EXSC%223:%Week%of%10/3/16%!Textbook%notes%Ch.%6.4%6.4!The!gross!structure!of!all!bones!consists!of!compact!bone!sandwiching!spongy!bone!• Gross!anatomy!o Compact!and!spongy!bone!§ External!layer:!compact!• Looks!smooth!and!solid!to!the!naked!eye!§ Internal!layer:!spongy!• Looks!like!a!honeycomb!• Made!up!of!small!flat!pieces!called!trabeculae!• Space!between!trabeculae!is!filled!with!red!or!yellow!bone!marrow!o Short,!irregular,!and!flat!bones!§ Share!a!general!structure:!thin!plates!of!spongy!bone!covered!by!compact!bone!§ The!compact!bone!is!covered!by!connective!tissue!membranes!• The!outside!is!covered!by!the!periosteum!• The!inside!is!covered!by!the!endosteum!§ Contain!bone!marrow!between!the!trabeculae!but!do!not!have!a!well-defined!marrow!cavity!o Long!bone!§ General!structure:!shaft,!bone!ends,!and!membranes!§ Diaphysis!• Tubular!shaft!that!forms!the!long!axis!of!the!bone!• Constructed!of!a!thick!collar!of!compact!bone!that!surrounds!a!central!medullary!cavity!(marrow!cavity)!o In!adults:!medullary!cavity!is!filled!with!fat!(yellow!marrow)!§ Epiphyses!• Bone!ends!• Usually!broader!than!the!diaphysis!• Outer!shell:!compact!bone!• Inner:!spongy!bone!• Thin!layer!of!hyaline!cartilage!(articular)!covers!the!joint!surface!of!each!epiphysis!• Epiphyseal!line!divides!the!epiphyses!from!diaphysis!o Remnant!of!the!epiphyseal!plate:!a!disc!of!hyaline!cartilage!that!grows!during!childhood!to!lengthen!the!bone!§ Membranes!• Periosteum!o White,!double-layered!membrane!o Covers!external!surface!of!entire!bone!except!joint!surfaces!o Outer!layer!§ Fibrous!§ Dense!irregular!connective!tissue!o Inner!layer!§ Osteogenic!§ Consists!mostly!of!osteogenic!cells!(cells!that!give!rise!to!all!bone!cells!except!osteoclasts)!o Richly!supplied!with!nerve!fibers!and!blood!vessels!o Perforating!(Sharpey’s)!fibers:!collagen!fibers!that!secure!the!periosteum!to!the!underlying!bone!• Endosteum!o Delicate!connective!tissue!o Covers!internal!bone!surfaces!o Cover!the!trabeculae!of!spongy!bones!and!lines!the!canals!that!pass!through!compact!bone!o Contains!osteogenic!cells!o Hematopoietic!tissue!in!bones!§ Red!marrow!§ Found!in!trabecular!cavities!of!spongy!bone!• Called!red!marrow!cavities!§ In!infants:!medullary!cavity!and!all!spongy!bone!has!red!bone!marrow!§ In!adults:!yellow!marrow!extends!into!epiphyses!and!little!red!marrow!is!in!spongy!bone!cavities!o Bone!markings!§ External!surfaces!of!bones!have!bone!markings!• projections,!depressions,!and!openings!• sites!of!muscle,!ligament,!and!tendon!attachment,!joint!surfaces,!conduits!for!blood!vessels!and!nerves!§ projections!• markings!that!bulge!outward!from!surface!o heads,!trochanters,!spines,!etc!o normally!indicate!the!stresses!from!muscles!pulling!on!them!or!are!modified!surfaces!where!bones!meet!and!form!joints!§ depressions!and!openings!• fossae,!sinuses,!foramina,!grooves!• allow!nerves!and!blood!vessels!to!pass!• Microscopic!anatomy!o 5!major!cell!types!§ osteogenic!cells!• mitotically!active!stem!cells!• located!in!the!periosteum!and!endosteum!• squamous!cells!• can!be!stimulated!to!become!osteoblasts!or!bone!lining!cells!