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MEDSCI 142 > Musculoskeletal System > Flashcards

Musculoskeletal System Flashcards

1
Q

osteogenic cell

A

precursor -> unspecialised stem cells in mesenchyme (i.e. embryonic connective tissue)
location -> surface of bone in periosteum and endosteum, inside central canals of compact bone
function -> resting layer, normally dormant, but can divide and supply developing bone with bone forming cells (i.e. osteoblasts)

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2
Q

osteoblast

A

precursor -> osteogenic cell
location -> usually in a layer under the periosteum or endosteum, wherever new bone is being formed
function -> active layer, synthesis, deposition, calcification of osteoid, can inhibit activity of osteoclasts

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3
Q

osteoid

A
  • organic extracellular matrix of bone
  • synthesised by osteoblasts prior to mineral deposition
  • mainly collagen (i.e. 70% of osteoid) and proteoglycans, other proteins, water
  • eventually infused with hydroxyapatite (i.e. calcification)
  • at first occurs rapidly, slows down as water (i.e. mobile medium) is displaced
  • makes bone strong but dense, so nutritive fluids cannot freely diffuse through it
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4
Q

osteocyte

A

precursor -> osteoblast
location -> surrounded by bone, trapped within lacunae, long cellular processes inside canaliculi
function -> bone tissue maintenance, canaliculi form live lattice inside bone, can communicate with neighbouring cells, localised minor repair, rapid Ca2+ exchange (i.e. between blood and bone)

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5
Q

osteoclasts

A

precursor -> fusion of monocyte progenitor cells, forms syncytium, can be signalled by osteocytes
location -> at sites where bone resorption is occurring
function ->
- secretes acid and enzymes (i.e. acidic environment activates secreted enzymes)
- dissolves the mineral and organic components of bone (i.e. decalcify → remove organic matter)
- ruffled border increases surface area for secretion and absorption
- forms a pit (i.e. Howship’s lacunae), keeps microenvironment in place
- clear zone adheres osteoclast to lacunae, ensures acid doesn’t escape
- absorbs released components by endocytosis
- releases calcium and phosphate into blood by exocytosis

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6
Q

extracellular matrix of bone

A

resists torsion (i.e. compression + tension)
water -> not well hydrated
fibres -> organic, mainly type I collagen fibres, resists tension (i.e. stretching/pulling)
ground substance ->
- inorganic
- hydroxyapatite (i.e. calcium and phosphate reserve)
- resists compression (i.e. squeezing/crushing)

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7
Q

appositional growth

A
  • adding tissue to existing surface, usually to periosteum
  • chemical signal → osteogenic cells on periosteum divide → form osteoblasts
  • osteoblasts deposit osteoid → calcifies → osteoblasts become trapped in lacunae → form osteocytes
  • when growth stops, osteoblasts can convert back into osteogenic cells or die by apoptosis
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8
Q

bone resorption

A
  • removing bone, usually from endosteum
  • chemical signal → monocyte precursor cells leave blood vessels → start to fuse on bone surface → form osteoclasts → dissolve bone
  • osteoclasts eventually die by apoptosis → resorption stops → blood vessels grow into new space
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9
Q

interstitial growth

A
  • occurs in softer tissues that can deform (i.e. not in bone)
  • cells divide mitotically
  • grows tissue from within → cells divide inside the tissue, secrete more extracellular matrix
  • bone is designed to resist deformation, can only grow by appositional growth
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10
Q

endochondral ossification

A
  • how long bones grow in length, despite articular cartilage on ends
  • epiphysis of long bones can come away from metaphysis, natural break
  • ephiphyseal/growth plate in space, contains hyaline cartilage
  • chondrocytes inside divide (i.e. interstitial growth), increase thickness of plate
  • cartilage and chondrocytes in contact with metaphysis die
  • providing surface for osteoblasts to lay down new bone, and for osteoclasts to remove cartilage
  • eventually rate of cartilage resorption exceeds appositional growth of bone, epiphysis fuses → final bone
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11
Q

lamellae

A
  • layers/sheets of new bone deposited onto a surface
  • typically put down in the same direction within a layer
  • can alternate up to 90 degrees out of phase between layers
  • enables bone to withstand forces from different directions → significantly stronger
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12
Q

unit formation of spongy vs compact bone

A

spongy -> grows outwards into medullary cavity
compact -> grows inwards forming tunnels (i.e. haversian canals)

