hbio301 ch6 bones and skeletal tissue

osteocytes are _, act as _, communicate w_

"- mature, long lived, terminally differentiated, multifunctional cells w long cytoplasmic processes ('dendrites') found in lucuno-canalicular network - act as mechanoreceptoinrs via canaliciular tethering elements such as integrin and glycocalyx coat to the ECM and/or fluid shear that transmits forces to open hemichannels in processes ('dendrits') - w osteoblasts and clasts to regulate bone remodeling + large # of toher cellular processes such as glucose homeostasis, cognition, male fertility"

endochondral ossification

"- ossifiies bones that originate as hyaline cartilage(caleld ""cartilage replacement bones"") - all bones other than those in intramembranous - begin forming late in 2nd month of embryonic development and continues forming until early adulthood - 5 steps"

4 steps of fracture repair

"1. hematoma formation - blood clot forms fibrous network and bone cells nearly die 2. fibrocartilaginous callus formation- within few days new blood vessels form and rapidly dividing fibroblasts and chondroblasts in nearby periosteum & endostem invade clot to form soft callus; continiue to secrete additional fibers to form fiborcartilage&hyaline- fibrocartilaginous callus 3. bone callus formation- within a week osteoblasts replace central cartilage w spongy ""woven"" bone via endochondrial ossification. trabeuclae span callus to reunite bone 4. bone remodeling- osteoblasts and clasts continue to remodel bone for ccouple months, laying down both spongy & compact bone (so briefly stronger bc end is trabeculae)"

osteoblasts are bone cells that actively secrete _, mechanisms:

- bone matrix- osteoid (collagen + glucopolysaccharides), osteocalcin (signalling), osteopontin (extracellular glycoprotein but also involved in inflammation, mechanical stress, angoigenesis, and accelerated bone resoprtion) and alkaline phosphatase (ALP) involved in mineralization - groups of interconnected osteoblasts cause calcum salts and phosphorus to precipitate from blood and bond w newly formed osteoidi andn ALP catalyzes calcium phosphatee preciptiation (found in extracellular matrix vesicles)

basic structuree of cartilages

- cells = chondroblasts, chondrocytes (located within in lacunae) - matrix contains: fibers, gel-like ground substance

as adolescence comes to end what happens

- chondroblasts divid less often - epiphyseal plates become thinner (cartilage sopts growing and is replaced by bone tissue) - bones stop lengthening when diaphysis and epiphyses fuse (17-25 yo)

perforating fibers connect w _, functions:

- collagen fibers in bone and joint capsules - isolation of bone from surrounding tissue, entryway for cardiovascular & nerves, participates in growth and repair of bone

anatomy of bone

- compact bone (80% of skeleton)- denser outer layer of bone - spongy, cancellous/trabecular bone (20%)- internal network of bone - trabeculae in spongy bone- little beams of bone lighten load - open spaces between trabeculae filled w marrow and hemopoietic cells

structure of short, irregular, and flat bones

- contain bone marrow but no marrow cavity - diploep internal spongy bone of flat bonesn

intramembranous ossification (dermal ossification)

- develops directly from mesenchymal membrane - produces membrane or dermal bones (includes most of the bones of the skull, face, lower jaw, lateral portion of clavicle - 4 steps

bones most effected by aging _ resulting in _

- epiphyses, veretbrae, jaws - fragile limbs, reduction in height, tooth loss

women vs men lose bone mass do to what (women lose more % per decade)

- esp after menopause when there is precipitous decline in estrogen - primiarly to loss of estrogen (as testosterone levels decline, less estreogen is made from aromatase

estrogen/hormones and bone loss

- estrogen affects osteoprotegerin (OPH)/receptor activity of NF-kB ligand (RANKL) system important in balancing activity of osteoclasts - estrogen and androgen help maintain bone mass by inhibiting osteoclast activity

osteoclasts (clatos greek for broken)

- giant multinucleated cells derived from hemocytoblast cell line of WBC that also produces macrophages - responsible for resoprtion of bone - secrete hyrogen ions, collagenase, cathepsin K , hydrolytic enzymes, gelatinases (the hydrochloric acid dissolves the mineral salts and the enzymes digest the organic materials)

spongy bone

- less complex than compact bone, lacks osteons - trabeculae contain layers of lamellae and osteocytes but lack blood vessels (endosteum has capillaries) (compact doesnt have trabeculae, and has less osteocytes bc not as much space) - red (or in some bones yellow fat) bone marrow fills space between trabeculae - red bone marrow has blood vessels that supply osteocytes and has blood cell progenitors

osteons structure, function, components

- long cylindrical - support - have lamellae, central canal, perforating canals, canaliculi

