Bone Flashcards
Bone tissue (4)
Mineralised ecm - rigidity and hardness, resistant and light
Continuous remodelling
Bones, dentin, cementum
Supportive connective tissue?
Bone and cartilage
Functions of bone tissue (5)
Skeletal - framework Mechanical - intertion of tendons and ligaments Protection of organs Trophic - calcium storage Hematopoietic - rbc formation
Component of bone and 2 types
65% calcium hydroxy apatite
23% col
10% water
2% non col proteins
Organic - resistance to tensile pression forces
Inorganic - rigid, hard
Bone destroyed - inorganic and organic component
Inorganic - loss of rigid and hardness - bone retain resistance but flexible
Organic - bone shape and size maintained - fragile like porcelain
Bone tissue classification? 2
Non lamellar - woven bone - intertwined (inferior vertebrates, fetal bones, fracture repair). Parallel fibres (birds)
Lamellar mature (compact) - outer shell flat bones, surface short bones, dia+epi(physis) of long bones (Spongy) epiphysis of long bone, short bones
Primary bone (5)
In embryogenesis eg fetal bones
Irregular intertwined fibres
Progressive remodelling. Replaced with lamellar bone
Initially formed - bone fracture repair
Less mineralised - diff mechanical properties
Quick bone structure?
Osteon, interstial lamellae, inner-outer circumferential layer, harversian canal, osteocytes in lacunae, canaliculi sharpey fibres, periosteum bv
Purpose of canaliculi?
Osteocyte Communication at diff levels
Periosteum and endosteum contains?
Deep layer - Osteoblasts formed from osteoprogenitor cells -> generate new bone tissue
BV AND DCT
Outer, intermediate, deep layer
Sharpey fibres - perforating - collagen bundles enter into bone matric
Osteon (4)
3 types of canals in bone?
Concentric lamellae
0.9-1.2mm
5-20 lamellae
Canaliculi - communication between osteocytes
Canals - haversian, volkmann, canaliculi
System of lamellae?
Parallel fibres of collagen - increase strength - absorb diff mech stress
During bone remodelling?
Pre-existing osteons destroyed(interstitial lamellae), new ones formed.
Methods to study bone tissue (2)
Decalcified bone - inorganic component removed via acid. - stained with hande for soft tissue
Ground bone - remove cell and bv. Preserve organic, mineral component. Moethod : cut using saw. Ground to suitable thickness.lacunae + canaliculi = black
Lamellar spongy bone ( medullary cavities + trabeculated bone)
Where bone marrow located?
Epiphysis bone marrow only.
Cross section - lamellae, not true osteon, thinner. Same morphology of osteocyte.
Trabeculae - thin, irregular lamellae - osteocytes. Endosteum, no haversian canals, interconnected canaliculi, 3D structure,
Difference between periosteum and endosteum?
Endo - inner surface of bone cavities
Single layer osteoprogenitor cells
Thinner than periosteum. Provide nutrition to cells
Cells types on bone(5)
Osteoprogenitor
Bone lining on bone surface
Osteocytes - mature cells, not secrete matrix
Osteoblast - not divide - secrete matrix + collagen fibres - cuboidal cells
Monocytes -> Osteoclast - bone reabsorped. Ruffled border
Osteoprogenitor cells?
Similar to fibroblast. 1 layer surface on perio/endo steum
Osteoblast
Cuboidal. Well developed golgi rer
Produce ecm, recptor for pht- stimulated - osteoblast stim osteoclast
In matrix = osteocytes
Bone lining cells
Surface of bones where no remodelling,derived from osteoblasts,
Support osteocytes
Regulate calcium in matrix
What directly stim osteoclasts?
Calcitonin
Osteocytes
In lacunae, canaliculi, non mineralised - allow movment of nutrients
Flat cel body
Mature, abundant, quintescent
Function - mechanotransduction - rel factors - mod preosteoblast activity
Osteocytes canaliculi
Gap junction. Nutrients via bv in central canal
Mechanotransduction- actin network - movement of nutirents
Osteoclasts
200-109um, multinucleated (syncitium), polarised cells
Monocyte linage
Podosome - adhesion - increase sa
Calcitonin receptor
Large no of golgi, rer, mito
Howship lacunae under cell
Lysosomes - h2co3 provide protons - acidic pump - activate lysosmal enzymes . Only under cell - therefore not dmg other portion of bone
Activated by factors released by osteoblasts (pth indirectly)
Bone dev. Intramembraneous, direct
Form same histological structure as
Mesenchyme - large no of vessels
Differentiate into osteoblast - secrete matric - osteoid
Osteoid not mineralised - become mineralised -> bone increase in size
Bone formation and mesenchyme?
