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78 Cards in this Set
- Front
- Back
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Osteology
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Is the study of bone |
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Skeletal System |
•Composed of bones, cartilages, and ligaments |
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Cartilage
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—Forerunnerof most bones •Coversmany joint surfaces of mature bone |
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Ligaments
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—Holdbones together at joints |
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Tendons
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—Attach muscle to bone (part of muscular system) |
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Living skeleton
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•Is made of dynamic tissues, full of cells, permeated with nerves and blood vessels •Continually remodels itself and interacts with other organ systems of the body |
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Bones and Teeth
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•Are the mostdurable remains of a once-living body |
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Functions of the Skeleton
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•Support
•Protection •Movement •Electrolytebalance •Acid–basebalance •Bloodformation |
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Support
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—limb bones and vertebrae supportbody; jaw bones support teeth; some bones support viscera |
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Protection
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—of brain, spinal cord, heart,lungs, and more |
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Movement
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—limb movements, breathing, andother movements depend on bone |
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Electrolytebalance
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—calcium and phosphate levels |
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Acid–basebalance
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—buffers blood against large pHchanges by altering phosphate and carbonate salt levels |
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Bloodformation
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—red bone marrow is the chiefproducer of blood cells |
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Bone (osseoustissue)
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—connective tissue with the matrixhardened by calcium phosphate and other minerals |
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Mineralizationor Calcification
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—the hardening process of bone |
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Individualbones (organs)
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•Consist of bone tissue, bone marrow, cartilage, adipose tissue,nervous tissue, and fibrous connective tissue |
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Flatbones
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–Thin, curved plates
–Protect soft organs –Clavicle, Scapula, Ribs and Hip Bones (pelvis) –Intramembranous Ossification |
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Longbones
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–Longer than wide –Rigid levers acted upon by muscles;crucial for movement –Endochondral Ossification |
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Shortbones
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–Approximately equal in length andwidth –Glide across one another inmultiple directions |
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Irregularbones
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–Elaborate shapes that do not fitinto other categories |
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Compactbone
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—dense outer shell of bone |
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Spongy(cancellous) bone
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—looselyorganized bone tissue –Found in center of ends and centerof shafts of long bones and in middle of nearly all others–Covered by more durable compactbone |
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Skeleton Make Up
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•3/4 compact and 1/4 spongy bone by weight |
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Longbone features
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–Diaphysis—shaftthat provides leverage•Medullary cavity (marrow cavity)—spacein the diaphysis of a long bone that contains bone marrow –Epiphyses—enlargedends of a long bone•Strengthen joint and anchorligaments and tendons |
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Articularcartilage
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—layer of hyaline cartilage thatcovers joint surface; allows joint to move more freely |
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Nutrient Foramina
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—minute holes in bone surface thatallows blood vessels to penetrate |
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Periosteum
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—external sheath covering most ofbone –Outer fibrous layer ofcollagen •Some fibers continuous with tendons •Perforating fibers—penetrateinto bone matrix–Inner osteogeniclayerof bone-forming cells•Important to bone growth andhealing of fractures |