§ osteoblasts!• bone-forming!cells!• secrete!bone!matrix!o collagen!o calcium-binding!proteins!• actively!mitotic!§ osteocytes!• mature!bone!cells!that!occupy!lacunae!• monitor!and!maintain!bone!matrix!• stress!sensors!and!respond!to!mechanical!stimuli!• if!they!die,!the!surrounding!matrix!is!resorbed!§ bone!lining!cells!• flat!cells!• found!on!bone!surfaces!where!remodeling!is!not!going!on!• help!maintain!matrix!§ osteoclasts!• giant!multinucleate!cells!• located!at!sites!of!bone!resorption!• function:!break!down!(resorb)!bone!o compact!bone!§ osteon!(Haversian!System):!structural!unit!of!compact!bone!• elongated!cylinder!oriented!parallel!to!the!long!axis!of!the!bone!• function:!weight!bearing!pillars!• group!of!hollow!tubes!of!bone!matrix!placed!in!concentric!rings!like!tree!trunk!rings!o each!“tree!ring”!is!a!lamella!o collagen!fibers!in!a!lamella!run!in!the!same!direction!o collagen!fibers!in!adjacent!lamellae!run!in!opposite!directions!§ canals!• central!canal/Haversian!canal:!canal!running!through!the!core!of!each!osteon!o blood!vessels!and!nerves!run!through!it!• perforating!canal/Volkmann’s!canal:!!o lie!at!right!angles!to!long!axis!of!bone!o function:!connect!blood!and!nerve!supply!of!the!medullary!cavity!to!the!central!canals!o not!surrounded!by!lamellae!like!central!canals!§ lined!with!endosteum!• canaliculi!o hairlike!canals!o connect!lacunae!to!each!other!and!central!canal!§ interstitial!and!circumferential!lamellae!• interstitial!lamellae:!incomplete!lamellae!o located!between!intact!osteons!o fill!the!gaps!between!forming!osteons!or!remnants!of!osteons!• circumferential!lamellae!o located!just!deep!to!the!periosteum!and!just!superficial!to!the!endosteum!o extend!around!the!entire!circumference!of!the!diaphysis!o resist!twisting!of!the!long!bone!o spongy!bone!§ looks!poorly!organized!§ trabeculae!!• only!a!few!cells!thick!• align!along!lines!of!stress!to!help!bone!resist!stress!• contain!irregularly!arranged!lamellae!and!osteocytes!connected!by!canaliculi!• no!osteons!present!• Chemical!composition!of!bone!o Organic!components!§ Cells!• Osteogenic!cells!• Osteoblasts!• Osteocytes!• Bone-lining!cells!• Osteoclasts!§ Osteoid:!organic!part!of!the!matrix!• Makes!up!1/3!of!the!matrix!• Includes!ground!substance!and!collagen!fibers!o Secreted!by!osteoblasts!o Inorganic!components!§ Hydroxyapatites!(mineral!salts)!• Calcium!phosphates!o Tiny,!needlelike!crystals!o Makes!bone!hard!!Lecture%notes%10/3%%Long!bone!structure!• Consists!of!1!diaphysis!and!2!epiphyses!o Most!of!diaphysis!(shaft)!is!compact,!only!the!ends!have!spongy!bone!o Diaphysis!capped!by!epiphyses!o Epiphyses!have!spongy!bone!encased!by!compact!bone!• Diaphysis!o Tubular!shaft!that!forms!the!axis!of!long!bones!• Epiphyses!o Expanded!ends!of!long!bones!o Epiphyseal!line!§ Called!this!when!someone!is!done!growing!§ Remnants!of!growth!plate!§ Like!a!scar!o Epiphyseal!plate!§ Called!this!when!someone!is!still!growing!• bones!are!surrounded!by!membranes!or!cartilage!o diaphysis:!covered!by!membrane!§ 2!membrane!layers!§
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