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13
Q

function of spongy bone

A
  • supports the outer cortex of compact bone in areas where forces occur from multiple directions
  • helps reduce the weight of bone
  • high surface area
  • rapid turnover rate of Ca and P
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14
Q

function of compact bone

A
  • provide strong dense shell of bone on outside
  • thickens areas that are exposed to large forces
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15
Q

primary osteon formation

A
  • formed around existing blood vessel
  • occurs when bone is growing and new bone tissue is being deposited on existing surface (i.e. appositional growth)
  • osteoblasts in active periosteum either side of a blood vessel put down new bone
  • forms periosteal ridges around blood vessel
  • ridges come together and fuse
  • forms tunnel around blood vessel
  • active periosteum becomes active endosteum that lines the tunnel
  • osteoblasts in active endosteum build concentric lamellae onto walls of tunnel
  • tunnel is filled inward toward centre
  • forms new osteon
  • active endosteum becomes resting endosteum
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16
Q

secondary osteon formation

A
  • osteocytes detect damage → releases signal, initiates process
  • monocyte progenitor cells leave blood vessels → attach to surface of old bone → forms group of osteoclasts
  • start boring their way through old bone → forms cutting cone, creating tunnel
  • osteoblasts move in behind the cutting cone
  • line the tunnel wall → form new active endosteum
  • start depositing osteoid onto walls → calcifies → forms new lamella
  • blood vessel grows into newly formed tunnel to supply the cells
  • osteoblast continue to deposit new concentric lamellae onto wall of tunnel → slowly fills it in
  • active area behind cutting cone is called closing cone
  • some osteoblasts are strapped in newly deposited lamellar bone → form osteocytes
  • tunnel is reduced to size of a typical Haversian canal
  • remaining osteoblasts lining Haversial canal either die or become osteogenic cells (i.e. resting endosteum)
  • forms new osteon
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17
Q

function of joints

A
  • movement
  • force transmission
  • growth
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18
Q

functional classification of joints

A

synarthrosis
- immovable joints, high stability
- for growth and force transmission
- commonly found in axial skeleton
amphiarthrosis
- slightly movable, medium stability
- for force transmission
- commonly found in axial skeleton
diarthrosis
- majority of joints
- freely movable, low stability
- commonly found in appendicular skeleton

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19
Q

synovial joint

A
  • a structural classification of diarthrosis
  • not restricted by properties of specific tissues which hold the ends of bones together (i.e. unlike synarthrosis/amphiarthrosis)
  • ends of articulating bones are mostly free (i.e. apart from articular capsule)
  • permits a wide range of motion
  • all have articular cartilage, articular capsule, joint cavity, synovial fluid
20
Q

articular cartilage

A
  • specialised type of hyaline cartilage (i.e. type of connective tissue)
  • protects the end of bone that come together to form a joint
  • absorbs shock and supports heavy loads for long periods
  • provides a smooth, near frictionless surface when combined with synovial fluid
  • contains no blood vessels, nerves or lymphatics
21
Q

cells of articular cartilage

A
  • ~5%
  • chondrocytes
  • build, repair and maintain cartilage
  • live in lacunae
  • occur by themselves or in groups (i.e. nests) depending on the zone
  • nourished by diffusion only
22
Q

ground substance of articular cartilage

A

water
- ~75% of wet weight
- fluid component
- ions and gases dissolve here, provide nutrients to chondrocytes
- can move in and out of tissue
GAGs and PGs
- ~25% of dry weight
- glycosaminoglycans → e.g. hyaluronic acid, chondroitin
- proteoglycans → e.g. aggrecan
- hydrophilic, provides swelling and hydrating mechanism for proper function of cartilage
- part of solid component, fixed inside tissue

