew periosteum develops osteoblasts-these form trabeculae which grow together to form compact bone on outer surface
23 Intramembranous Ossification 1 Produces flat bones of skull and clavicle.
24 Intramembranous Ossification 2 Note the periosteum and osteoblasts.
25 B. Endochondral Ossification 1. Mesenchyme condenses in shape of future boneDifferentiate into chondroblastsDevelops perichondrium2. Model grows as chondroblasts divideChondroblasts hypertrophy and dieMatrix becomes calcified3. Perichondrium converts to periosteumForms a thin periosteal collar in mid-diaphysis4. Blood vessels invade modelCarries osteoblasts, osteoclasts, and red marrow to interior of model
26 B. Endochondral Ossification 5. Interior osteoclasts break down calcified cartilage matrixInterior osteoblasts produce bone matrix of trabeculae, this is primary ossification center6. Similar events begin to occur in each epiphysisThese are secondary ossification centers7. As primary ossification center enlarges, early trabeculae are removed to form medullary cavitiyThis becomes populated with red marrow
31 V. Bone Growth and Remodeling A. Interstitial growthGrowth in length of bones1. zone of cell proliferation2. zone of cell hypertrophy3. zone of calcification4. zone of bone depositionB. Appositional growthGrowth in diameterOccurs by subperiosteal intramembraneous ossification
32 RemodelingOccurs for four reasons1. bone growth in length and width2. changes in use of bone3. bone tissue turnover-internal remodeling4. plasma Ca2+ levels
33 V. Bone Growth and Remodeling Bones increase in lengthinterstitial growth of epiphyseal plateepiphyseal line is left behind when cartilage goneBones increase in width = appositional growthosteoblasts lay down matrix in layers on outer surface and osteoclasts dissolve bone on inner surfaceBones remodeled throughout lifeWolff’s law of bone = architecture of bone determined by mechanical stressesaction of osteoblasts and osteoclastsgreater density and mass of bone in athletes or manual worker is an adaptation to stress
34 Hormonal Regulation of Bone Growth and Replacement A. Growth HormoneB. Sex steroidsBone growth especially rapid in puberty and adolescence when surges of GH, estrogen, and testosterone promote ossificationC. Thyroid hormones increased GHD. Parathyroid hormonesE. CalcitriolF. Calcitonin
35 Ion Imbalances Changes in phosphate levels = little effect Changes in calcium can be serioushypocalcemia is deficiency of blood calciumcauses excitability of nervous system if too lowmuscle spasms, tremors or tetany ~6 mg/dLlaryngospasm and suffocation ~4 mg/dLwith less calcium, sodium channels open more easily, sodium enters cell and excites neuronhypercalcemia is excess of blood calciumbinding to cell surface makes sodium channels less likely to open, depressing nervous systemmuscle weakness and sluggish reflexes, cardiac arrest ~12 mg/dLCalcium phosphate homeostasis depends on calcitriol, calcitonin and PTH hormone regulation
36 Carpopedal SpasmHypocalcemia demonstrated by muscle spasm of hands and feet.
37 Hormonal Control of Calcium Balance Calcitriol, PTH and calcitonin maintain normal blood calcium concentration.
38 Calcitriol (Activated Vitamin D) Produced by the following processUV radiation and epidermal keratinocytes convert steroid derivative to cholecalciferol - D3liver converts it to calcidiolkidney converts that to calcitriol (vitamin D)Calcitriol behaves as a hormone that raises blood calcium concentrationincreases intestinal absorption and absorption from the skeletonincreases stem cell differentiation into osteoclastspromotes urinary reabsorption of calcium ionsAbnormal softness (rickets) in children and (osteomalacia) in adults without vitamin D
40 Calcitonin (tones down blood Ca2+ levels) Secreted (C cells of thyroid gland) when calcium concentration rises too highFunctionsreduces osteoclast activity as much as 70%increases the number and activity of osteoblastsImportant in children, little effect in adultsosteoclasts more active in childrendeficiency does not cause disease in adultsReduces bone loss in osteoporosis
42 Parathyroid Hormone (PTH) Glands on posterior surface of thyroidReleased with low calcium blood levelsFunction = raise calcium blood levelcauses osteoblasts to release osteoclast-stimulating factor (RANKL) increasing osteoclast populationpromotes calcium resorption by the kidneyspromotes calcitriol synthesis in the kidneysinhibits collagen synthesis and bone deposition by osteoblastsSporatic injection of low levels of PTH causes bone deposition
44 Other Factors Affecting Bone Hormones, vitamins and growth factorsGrowth rapid at pubertyhormones stimulate osteogenic cells, chondrocytes and matrix deposition in growth plategirls grow faster than boys and reach full height earlier (estrogen stronger effect)males grow for a longer time and tallerGrowth stops (epiphyseal plate “closes”)teenage use of anabolic steroids = premature closure of growth plate and short adult stature
45 Osteoporosis 1Bones lose mass and become brittle (loss of organic matrix and minerals)risk of fracture of hip, wrist and vertebral columncomplications (pneumonia and blood clotting)Postmenopausal white women at greatest riskby age 70, average loss is 30% of bone massblack women rarely suffer symptoms
46 Osteoporosis 2Estrogen maintains density in both sexes (inhibits resorption)testes and adrenals produce estrogen in menrapid loss after menopause, if body fat too low or with disuse during immobilizatonTreatmentERT slows bone resorption, but increases risk breast cancer, stroke and heart diseasePTH slows bone loss if given daily injectionForteo increases density by 10% in 1 yearmay promote bone cancerbest treatment is prevention -- exercise and calcium intake (1000 mg/day) between ages 25 and 40
48 VII. Effect of Exercise on Bone Increased exercise causes increased mechanical stress on boneStimulates remodeling and increased bone massStimulates release of calcitoninLack of exercise causes atrophy of bone