Week 7 Notes
Week 7 Notes EXSC 223
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This 14 page Class Notes was uploaded by Madison Waterman on Saturday October 8, 2016. The Class Notes belongs to EXSC 223 at University of South Carolina taught by Dr. Raymond Thompson in Fall 2016. Since its upload, it has received 26 views. For similar materials see Anatomy and Physiology I in Science at University of South Carolina.
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Date Created: 10/08/16
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 § periosteum: outer layer, thick, dense irregular connective tissue with layer of bone cells § endosteum: inner layer, thin o epiphysis: covered by cartilage § cartilage grew as bones grew to support more weight § articular cartilage stops growing when you stop growing • perforating (Sharpey’s) fibers: connect bone to periosteum and endosteum 4 types of bone cells 1. osteogenic cell: stem cell 2. osteoblast: responsible for bone growth 3. osteocyte: maintains bone matrix 4. osteoclast: bone-resorbing cell • not derived from osteogenic cells • derived from mesenchyme • antagonists to osteoblasts • break down (cleave) bone o function: raise blood calcium levels compact bone is made of osteons • osteon (Haversian system): structural unit of compact bone o made of concentric layers of collagen o only in compact bone not spongy bone o made of lamellae, central canals, and volkmann’s canals o interstitial lamellae are between osteocytes o canaliculi: spaces that osteocytes extend into for protection spongy bone • never found by itself in a healthy person • always encased in compact bone • short, irregular, and flat bones have compact and spongy • spongy bone also called diploe • made of trabeculae covered by endosteum • no diaphysis or epiphysis • contain bone marrow between trabeculae • trabeculae: mineralized collagen o relieve stress o trabeculae remodel based on how you stress the bone Wolf’s Law • bone changes based on mechanical stress or lack thereof Hematopoietic tissue (red marrow) found in the hollow space of bone • in infants o medullary cavity of diaphysis o all areas of spongy bone including epiphyses • in adults o trabeculae of flat bones and the head of the femur and humerus only o yellow marrow (adipose) in diaphysis of long bone chemical composition of bone • organic o collagen (protein) • inorganic o hydroxyapatites (mineral salts) § 65% of bone by mass § mainly calcium phosphates § responsible for bone hardness and its resistance to compression bone development • ossification=osteogenesis (actually different but used interchangeably) • embryo: formation of bony skeleton o membrane bone: intramembranous ossification o endochondral bone: endochondral ossification § start with cartilage and replace with bone • until adulthood: bone growth • adulthood: bone remodeling • intramembranous ossification 1. ossification center (cluster of osteoblasts) appears in fibrous connective tissue membrane 2. Bone matrix (osteoid) is secreted in the fibrous membrane 3. Woven bone and periosteum form a. Accumulating osteoid laid down between embryonic blood vessels=network of trabeculae b. Vascularized mesenchyme condenses on the external face of woven bone 4. Bone collar of compact bone forms and red marrow appears a. Trabeculae just deep to the periosteum thickens, forming a woven bone collar later replaced with mature lamellar bone b. Spongy bone: consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow • Endochondral ossification o Hyaline cartilage used as a template o Formation of bone collar around hyaline cartilage template Textbook notes Ch. 6.5-6.8 6.5 Bones develop either by intramembranous or endochondral ossification • Ossification: process of bone formation • Endochondral ossification: bone develops by REPLACING hyaline cartilage o Essentially all bones below the base of the skull (except for clavicles) form by endochondral ossification o Hyaline cartilage is used as a template but must be broken down as ossification proceeds o Process happens late in the 2 month of development for bone construction o Steps: 1. Blood vessels infiltrate the perichondrium covering the hyaline cartilage template to convert it to a vascularized periosteum 2. Mesenchymal cells specialize into osteoblasts 3. Osteoblasts secrete osteoid against the hyaline cartilage diaphysis to form a bone collar 4. Cartilage in the center of the diaphysis calcifies then develops cavities 5. The periosteal bud invades the internal cavities and spongy bone forms 6. The diaphysis elongates and medullary cavity forms 7. The epiphyses ossify o After, hyaline cartilage only exists at the epiphyseal plates and on the epiphyseal surfaces • Intramembranous ossification: a bone develops from a fibrous membrane o Forms the cranial bones and clavicles o Week 8: ossification begins within fibrous connective tissue membranes o Steps: 1. Ossification centers appear in the fibrous connective tissue membrane 2. Osteoid is secreted within the fibrous membrane and calcifies 3. Woven bone and periosteum form 4. Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Postnatal bone growth o Long bones lengthen by interstitial growth of the epiphyseal plate cartilage § Cartilage forms tall columns in the following zones: • Proliferation zone: cells facing the epiphysis divide quickly which pushes the epiphysis away from the diaphysis, thus lengthening the bone • Hypertrophic zone: older chondrocytes hypertrophy and their lacunae erode and enlarge • Calcification zone: surrounding cartilage matrix calcifies and these chondrocytes die and deteriorate • Ossification zone: new bone forms § During this growth, epiphyseal remodeling happens to maintain proportion between diaphysis and epiphyses § Longitudinal bone growth ends when the epiphyses and diaphysis bone fuses (epiphyseal plate closure) o All bones grow in thickness by appositional growth § Osteoblasts secrete bone matrix on the external bone surface § Osteoclasts remove bone § More building up than breaking down in order to produce thicker stronger bone without getting too heavy o Most bones stop growing but some facial bones continue to grow throughout life o Hormonal regulation of bone growth § Growth hormone • Stimulus for epiphyseal plate activity • Released by anterior pituitary gland § Thyroid hormones • Modulate the activity of growth hormone • Ensures the skeleton has proper proportions while growing § Sex hormones • At puberty they are released in increasing amounts • Promote the typical growth spurt • Control masculinization or feminization of some parts of the skeleton • Induce epiphyseal closure 6.6 Bone remodeling involves bone deposit and removal • 5-7% of bone mass recycled each week • spongy bone replaced every 3-4 years • compact bone replaced every 10 years • bones become more brittle with time because more calcium salts crystallize • bone remodeling= bone deposit and bone resorption • remodeling units coordinate bone remodeling o groups of adjacent osteoblasts and osteoclasts • bone deposit o osteoid seam: unmineralized band of bone matrix that marks the area of new matrix deposits o calcification front: abrupt transition between osteoid seam and older mineralized bone o precise trigger for calcification unknown § mechanical signals involved § local concentrations of calcium and phosphate ions are critical • bone resorption o carried out by osteoclasts o osteoclasts move along the bone surface digging depressions as they break down the bone matrix o they secrete protons and lysosomal enzymes to digest the organic matrix o the broken down products are endocytosed by the osteoclast, go through transcytosis, and released into the interstitial fluid then the blood • control of remodeling o regulated by genetic factors and two control loops (one hormonal, one mechanical) o hormonal controls § parathyroid hormone (PTH) • primary hormonal control • produced by the parathyroid glands § calcitonin • lesser influence than PTH • produced by parafollicular cells (C cells) § leptin • released by adipose tissue • regulates bone density § negative feedback system • when ionic calcium blood levels decline, PTH is released • increased PTH stimulates osteoclasts to resorb bone • this releases calcium into the blood • homeostasis restored o mechanical controls § bone’s response to mechanical stress and gravity § keeps the bones strong where stressors are acting § Wolff’s law: a bone grows or remodels in response to the demands placed on it 6.7 Bone repair involves hematoma and callus formation and remodeling • Bones are strong but may fracture (break) • Fractures classified by o Position of the bone ends after fracture § Nondisplaced: bone ends retain normal position § Displaced: bone ends out of normal alignment o Completeness of the break § Complete: bone is broken through § Incomplete: bone is not broken all the way through o Whether the bone ends penetrate the skin § Open/compound: bone penetrates the skin § Closed/simple: bone does not penetrate the skin • Fracture treatment o Reduction: realignment of the broken bone ends § Closed/external: physician’s hands move them into position § Open/internal: bone ends secured surgically with pins and wires o Then it is immobilized with a cast so it can heal o Steps of healing for a simple fracture: § A hematoma (mass of clotted blood) forms § Fibrocartilaginous callus forms § Bony callus forms § Bone remodeling 6.8 Bone disorders result from abnormal bone deposition and resorption • Osteomalacia: includes many disorders in which bones are poorly mineralized • Rickets: poorly mineralized bones in children • Osteoporosis: group of diseases in which bone resorption outpaces bone deposit o Risk factors: age, petite body form, insufficient exercise to stress bones, diet lacking in calcium, smoking o Treatment: calcium and vitamin D supplements, hormone replacement therapy o Preventing it: consume enough calcium, limit carbonated beverages, get plenty of weight bearing exercise • Paget’s disease: excessive and haphazard bone deposit and resorption o Causes spotty weakening of the bones Notes from Powerpoint Lectures Endochondral ossification • Hyaline cartilage is a template o It will be replaced with bone o It is not converted it is replaced o Starts in prenatal development o Remnants of the template can be seen: articular cartilage covering the epiphyses and the epiphyseal plate 1. Bony collar forms around diaphysis by osteoblasts that lay down osteoid and mineralize it. This is going to stress the cartilage which will kill it. It provides the underlying support for the diaphysis to grow and exist while the cartilage decays. (about 9 weeks after conception) 2. Chondrocytes hypertrophy (get larger), mineralize the cartilage which will cut off all nutrient access so they die. Deterioration of cartilage that makes up the diaphysis. 