23
Q

fibres of articular cartilage

A
  • ~75% dry weight
  • collagen, mostly type II (i.e. flexible)
  • provides structural integrity to tissue
  • has specific zonation patterns
  • tethers surface zone to subchondral bone
  • part of solid component, fixed inside tissue
24
Q

zonation of articular cartilage

A

surface zone
- ~5-10% of thickness
- low proteoglycan content
- fibres arranged in parallel to surface to resist shearing forces
- chondrocytes stuck between fibres → flat and oblong
middle zone
- ~40-45% of thickness
- higher proteoglycan content than surface zone, lower proteoglycan content than deep zone
- fibres in thick bundles, not as densely packed
- round chondrocytes, occur by themselves
- secrete extracellular matrix
deep zone
- ~40-45% of thickness
- highest proteoglycan content
- fibres arranged perpendicular to surface
- round chondrocytes, occur in nests
- secrete extracellular matrix, migrates to upper tissues
tide mark
- between functional zone and transitory zone
- low proteoglycan content
- calcified
calcified cartilage
- low proteoglycan content
- high in hydroxyapatite
- not as calcified as bone
- chondrocytes sit inside lacunae, attached onto calcifying bone
osteochondral junction
- between cartilage and bone
- rich in adhesive proteoglycans
- cement line here

25
Q

proteoglycan complex

A

glycosaminoglycan
- repeating disaccharide unit
- have negative charges
- can be as long as 50 repeating units (i.e. CS)
- e.g. chondroitin sulphate (CS), keratin sulphate (KS)
proteoglycan
- has core protein
- many glycosaminoglycans attached
- negative charges of GAGs repel → stand out like bristles
- e.g. aggrecan (i.e. ~125 CS, ~50 KS)
hyaluronic acid
- very long GAG (i.e. ~25,000 repeating units)
- proteoglycans attach
- form extremely large proteoglycan complex
- attach to collagen fibres

26
Q

loading cycle of articular cartilage

A

unloaded
- negative charges on proteoglycan complexes attract positive ions (e.g. Ca2+, K+, Na+) from synovial fluid → increases ion concentration in matrix of cartilage
- creates an osmotic gradient → draws water and dissolved O2 / nutrients into matrix → cartilage begins to swell
- places increasing tension on collagen fibres → eventually swelling force = tension force (i.e. unloaded equilibrium) → cartilage stops swelling
loaded
- initially densely packed collagen in surface zone impedes fluid movement out
- eventually with sustained pressure, fluid component (i.e. water, dissolved CO2, metabolites and positive ions) is squeezed out into synovial fluid/joint space
- loss of fluid reduces volume of cartilage (i.e. creep) → pushes negative charges closer together
- eventually compressive force = resistive force of solid compartment (i.e. loaded equilibrium) → cartilage stops shrinking

27
Q

fibrous layer of articular capsule

A
  • outer layer of dense connective tissue, both irregular and regular
  • variable in thickness, thicker sections called capsular ligaments
  • made up of parallel but interlacing bundles of white collagen fibres, maintained by fibroblasts
  • continuous with periosteum, can perforate into bone (i.e. Sharpey’s fibres)
  • poorly vascularised (i.e. because of high tension forces, most blood vessels are transitory)
  • richly innervated (i.e. pain and proprioceptors)
  • resist tensional forces, check excessive/abnormal joint movement
  • supports and protects both synovial membrane and joint
28
Q

synovial membrane of articular capsule

A
  • inner layer of loose connective tissue
  • variable thickness
  • lines all non-articular surfaces inside joint cavity (i.e. bc its a fragile layer), up to edge of articular cartilage
  • has villi that increase surface area
    intima
  • thin, ~1-3 cells thick
  • has cells called synoviocytes
  • secretes some components of synovial fluid (i.e. hyaluronic acid, lubricating proteins)
    subintima
  • helps maintain and protect articular capsule during normal movement
  • highly vascular, leakage of filtrate from blood plasma becomes synovial fluid
  • has fibroblasts, don’t put down as much collagen, more reticular and elastic fibres
  • has macrophages, cleans up debris in joint space
  • has adipocytes, packaging, acts like cushions
29
Q

synovial fluid

A
  • clear/slightly yellow fluid
  • amount rarely exceeds 2mL, bc more fluid → larger distance of chondrocytes in cartilage from blood vessels in synovial membrane
  • ultrafiltrate of blood plasma that leaks out of blood vessels in subintima
  • other components secreted by synoviocytes (i.e. hyaluronic acid, lubricating proteins)
  • low concentrations of free cells (i.e. monocytes, lymphocytes, macrophages, synoviocytes)
  • lubricates joints, absorbs shock, metabolisation of chondrocytes, maintains joints
30
Q