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Endosteum
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—thin layer of reticular connectivetissue lining marrow cavity –Has cells that dissolve osseoustissue and others that deposit it |
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Epiphysealplate (growth plate)
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—areaof hyaline cartilage that separates epiphyses and diaphyses of children’s bones
–Enables growth in length –Epiphyseal line—inadults, a bony scar that marks where growth plate used to be |
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Fourprincipal types ofbone cells
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-Osteogenic cells
-Osteoblasts -Osteocytes -Osteoclasts |
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Osteogeniccells
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•Stem cells found in endosteum andinner layer of periosteum
–Arise from embryonic mesenchymalcells –Multiply continuously and give riseto most other bone cell types |
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Osteoblasts
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•Bone-forming cells; nonmitotic –Form single layer of cells underendosteum and periosteum –Synthesize soft organic matter ofmatrix which then hardens by mineral deposition –Stress stimulates osteogenic cellsto multiply rapidly and increase the number of osteoblasts which reinforce bone –Secrete hormone osteocalcin •Stimulates insulin secretion ofpancreas •Increases insulin sensitivity inadipocytes which limits the growth of adipose tissue |
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Osteocytes
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•Former osteoblasts that havebecome trapped in the matrix they deposited lacunae –Canaliculi—littlechannels that connect lacunae –Cytoplasmicprocesses of osteocytes reach into canaliculi and contact processes ofneighboring cells •Gapjunctions allow for passage of nutrients, wastes, signals –Someosteocytes reabsorb bone matrix while others deposit it –Actas strain sensors—when stressed, produce biochemical signals that regulate boneremodeling (shape and density changes that are adaptive) |
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Lacunae
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—tinycavities where osteocytes reside |
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Osteoclasts
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•Bone-dissolving cells found onbone surface –Develop from same bonemarrow stem cells that give rise to blood cells (different origin from otherbone cells) –Very large cells formed from fusionof several stem cells •Have multiple nuclei in each cell –Ruffled border (largesurface area) faces bone –Cells often reside in resorptionbays (pitsin bone surface) –Dissolving bone is part of boneremodeling |
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Matrixof Osseous Tissue
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•Is,by dry weight, about 1/3 organic and 2/3 inorganic matter |
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Organicmatter
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•Synthesized by osteoblasts –Collagen, carbohydrate–proteincomplexes, such as glycosaminoglycans,proteoglycans, and glycoproteins |
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Inorganicmatter
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•85% hydroxyapatite (crystallizedcalcium phosphate salt) –10% calcium carbonate –Other minerals (fluoride, sodium,potassium, magnesium) |
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Bone is a Composite Material Of
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•A combination of a ceramic and apolymer –Hydroxyapatite and other mineralsare the ceramic and collagen (protein) is the polymer |
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Ceramic
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–Portion allows the bone tosupport body weight without sagging •Rickets is a disease caused bymineral deficiency and resulting in soft, deformed bones |
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Polymer
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–(protein) gives someflexibility •Osteogenesis imperfecta (brittlebone disease) results from a defect in collagen deposition |
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Histology of compact bone
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•Reveals osteons (haversian systems) –Concentriclamellae surrounda central(haversian)canal runninglongitudinally –Perforating(Volkmann) canals—transverse or diagonal passages –Circumferentiallamellae fillouter region of dense bone –Interstitiallamellae fillirregular regions between osteons |
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Spongy Bone Consists Of
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-Latticeof bone covered with endosteum •Sliversof bone called spicules •Thinplates of bone called trabeculae –Spacesfilled with redbone marrow –Few osteons and no central canals •Allosteocytes close to bone marrow –Provides strength with minimalweight •Trabeculaedevelop along bone’s lines of stress |
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Bone marrow
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•Soft tissue occupying marrowcavities of long bones and small spaces of spongy bone |
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Red marrow (myeloidtissue)
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•Containshemopoietictissue—producesblood cells –Innearly every bone in a child –Inadults, found in skull, vertebrae, ribs, sternum, part of pelvic girdle, andproximal heads of humerusand femur |
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Yellow marrow