Mesenchyme Cell proliferation - form condensed mesenchyme.
Direct and indrect ossification forms?
Direct - flat bones of skull, face and clavicle, embryo in the mesenchyme
Indirect - cartilage - temp replaced by bonr
Base of skull
Vetebrate
Bones of extremities + axial skeleton
Direct ossification mechanism?
Alkaline phosphatase - hydrolyse po4-
Increase and high lvl of po4-
Nanocrystal form in and around matrix vesicles
Calcium hydroxyapatite surround collagen fibres
Mineralisation of bone tissue in direct oss.
Hardness of bone
Osteoblasts deposit osteoid
Deposition of calcium hydroxyapetite between collagen fibres
Indirect oss
Endochrondral. Most long and short bones
Precursor model of cartilage - almost completely replaced with bone tissue
Mineralisation of cartilage - removed - deposition of bone. Cartilage remain at articular surface
Endochrondral oss. Mesenchyme ->….
Condensed mesenchyme, hylaine cart, hypertrophic cart, calcified cart, chondrolysis, endochrondral oss (bv invade, invading mesenchyme diff into osteoblast -> deposit osteoid)
Which cell perform chrondrolysis?
Chrondrocyte
2 modalities of indirect oss.
Perichondral - surface of cart
Endochrondral - inside cart
Endochondral steps (5)
Bone cart form - cart model - interstial(length), appositional(width) growth. Chondrocytes central - enlarge, die - calcified matrix.
Bone collar form
Prim oss centre
Chondrocytes hypertrophy -> lacuna
Secondary oss centre form
Perichondral steps
Basic cart form
Periosteum - osteoblasts cover surface in thin layer of bone
Bv invade cart - new osteoblast form prim oss centre
Medullary cavity - + more, diaphysis: bone replace cart
Post birth - 2 oss centre. Secondary oss centre form. Epiphyseal plate - located in metaphysis
Outline of bone growth from embryo to matrix adult
Embryo 5-6 w - hyaline cart
“” 6-8 w - periosteum form
Fetal 8-12 w - prim oss centre form
Post natal - cancellous bone, calcified cart
Prepubertal - cancellous bone at ends
Matrix adult - articular cartilage at ends
Length and grwoth of bone?
Growth until length achieved - epiphyseal cart completely replaced (metaphysis)
Bone xray - incomplete oss (2)
Epiphyseal line - black line - lack of mineralisation
Also determine age
Primary bone production
Occur during embryo dev + bone healing
Large no of osteocytes, interwoven collagen, less mineralisation
Seoncary bone formation
Mature bone -> osteons (lamellar compact bone)
Repair of fractured : 4 steps
Hematoma form - blood clot
Callus form - soft callus (fibrocartiliginous)
Bony callus form - hard callus
Bone remodelling - spongy part of bony callus -> compact bone
Bone remodelling? Increase diameter, thickness,
Appositional growth
Bone vessel on surface of bone - encircled by bones -> form lamellae - ultimately form harversian canal
Oldest lamellae on outside. Newest = inside
Remodelling unit (2). 2 zones. 2 phases
Osteoclast/blast remodelling process
2 zones - closing : osteoblasts on inside - form new osteon
- cutting cone : osteoclasts on inside
Resorption phase : 2/4 weeks
Formation phase : 4-6months
Bone tissue regukated by? Hormones, nutrients, exercise
Hormones - pth, caltitonin, gh
Nutrients - calcium, vit d -> increase absorption of ca2+ by SI
EXERCISE - mechanical stim - remodelling of bones - modify position of new matrix
What hormones: stim osteoblasts, stim/inhib osteoclasts, increase absoprtion of ca by si
Stim osteoblasts - gh, thyroxine, sex hormones
Stim osteoclasts - pht
Inhib osteoclasts - calcitonin
Calcitriol - increase absorption of ca by SI
Osteoporosis
Increase osteoclasts - increased reabsorption - new bone - weaker - increased risk of fracture
Skeletal muscle - no. Of nuclei?
Organisation of filaments in muscle fibres
Where skeletal muscle found?
Multiple. Located beneath sarcolemma. Syncytium.
Skeletal+cardiac = striate
Skeletal - insert onto tendons - linked to bone - found in tongue, pharynx, esophagus, mimic muscles
How morphological unit of skeletal muscle derived?