3. Infiltration of blood vessels, nerve endings, lymphatic vessels. This brings a fresh supply of cells. Bone starts to grow. 4. Medullary cavity forms. Compact bone that makes up diaphysis fuses with the bony collar. Epiphyses just now start to form secondary ossification centers to deteriorate the cartilage and start to grow bone. (about the time of birth) 5. Ossification of epiphyses, bone finishes development. (after birth) Bone growth in long bones • Occurs at epiphyseal plate o note: epiphyseal plate= bone still growing…vs epiphyseal line=bone done growing o Region that separates the diaphysis from epiphysis o Includes hyaline cartilage • Extending length of diaphysis o Pushing epiphyses farther apart • Growth plate can be broken down into different regions o Ossification zone: region facing diaphysis, area of bone formation replacing cartilage o Calcification zone: above (closer to epiphysis) ossification zone o Hypertrophic zone: above calcification zone o Growth/Proliferation zone: region next to epiphysis, cartilage cells present at border of epiphysis and growth plate have access to nutrients and multiply and divide to produce new cartilage o As you move away from epiphyseal plate, cartilage cells start to hypertrophy because of stress (lack of nutrients because further away from nutrients). § Hypertrophied cartilage cells secrete calcium which calcifies the cartilage which kills the cartilage cells § This is a trigger for ossification zone to replace the decaying cartilage with bone § New cartilage is formed at the border of plate and epiphysis § New bone formed at border of diaphysis and plate • Even when bones are done growing longitudinally, they can still grow thicker or thinner • Growth ends when epiphysis and diaphysis fuse What determines growth rate? • Growth hormone o Stimulates production of bone and cartilage growth at the plate § Person gets taller o Doesn’t work well unless thyroid hormone is present o Excess hormone will cause you to be tall o Deficiency= will be short • Thyroid hormone o Permissive hormone: Won’t let other hormones do their job without it present o Excess does not affect if you get taller o Deficiency= will be short • Sex hormones o Hit puberty more sex hormones release o Causes rapid growth o Girls stop growing sooner Bone remodeling • Continues throughout life • Balance between the amount of Bone resorbed (broken down) and deposited (formed) • Bone is dynamic: 5-7% of bone mass recycled per week • Deposition o New bone formation o Osteoblasts o Occurs after injury or for additional strength o Several things promote bone deposition § Vitamin C: collagen synthesis § Vitamin D: calcium absorption § Vitamin A: balance deposit and resorption § Minerals: calcium, phosphorous, magnesium • Resorption o Breakdown of bone matrix o Osteoclasts o Functions: Raises blood calcium levels, removes necrotic debris o To accomplish this they use § Lysosomal enzymes: digest organic matrix § Acids: convert calcium salts to soluble form • Hormonal regulation of bone remodeling o Hormones involved § Calcitonin • Secreted by thyroid gland • Less important than PTH § PTH • Secreted by parathyroid gland • More important than calcitonin § They are antagonistic hormones o Negative feedback system: high blood calcium level § Drink glass of milk § Blood calcium levels rise above normal range • Cells in thyroid gland detect this § Calcitonin is secreted • Inhibits secretion and action of PTH • By inhibiting PTH, osteoblast activity increases relative to osteoclast activity, this encourages deposition § Calcitonin stimulates calcium salt deposit in bone § Homeostasis restored o Negative feedback system: low blood calcium level § Don’t drink enough milk § Blood calcium level falls • Parathyroid glands detect low blood calcium level § PTH is secreted § PTH stimulates osteoclasts to release lysozymes that break down collagen and secrete acid that mineralizes the mineral, which gets released into the blood stream § Raises blood calcium level § Homeostasis restored • Mechanical stress: regulation of bone remodeling o Wolff’s Law: bones grow or remodel in response to the demands placed on them § Stress a bone: it will get thicker, stronger, denser § Don’t stress a bone: it will get weaker o Long bones: thickest at midpoint of diaphysis o Curved bone: thickest where most likely to buckle o Trabeculae: form struts along lines of compression o Large bony projections: occur where muscles attach Bone disorders • Osteomalacia (soft bones) o Inadequate mineralization § Produce osteoid, lay down collagen, but insufficient amount of calcium to mineralize it o Bones are more flexible o Pain when weighted o Treatment: vitamin D supplements o Rickets in children o Bow legs o Deformities to pelvis, skull, and rib cage • Osteoporosis: bone resorption greater than bone deposition o Weakened, brittle bones o More common in women than men § Especially post-menopause § Treatment could be Hormone replacement therapy (HRT) o Usually sets in later in life o Prevent it: exercise, good nutrition • Paget’s disease: excessive bone formation and breakdown o Abnormal ratio of spongy bone to compact bone § Lots of spongy bone compared o May see spongy bone at the surface o Poor mineralization of new bone o May be viral in origin Bone repair after a fracture 1. Hematoma forms a. When: shortly after break b. Clot forms c. Injured cells die d. Swelling and pain e. Platelets try and plug up blood vessels f. Stop the internal bleeding 2. Fibrocartilaginous callus formation a. When: within 2-4 days after b. Infiltration of fibroblasts, chondroblasts, osteoblasts, osteoclasts i. Clean up debris ii. Start laying down collagen iii. Lay down cartilage 1. Which will be replaced with bone iv. Lay down bone c. Soft callus (granulation tissue) d. Capillaries form 3. Boney callus formation st a. When: by end of 1 week b. Too weak to be weight bearing c. Spongy bone forms d. Connects ends of bones 4. Bone remodeling a. Begins with boney callus formation b. Remodeling takes some time c. Area that was fractured will be thicker and stronger