function of muscle

A
  • convert chemical energy (i.e. ATP) into mechanical energy
  • movement
  • stability
  • communication
  • control of body openings and passages
  • heat production
31
Q

tendon

A
  • attachment of muscle to bone
  • dense regular connective tissue
  • contains a lot of collagen
32
Q

myofibril

A
  • ~1 micron thick
  • sarcomeres → contractile units
  • Z-disc/line → boundary that separates sarcomeres, pulled closer together during contraction
  • A-band → dark band
  • I-band → light band, Z-disk through centre, shared by neighbouring sarcomeres, shortens during contraction
33
Q

myocyte

A
  • muscle fibre/cell
  • ~10-100 microns thick (i.e. variable)
  • jam packed with myofibrils
  • has multiple nuclei (i.e. syncytium), pushed to the edges of cell
  • sarcoplasm → cell cytoplasm, fills area between myofibrils, contains mitochondria and myoglobin (i.e. O2 storage protein)
  • sarcolemma → fast conductor of action potentials down entire length of myocyte, allows for coordinated contraction
34
Q

endomysium

A
  • loose irregular connective tissue
  • surrounds myocytes
  • contains nerves and capillaries that supply myocytes
35
Q

fascicle

A
  • a bundle of myocytes
  • number of myocytes is variable
36
Q

perimysium

A
  • dense irregular connective tissue
  • surrounds fascicles
  • blend into epi/endomysium
37
Q

epimysium

A
  • dense irregular connective tissue
  • surrounds perimysium and entire muscle
38
Q

deep fascia

A
  • dense regular/irregular connective tissue
  • underlies skin and superficial fascia
  • makes up outer wall of muscle compartments
  • fuses with periosteum when in contact with bone
  • in most areas epimysium glides under deep fascia, in some areas can act as attachment point for muscle
  • keeps blood vessels in place for muscles to act as venous pump
    investing fascia
  • deeper walls/septa that separate individual muscles or muscle groups
  • intermuscular septa → investing fascia between different groups of muscle
  • interosseous membrane → investing fascia between bones
39
Q

causes of hypertrophy

A

heavy resistance training (i.e. repetitive contraction of muscles to near maximal tension)
anabolic steroids
- variants of testosterone synthesised by pharmaceutical companies
- increased protein synthesis in target tissues (incl. skeletal muscle, bone)
- affects other tissues, causing side effects

40
Q

causes of atrophy

A
  • muscles are not used or stimulated by motor neurons
  • complex pathology of diseases such as heart failure, diabetes, cancer, AIDs
41
Q

satellite cells

A
  • some myoblasts fuse during embyonic stage to form myocytes
  • remaining myoblasts remain as individual cells and become satellite cells
  • satellite cells lie beside muscle fibres, outside sarcolemma, within the same basement membrane
  • the only cells in muscle that can divide and fuse with each other and with myocytes
  • repair any damage that may have occurred, replace muscle fibres that die from old age/injury
42
Q

functions of skeletal muscle connective tissue

A
  • provide the organisation and scaffolding upon which the muscle is constructed, mostly in utero
  • provide a medium for blood vessels and nerves to gain access to myocytes
  • resist tension, prevent excessive stretching and therefore damage to myocytes
  • distribute the forces generated by muscle fibre contraction
43
Q

desmin

A
  • protein that holds Z-lines of adjacent sarcomeres together
  • help align sarcomeres between myofibrils
  • allows sarcomeres to shorten together and pull in unison
  • why myocytes have a uniform striated appearance
44
Q

protein complex

A
  • group of proteins containing dystrophin
  • form bridge between Z-lines of outermost myofibrils to sarcolemma, surrounding basement membrane, and endomysium
  • transmits contractile forces generated by sarcomeres to surrounding endomysium → coordinated contraction of neighbouring myocytes
  • contributes to strengthening of sarcolemma
45
Q
A

MEDSCI 142 (6 decks)

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