From fusion of myoblasts (mononuclear,l undiff, no myofibrils) - myofibrils (filaments in parallel array) + other organelles.
Striated perpendicular to longi cut
Muscle regen - satellite cells
Satellite cells surround muscle fibre - involved in muscle regen - fuse - myotubules form - replace lesions
Cardiac muscle -> lose myocytes?
No satellite cells -> no regen
Endo, peri, epi mysium
Endo - reticular fibres surround muscle fibres. Small bv and nerve parallel to fibres
Peri - larger bv and nerves. Thicker ct. Fascicles -> function of muscle fibres as a whole.
Epi - Sheath dct. Penetrated by Major bv and nerve supply.
In cross section and longi of skeletal muscle?
Cannot detect striations
Polygonal cells
Peripheral nuclei
Longi : z lines, a i band, h zone, nucleus at periphery
Skeletal. Dark band?
H band?
Area of overlap?
M line contains?
A band is dark and area of overlap.
H band only thick filaments
M line - proteins - maintain thick fil in correct position.
Size of thick and thin filament?
Thick :10-12nm
Thin : 5-7nm
Sarcomere proteins (3)
Titin - maintain thick filaments - correct arrangement in sarcomere
Nebulin - non elastic - maintain correct length of thin filaments
Actinin - bind actin to z line
G actin + f actin?
Myosin head?
Polymerisation of g actin form f actin req atp
Myosin head - 2 peptides - active site attached to actin filament
Troponin (3) steric blocking mechanism
3 subunits TIC
TNT - bind to tropomyosin
TNI - bind to actin filament
TNC - bind to calcium
Other muscle fibre proteins? (5)
Desmin - int fil - insert into costamere - link z lines
Plectin - connect adjacent desmin
Ab crystallin - heat shock protein - protect desmin from stress induced dmg
Alpha-actinin - anchor actin to z-disk
Dystrophin - links sarcolemma to actin. Mutation - muscular dystrophy. Vital in cell stability
Tropomodulin - actin capping protein - prevent polymerisation
Structure and protein of m line
Maintain correct arrangement of myosin filaments
Proteins - myomesin, m protein, schlemin
Electron dense
Sliding filament theory?
Overlapping of thick and thin filaments
Mechanism of sliding filament theory?
Atp + myosin head- atp hydolysis - myosin head 90, myosin bind to actin release adp + pi, myosin head -> 45
Calcium released into….
Atp bind to myosin head causes?
Via T tubules into sarcolemma
Atp bind to myosin head -> detachment from actin filamments
Rigor mortis? (3)
Stiffening of muscle after death - 24/48 hr muscle proteins broken down - allows muscle to relax.
No oxygen - no atp - atp not bind to myosin head - unable to relax
Skeletal muscle triad
At boundary between A and I band.
2 terminal cisternae of sr
1 tubule
H band = central portion of traid
NMJ, structure, toxins, disease
Large no of infoldings. Ach,
Toxins - botulinum(block rel of ach), curare(block ach receptors), neostigmine(block removal of ach), neurotoxins(block ach receptors)
Myasthenia gravis - auto immune disease. Attack ach receptors. Lost…
3 types of skeletal muscle fibres?
Type 1 - slow oxidative - red slow twitch
Type 2a - fast oxidative glycolytic fibres - intermediate
Type 2b - fast glycolytic fibres - white/pink - fatigue. Fast myosin atpase velocity. Lactic acid
Which stain to differentiate skeeltal muscle fibres
Succinate dehydrogenase
Type 1 skeletal muscle fibres
Slow sustained contractions.
Large mito
Myoglobin
Large no of cappillaries
Postural muscles of axial skeleton.
Resisatnce to fatigue - oxygen remains - no lactic acid produced.
Low glycogen level. Glucose completely used up.
Type 2 intermediate fibres
Many mito.
Anaerobic and aerobic respiration.
Fatigue.
Generate high peak tension. Lower limbs. Contract similar to fast twitch
White slow twitch muscle fibres?
Easily fatigue.
Low mito and capp
Low myoglobin
High no, of glycogen. Anaerobic respiration. Creatine phosphate pathway.
Fast powerful contractions.
Digit movements, extraocular muscles. Fine precise movements.
Greater no, of NMJ than slow twitch.