long bones, found in

- longer than wide, a shaft plus ends - arms legs hands feet fingers toes

osteogenic (osteoprogenitor) cells

- mesenchymal stem cells that differentiate into ostoeblasts and chondroblasts - located in both endosteeum & periosteum to assist in repair

hyaline (latin glassy) cartilage vs. elastic vs. fiibrocartilage

- most abundant - chondrocytes appear spherical - collagen unit fibril is only type of fiber in matrtix - ground substance holds a large amount of water - provides support throguh flexibility vs. - many elastic fibers - able to tolerate repeated bending - locations -epiglottis, pinnae, auditory tube vs. - resisstt strong compression and strong tension - intermediate between hyaline and elastic cartilage

bones are considered to bbe organs bc they contain several types of tissues

- mostly supportive bone CT, contain nervous & other CT, contain articulating and other cartilages in joints, epithelial tissue line blood vessel

3 broad categories of bone markings (ways to deal w stress)

- projections for muscle attachment, surfaces that form joints, depressions and openings

short bones, found in

- roughly cube-shaped, small thiick - ankles wrists

sutural bones, found in

- small irregular bones - found between flat bonese of skull

sesamoid bones, found in

- small, flat - develop inside tendons near joints of knees, hands, feet

perichondrium

- surrrounds elastic and some hyaline cartilages (not fibrocartilage or hyaline articular cartilages) - resists outward pressure - functions in growth ahd repair of cartilage (as contains chondroblasts) - consists primarily of water - is a resilient tissue, springs back to original shape

flat bones, found in

- thin flattened, parallel surfaces, usually curved - skull sternum ribs scapula

location of cartilages

- throughout adult body: elastic cartilage in external ear, epiglottis, auditory tube; hylaine cartilage in joints, nose, costal cartialge, & resp system (larynx, trachea, bronchioles); fibrocartilage in intervertebral discs, knee menisci & pubic symphysis

irregular bones, found in

- various shapes - spinal vertebrae, pelvic bones

tx for osteoporosis beyond vitD (4)

1. antiresoptive drugs - bisphosphonates (PPi-inorganic pyrophosphates resistant to hydroxyapatite degradation), SERMs (selective estrogen receptor molecules) 2. anabolic agents- calcitonin 3. estrogen replacement therapy (ERT) or hormone replacement thereapt (HRT- estrogen + progestin/progesterone) - generally not first choice bc potential negative side effeccts include icnreased risk breast cancer?, blood clots, endometrial cancer) 4. drugs that block steoclast formation/function - denosumab

steps of endochondreal ossification

1. bone collar forms around diaphysis of hyaline cartilage model 2. cartilage in center of diaphysis calcifies then develops cavities 3. periosteal bud invades internal cavities, spongy bone begins to form 4. diaphysis elongates & medullary cavity forms as ossification contiues, secondary ossificiatioin centers appear in epiphyses (vascularized via epiphyseal blood vessel) 5. epiphyses ossify. when completed, hyaline cartilage remains only in epiiphyseal plates and articular cartilages

epiphyseal growth zones from resting zone

1. chondroblasts at top (proliferationi zone) divide quickly (Mitosis) 2. lengths entire long bone via osteogenesis (in hypertrophic zone older cartilage cells enlarge) 3. calciification zone: older chondrocytes signal surrounding matrix to calcify then cells die then matrix deteriorates (leaves long trabeculae/spicules of calcified cartilage on diaphysis side, trabeculae partly eroded by osteoclasts) 3. ossifiicatioin zone: new bone is forming (osteoblasts cover trabeculae w bone tissue, trabecculae eaten away from tips by osteoclasts)

steps of intramembranous ossification

1. ossification centers appear in fibrous CT membrane - center formed by selected centrally located mesenchymal cells cluster and differentiate into osteoblasts 2. bone matrix (osteoid) secreted within fibrous membrane and calcifies - osteoblasts secrete osteoid(collagen+glucopolysaccharides) that is calcified in a few days (calcium salts&phosphorus precipitate from blood to interstitial fluid), trapped osteobalsts become osteocytes (secretes alkaline phosphate required for extracting inorganic phosphate from precipiitated phosphorus to form hydroxyapatite which forms bone) 3. woven bone and periostetum form - accumulating osteiod laidi down between embryonic blood vessels in random way ->network of trabeculae- woven bone (rather than lamella); vscularized mesenchyme condenses on external face of woven bone and becomes periosteum 4. lamellar bone repaces woven bone, just deep to periosteum. red marrow appears - trabeculae deep to periosteum thicken and later replaced w mature lamellar bone forming compact bone plates, spongy bone (diploe) consisting of distinct tarbeculae persists internally and vascular tissue becomes red marrow (ie diploe cavities contain red marrow)

bone is made up of

1/3 extracellular matrix protein fibers (primarily type 1 collage), 2/3 crystalized hydroxyapatite

skeleton grows until age of

17-25yrs

we cycle mineral reserves, recycle and reuse bone matrix: in adults, cancellous (spongy bone containing red bone marrow is replaced every _ yrs, while compact bone is replaced every _yrs