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•Found in adults –Fattymarrow that does not produce blood–Cantransform back to red marrow in the event of chronic anemia |
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Ossification orosteogenesis
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•The formation of bone •In the human fetus and infant, bonedevelops by two methods –Intramembranous ossification –Endochondral ossification |
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Intramembranousossification |
•Producesflat bones of skull and clavicle in fetus•Thickenslong bones throughout life
•Note the periosteum and osteoblasts 1) Osteogenitor Stem Cells 2) Osteoblasts deposit matrix (build bone) 3) Osteocytes trapped in matrix 4) Osteoclasts dissolve and remodel |
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EndochondralOssification
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•Bone develops from a hyalinecartilage model or template •Process starts around 6th week of development &continues into early 20’s •Most of the bones of skeletondevelop this way:–Vertebrae,ribs, sternum, bones of limbs (long bones) •By late teens to early 20s, allremaining cartilage in the epiphyseal plate is generally consumed –Gapbetween epiphyses and diaphysis closes –Primaryand secondary marrow cavities unite into a single cavity–Bonecan no longer grow in length |
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BoneGrowth and Remodeling
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•Ossification continues throughout life with thegrowth and remodeling of bones •Bones grow in two directions –Length –Width |
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BoneElongation
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•Epiphyseal plate—cartilage transitions to bone –Functionsas growthzone wherebone elongates –Hastypical hyaline cartilage in the middle with transition zones on each sidewhere cartilage is replaced by bone –Metaphysisiszone of transition facing the marrow cavity •Thisis interstitial growth—growth from within –Is a result ofcartilage growth within the epiphyseal plate –Epiphyses close when cartilage isgone—epiphyseallineof spongy bone marks site of former epiphyseal plate •Lengthwise growth is finished •Occurs at different ages indifferent bones |
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Achondroplastic dwarfism
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•Long bones stop growing inchildhood •Normal torso, short limbs –Failure of cartilage growth inmetaphysis–Spontaneous mutation producesmutant dominant allele |
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Pituitarydwarfism
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•Lack of growth hormone –Normal proportions with shortstature |
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Appositionalgrowth
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•Occurs at bone surface –Continual growth in diameter andthickness –Intramembranous ossification –Osteoblasts of inner periosteumdeposit osteoid tissue •Become trapped as tissue calcifies –Lay down matrix in layers parallelto surface •Forms circumferentiallamellae •Osteoclasts of endosteum enlargemarrow cavity |
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Boneremodeling
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• (absorption and deposition) occursthroughout life—10% of skeleton per year –Repairs microfractures,releases minerals into blood, reshapes bones in response to use and disuse –Wolff’s law of bone: architectureof bone determined by mechanical stresses placed on it •Remodeling is a collaborative andprecise action of osteoblasts and osteoclasts •Bony processes grow larger inresponse to mechanical stress |
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Physiologyof Osseous Tissue
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•A mature bone remains ametabolically active organ –Involvedin its own maintenance of growth and remodeling –Exertsa profound influence over the rest of the body by exchanging minerals withtissue fluid •Disturbanceof calciumhomeostasis inskeleton disrupts function of other organ systems –Especiallynervous and muscular |
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Mineral deposition (mineralization)
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•Process in which calcium,phosphate, and other ions are taken from blood and deposited in bone –Osteoblastsproduce collagen fibers that spiral the length of the osteon–Fibersbecome encrusted with minerals •Hydroxyapatitecrystals form at solubility product—criticallevel of calcium times phosphate concentration •Firstfew crystals act as seed crystalsthat attract more calcium and phosphate from solution |
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Abnormalcalcification (ectopic ossification)
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—Formation of a calculus(calcified mass) in an otherwise soft organ such as alung,brain, eye, muscle, tendon, or artery (arteriosclerosis)
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Mineral Resorption(demineralization)
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•Process of dissolving bone andreleasing minerals into blood –Performedby osteoclastsat ruffledborder –Hydrogenpumps inmembranes secrete hydrogen into space between osteoclast and bone surface –Chlorideions followby electrical attraction –Hydrochloricacid (pH4) dissolves bone minerals –Acidphosphatase enzymedigests collagen |
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Orthodontic appliances (braces)
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•Reposition teeth through resorption and deposit –Toothmoves because osteoclasts dissolve bone ahead of tooth;osteoblasts deposit bone behind the tooth |