Hypertrophy and atrophy (3 each)
Hyper - increase in muscle size, no. Of myofilaments. Stim by resistance training, testosterone, anabolic steroids
Atrophy - reduction of muscle fibre size, cells smaller + size, due to pathology - removal of nerve, immobility, lack of use
Cardiac muscle tissue. Where? And joined by? Innervation? All layers of muscle(5)
Myocardium - heart contraction (cardiomyocytes) - joined by junctions (intercalated disks-dark lines)
Innervation - autonomic nervous system
Layers - pericardium - serosa cavity - epicarium - myocardium - endocardium
Cross section of cardiac and how different from SM?
Some nucleus(maybe multiple) seen, striated, granules -> presense of myofibrils
SM NO graules, homogenous cytoplasm
Cardiomyocytes(2)
Elingated (100um) Rounded nucleus (sometimes 2)
What surrouds cardiomyocytes?
Ct -> bv therefore vascularised - cardiac bundle = avasular
Intercalated disks
EM -> desmosomes (strong adhesion)
Longitudinal -> gap junction, calcium movement
Transverse - adherens junctions - cadherin + b catenins
Connect cardiomyocytes - mechanically, chemically, electrically - mass of cells contract together
Cardiomyocytes extras (2)
Mito seperate myofibrils
Adhering junctions bind actin at z-lines
Cardiac muscle - diads
Only one t tubule - larger than in skeletal muscle. At z lines.
Nuclei of cardiac and skeletal muscle?
Cardiac - at center
Skeletal - periphery
Cardiac muscle and heart conduction?
Purkinje fibres - modified muscle cells - (less myofibrils, less contraction, more conduction of impulse) - not specialsed for contraction.
SAN -> AVN - ventricles
Sm - thick and thin filaments?
Thin - actin, tropomyosin, caldemon, calponin (last 2 are ABP) block myosin binding site
Thick - 2 heavy and 4 light chains - myosin 2. Side polar thick filament. No central bare zone. Tapered bare ends.
Sm contractile proteins essential to regulation?
Alpha actinin - structural support to dense bodies
Calmodulin - bind to ca - activates mlck
Myosin light chain kinase - phosphorylates myosin light chain - therefore able to bind to actin filament
Which enzyme in sm, inactivates myosin?
Phosphatase - dephosphorylates
Dense bodies?
Anchor intermediate filaments, a-actinin and actin and myosin filaments to sarcolemma.
Anaologs of z line in skeletal muscle
Sm - different types of contraction initiators?
Mechanical - myogenic reflex, passive stretching - open calcium channels
Electrical - ach or noradrenaline - depolarisation - ca2+ channels open
Chemical - hormones bind to receptors on pm. Second messenger pathway eg (IP3, g protein coupled, NO-cGMP pathways)
Smooth muscle cells in bv and uterus?
Secrete ct matrix.
Perinuclear zone - rer and golgi
Synthesise - col type 3+4, proteoglycans, elastin, adhesive glycoproteins
Sm surrounded by?
External lamina, except at gap junctions
Multi Adhesive glycoproteins(4). Which type of unassumed cells can synthesise?
Sm cells
Osteopontin - bone - bind oateoclasts,ca and hydroxyapatite
Laminin - basal lamina of all epithelial cells
Tenascin - embryonic mesenchyme, wounds, tumours, musculotendinous junctions - modulation of cell attachment to ecm
Fibronectin - ecm tissue, cell adhesion
Smooth muscle cells and t system?
Contraction of sm regulation?
No t system.
Regulation by calcium, calmodulin, myosin light chain kinase system.
Camincrease bind to calmoduline. Activate mlck. Phos of light chain in myosin, expose binding site of actin on myosin head.
Sm contraction maintained?
Long periods - latched state. Comparable to rigor mortis of skeletal muscle
Bv - maintain contraction
Sm specialisation?
Slow prolonged - contraction, extended period.
no fatigue
No nervous stim = spontaneous contractile activity
Other hormones stim sm contraction? Oxycytocin, adrenal med ~ epinephrine(nor)
Sm tissue shape, where found? Structural aspect?
Elongated fusiform. Nucleus central.
Gi tract, male genital system,
Ovary medulla
No myofibrils - no striations - infoldings of sarcolemma - caveolae - also found in cardiac muscle.
Sm int filaments function
Vimentin and desmin - help contraction - pulling ends - shortening cell
2 types of sm innervation!
Single - 1 axon innervates sm in an area - gap junctions
Multiunit - multi axons innervate axons in an area
Regenration of muscle cells?
Skeletal - satellite cells
Cardiac - none
Sm - mitosis eg( uterus, bv, stomach and colon,
Sm cells can develop from?
Fibroblasts, endothelial cells, pericytes
Which cells of seminiferous tubules of testis have contractile function?
Myoid cells