3/4, 10

most common load experienced by bone

bending

growing bones widen as they length via osteoblasts and osteoclasts by adding/removing bone tissue where

blasts add bone tissue to external surface of diaphysis, clasts remove bone from internal surface of diaphysis

compression fracture

bone crushed, common in porous bones (osteoporotic) subjected to extreme trauma like fall

comminuted fracture

bone fragments 3 or more pieces, common in aged whose bones are more brittle

simple fractures vs compound

bone only (no skin involvement) vs bone protrudes through skini

ossification (osteogenesis)

bone tissue formation

skeletal system is comprised of

bones of skeleton, cartilages, ligaments, other CT

where is osteocalcin involved in terms of bone to a part of the body

brain, muscle, testes

depressed fracture

broken bone portion pressed inward, typical skull fracture (Cyborg MMA)

bone generates what type of matrix

calcified

calcitriol/ vitamin D3 (kidney&skin) promotes _ and _ absorption in digestive tract

calcium, phosphate

appositional growth is also known as , where are chondroblasts

children, limited repair in adutls; in pereichondrium produce new cartilage

types of reductions (tx for fraccture by reallignment of broken ends)

closed- bones coaxed into position by physician open- bones joined surgically w pnis and wres

during bending load, bone experiences both

compression &tension

osteoclacin & rest of body

crosses blood-brain barrieir and acts in brainstem, midbrain, hippocampus to influence synthesis of several neurotransmitters that favor learning and memory formation

in bone remodelling, osteoblast _ and osteoclasts _ bone

deposite, reabsorb (osteoclasts are HCL and lysosomal enzyme secreting giant multinucleated ceells that are derived from hemopoietic cell line/self-fusing macrophages)

structure of typical long bone

diaphysis (shaft of bone), epiphyses (ends of bone) , metaphysis (between epi and dia), blood vessels (well vascularized), medullary cavity (hollow cavity filled w yellow and/or red marrow), membranes (outer periosteum, perforating collagen fiber bundles (sharpeys fibers), inner endosteum)

displaced fracture

displaced from normal

"colles' fractures"

distal portion of radius bone typically caused from when breaking your fall w your hand (profs) (transvrese)

interstitial growth is also known as ,

embryonic growth at epiphyseal plate (3D), chondroblasts within cartilage divide and secrete new matrix

mesoderm gives rise to

embryonic mesenchyme cells

durinig childhood and adolesccense bones length entirely by growth of the

epiphyseal plate (maintains constant thickness so whole bone lengthen, cartilage replaced w bone CT as quickly as it grows)

growth hormone (pituitary) stimulates

epiphyseal plates (used for dwarfism)

epiphyseael fracture

epiphysis separates from diaphysis along epiphyseal plate, tends to occur where cartilage cells are dying and calcification of matrix is occuring

in children and adolescents, bone formation _ rate of bone reabsorption in young adults.... in old age...

exceeds, balance, reabsoprtion predominates & mass declines

Fracturese shold take 6-8 weeks or longer to repair depending on

for weight-bearing bones (quicker ie 6-8) or longer (age)

compression &tension

greatest at external surfaces and zero in middle, whcih in long bones is hollow (medullary cavity)

_ synchronzies interstitial cartilage growth growth with osteogenesis as well as appositional bone wideniing so that load bearing is balanced w growth

growth plate

bone is a complex composite material consistinig of

high elastic modulus of stiff hydroxyapatite crystal for compressive strength, embedded in low elastic modulus of flexible organic collagen fibers provide tensile strength, permeated pores filled w osteocytes in lacuna

greenstick fracture

incomplete break (only one side of shaft breaks, other bends), common in children whose bones have more organicc matrix/are more flexible than adults

torus fracture

incomplete buckle fracture, often distal portion of radius, most common fracture in children (greenstick)

endosteum

incomplete cellular layer that - lines medullary (marrow) cavity - covers ttrtabeculae of spongy bone - lines central canals - contains osteoblasts,-genitor or -genic, -clasts - active in bone remodeling and repair