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Calcium Homeostasis
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•Depends on a balance betweendietary intake, urinary and fecal losses, and exchanges between osseous tissue •Calcium homeostasis is regulated bythree hormones: –Calcitriol, Calcitonin, and Parathyroid Hormone •Calcium needs to be 9 to 10mG/dL |
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Hypocalcemia
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•Deficientcalcium in blood –Changesmembrane potentials and causes overly excitable nervous system and tetany(muscle spasms) –Pregnancyand lactation increase risk of this. –Causedby vitamin D deficiency, diarrhea, thyroid tumors, underactive parathyroidglands •Laryngospasmcan cause suffocation |
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Hypercalcemia
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•Excessivecalcium levels
–Makesion channels less responsive and thus nerve and muscle are less excitable •Can cause emotional disturbance,muscle weakness, sluggish reflexes, cardiac arrest –Rarely occurs |
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CalciumHomeostasis
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•Calciumand phosphate are used for much more than bone structure•Phosphateis a component of DNA, RNA, ATP, phospholipids, and pH buffers •Calciumneeded in neuron communication, muscle contraction, blood clotting, andexocytosis •Mineralsare deposited in the skeleton and withdrawn when they are needed for otherpurposes |
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Calcitrol (Vitamin D) |
- Produced by skin - Mature in Liver/Kidney - Increase intestinal absorption of calcium |
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Calcitonin |
- Decrease in blood calcium - Sent to bone to strengthen --> osteoblasts |
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Parathyroid Hormone |
- Increase blood calcium - Remove calcium in bone --> osteoclasts |
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OtherFactors Affecting Bone
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•Atleast 20 or more hormones, vitamins, and growth factors affect osseous tissue •Bonegrowth especially rapid in puberty and adolescence –Girls grow faster than boys andreach full height earlier •Estrogen has stronger effect thantestosterone on bone growth –Males grow for a longer time andalso taller |
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Anabolicsteroids
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•Cause growth to stop
–Epiphyseal plate “closes”prematurely –Results in abnormally short adultstature |
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Orthopedics
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•Branch of medicine dealing withprevention and correction of injuries and disorders of bones, joints, andmuscles –Nameimplies its origin as field treating skeletal deformities in children •Includes the design of artificialjoints and limbs and the treatment of athletic injuries |
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Causes ofFractures |
•Stress — abnormal trauma toa bone (a fall) •Pathological —bone weakened bydisease (such as bone cancer or osteoporosis --which means decreased bone mass, increased demineralization and brittle bones increase risk) |
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Types of Fractures (breaks) |
•Non-displaced -- broken but still in alignment •Displaced -- broken and misalignment •Comminuted -- broken in 3 or more pieces •Greenstick -- bone is bent and incompletely broken. |
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Treatment of Fractures
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•Closedreduction—procedure in which bone fragmentsare manipulated into their normal positions without surgery
•Openreduction—involves surgical exposure of thebone and the use of plates, screws, or pins to realign the fragments •Cast—normally used to stabilize andimmobilize healing bone |
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Healing of Fractures
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-- Hematoma/granulation -- Soft Callus -- Hard Callus -- Remodeling |
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Additional Treatments of Fractures
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•Fracturesof the femur in children often treated with traction –Aligns bone fragments by overridingforce of the strong thigh muscles•Hipfractures in older adults are usually pinned and early walking is encouraged –Fractures taking more than 2 monthsto heal may be treated with electrical stimulation which suppresses effects ofparathyroid hormone |
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Osteoporosis
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•Estrogenmaintains bone density in both sexes; inhibits resorption by osteoclasts
•Postmenopausalwhite women at greatest risk –Ovaries cease to secrete estrogen –White women begin to lose bone massas early as age 35 •By age 70, average loss is 30% ofbone mass –Risk factors: race, age, gender,smoking, diabetes mellitus, diets which are poor in: calcium, protein, vitaminsC and D •Also seen in young female athletes with low body fat causing them to stopovulating and decrease estrogen secretion |
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Treatments for Osteoporosis |
–Estrogen replacement therapy (ERT) slowsbone resorption, but increases risk of breast cancer, stroke, and heart disease –Drugs Fosamax,Actonel destroyosteoclasts –PTH slows bone loss if given as dailyinjection •Forteo(PTH derivative) increases density by 10% in 1 year–May promote bone cancer so use islimited to 2 years –Best treatment is prevention:exercise and a good bone-building diet between ages 25 and 40 |