Leydig cells have osteocalcin receptors which _ testosterone

increases

fibroblast growth factor 23 (FGF23) & rest of body

increases phosphate reabsorption in kidneys and absorption in gut (bone to kidney)

appositional growth is growth of bone by addition of bone tissue to where

its surface (thickening)

periosteum covers all bones eceept parts enclosed in

joint capsules

compact bone have

lamellae (incomplete or circumferential, multiple in single osteon), osteons

exercise increases _, which promottes osteocyte health, facilitates glucose uptake by skeletal muscle, improves hepatic glucose and lipid metabolism

leptin

classification of bones

long, short, flat, irregular sutural, sesamoid

fragility fractures

low energy fractures of thoracolumblar vertebrae, pelvis, distal radius, proximal and distal femur, tibia and proximal humerus

osteopenia is a BMD (bone mineral density _ than normal when compared to a 30 yr old white women, measured by DEXA scan; osteoporosis score?

lower (t-score between -1 and -2.5), t-score less than -2.5 SD

bone tissue osteocalcin signalling

mechanical loading (stress) sensed by osteocytes is conveyed to osteoblasts that secrete osteocalcin which results in increased neurons firing ^ testosterone production, decreased adiponectin secretion; increased: insulin sensitivity, adiponectin production; mitochondrial boigenesis, glucose uptake, fatty acid uptake, muscle mass; GLP-1 secretion, insulin production, B-cell proliferatoin; decreased: fat accumulation

mesenchyme produces

membranes, cartilage

gut microbiome to bone via liver/fat cells

microbes release short-chain fatty acids that cause liver/fat cells to make more insulin-like growth factor: 1IGF-1, which promotes bone growth

during exercise muscles make _, muscle & bone growth inhibitor. in addition, _ influences fat and insulin responses to the increased energy use and protects osteocytes from ROS

myostatin, beta-amnioisobutyric acid (BAIBA)

tx for osteopenia

no specific meds, but can prevent further bone loss

bone tissue componenst

organic (cells, fibers, ground substance), inorganic (mineral microcrystals that precipitate bony matrix

estrogen and testosterone stimulate _

osteoblast (estrogen later induses closure of epiphyseal plates)

ccacncerous tissues release _ that can produce severe osteoporosis

osteocclast-activating factor

parathyroid hormone indirectly stimulates

osteoclasts (via osteoblasts) to increased activity, increases blood calcium

calcitonin (c cells of thyroid) inhibit

osteoclasts, promotes calsium loss by kidneys (rather than bones)

cells of bone (4)

osteocytes (90-95%), osteoblasts, osteogenic or osteoprogenitor cells, osteoclasts

PGE2 & rest of body

osteocytes make prostaglandin E2 (PGE2) which promotes muscle growth

disorders of bone and description

osteomalacia- occurs in adults, bones inadequately mineralized; rickets- occurs in children analogous to osteomalacia(softening), due to inadequate vitamin D in diet or inadquate sun exposure (1930 US mandate all milk needs to be fortified vitamin D); osteosarcoma- form of bone cancer affecting 10-25 yr olds

2 disorders of severe bone loss

osteopenia, osteoporosis (severe)

periosteum includes

outer fibrous layer of dense irregular CT, inner cellular (cambium) layer that contains osteoblastes, -cytes, -clasts, -progenitors; perforating fibers (collage fibers of periosteum)

bone remodeling occurs at _ and _ surfaces

periosteal, endosteal

thyroid hormone ensures the skeleton retains

proper proportiions

spiral fracture

ragged break occurs when excessive twisting forces are applied to a bone, common sports fracture

transverse fracture

right angle to long plane

anatomy of a bone reflects

stress

bone markings on _ surface of bones reflect stress on them

superficial

functions of skeletal system

support(provide hard framework), movement (skeletal muscles use bones as levels), protection (of underlying organs), mineral reserve/storage (reservoir for important minerals), blood cell formation (bone contains red marrow), endocrine function (osteoblasts secrete osteocalcin, which is involved not only in bone and calcium homeostasis but also glucose homeostasis and exercise capacity, brain development, cognition, and male fertility)

leptin & rest of body

supresses appetite and bone growht which may save energy for day to day functions when food is scarce (fat cells to brain)

in epiphyseal plates of growing bones cartilage is organized for quick efficient growth, cells form:

tall stacks - pushes epiphysis away from diaphysis - occuurs from birth till early 20s, after puberty, epiphyseal lines can be seen on x-rays

"pott's fracture"

variety of bimalleolar ankle fractures, involving both lateral (fiibula) and medial malleolus (tibia), caused by combined abduction external rotation from eversion force (kinda displaced)

gut microbiome to bone via large intestine/liver/kidney

vitamin K (of which half our daily intake is from gut microbiome) is required for proper hydroxyapatite crystal formation

cartilage grows quickly in _, skeleton shows fewer chondrocytes in _ bc _

youth, elderly, membranes and cartilage ossify