Week 2 Flashcards
1
Q
what are the components of ECM
A
- collagens
- glycosaminoglycans and proteoglycans
- elastin
- structural glycoproteins
2
Q
what are the molecules involved in ECM function
A
- integrins
- metalloproteinases
- growth factors and cytokines
- transcription factors
3
Q
what are fibrillar collagens
A
form from cross-striated linear fibrils and are major structural components of CT; made of alpha chains
4
Q
what are non-fibrillar collagens
A
form non-linear aggregates, and are further classified based on the type of network they make in the ECM
5
Q
what is the triple helical domain formula
A
(GLY- X-Y)n
(glycine is smallest amino acid- no side chain; center of helix; X & Y often proline and hydroxyproline face outward)
- fibrillar: few or no interruptions; n = ~333 repeats
- non-fibrillar: interruptions
6
Q
_ collagen alpha chains are coiled around each other into a ____ to form a rigid rope like structure
A
3; triple-helix
7
Q
the triple helix structure and stability depends on:
A
proline, hydroxyproline, lysine, hydroxylysine
- large, rigid, cyclic amino acids, unique hydroxylation
8
Q
what are hydroxyprolines essential for
A
thermal stability - form water-bridged hydrogen bonds that stabilize triple helix
9
Q
what are hydroxylysines essential for
A
intra-and intermolecular cross-links that stabilize lateral associations of collagen molecules in fibrils
10
Q
what are the enzymes called that hydroxylate proline or lysine
A
prolyl or lysyl hydroxylases
11
Q
what are essential cofactors in the hydroxylation of proline and lysine residues
A
ascorbate (vitamin C) and ferrous iron
12
Q
what happens in the absence of vitamin C
A
scurvy
13
Q
what are the steps to remember in collagen biosynthesis
A
- hydroxylation
- chain association
- trimerization
- secretion into ECM
- Cleavage of amino (NT) and carboxyl (CT) domains
- Covalent crosslinks
14
Q
what is dermatosporaxis
A
- genetic defect in cattle and sheep causing extremely fragile skin and death shortly after birth
- deficiency in N-protease in skin, resulting in persistence of NT domain
- twisted collages prevent packing of collagen molecules into cylindrical fibrils
15
Q
what are lateral associations of collagen molecules into fibrils stabilized by
A
intra and intermolecular crosslinks
16
Q
what does lysyl oxidase form and what is it
A
- cross links between Lys and/or HydroxyLys residues near CT and NT domains
- Cu +2 dependent enzyme
17
Q
what does interference with lysyl oxidase lead to
A
connective tissue defect called lathyrism
- due to lack of cross-linking and decreased fibril stability
18
Q
what are the possible ways lathyrism can occur
A
- defect in copper metabolism
- mutations in lysyl oxidase gene
- sweet peas, clover (BAPN) -> competitive inhibitor of lysyl oxidase
19
Q
what is type 1 collagen
A
- major protein of ECM
- found in bones, teeth, tendons, blood vessels
- heterotrimer 2 alpha1 chains, 1 alpha2 chains
- chains associate at carboxyl domain and fold into triple-helical molecules
- self-assemble into fibrils - strength and template
20
Q
what is osteogenesis imperfecta
A
- genetic disease
- extreme brittleness of bones
- poor mineralized osteoporosis, joint laxity, blood vessel rupture, blue sclera
- variability in phenotype
21
Q
what is OI caused by
A
mutations in either 2 collage type 1 genes
22
Q
where are the mutations most severe with OI
A
TH domain - will be lethal
23
Q
what is Ehlers-Danlos Syndrome
A
- heterogenous group of connective tissue disorders characterized by:
- joint hypermobility
- skin elasticity and fragility
24
Q
Why do mutations in the TH domain cause most severe phenotype? What is the importance of Gly residues and Gly-X-Y formula?
A
- gly (smallest aa): important to form tightly wound triple helix; if disrupted then the trimer is loosened and affects every other structure
25
What is the function of CT? why less severe than TH domain?
- CT domain is important for forming disulfide bonds that stabilize 3 chains together before trimerization
- if some chains have mutations in CT domain, these mutant chains won't participate, but ones that are normal will participate
26
What happens to the NT domain? why mildest phenotype?
- if right at cleavage junction it affects the CT - hyperflexibility
27
what is haploinsufficiency
- ex: mutation in the CT domain
- CT is needed for alignment and association of 3 alpha chains prior to trimerization
- if mutant alpha chain is unable to participate in chain association, this scenario would result in 50% reduction of trimeric collagens produced
28
what is dominant interferance
- ex: mutation in TH domain
- mutant partially-functional collagen alpha chains still able to compete with normal chains for binding to CT domain
- hybrid molecules can't form stable trimers -> all 3 chains likely degraded via protein suicide
- also 3 mutant chains could trimerize and be secreted in ECM -> interfere with aggregate
29
what are glycosaminoglycans?
- unbranched polysaccharide chains or repeating disaccharide units
- one sugar is amino sugar and other is uronic acid
- highly negatively charged b/c carboxyl and sulfate groups
- found in ECM
30
how are 6 gag groups distinguished
- sugar residues
- type of linkage
- number and location of sulfate groups
31
all but ___ are covalently linked to a protein core to form _______
HA; proteoglycans
32
what is hyaluronic acid (HA)
- simplest GAG
- least neg charge
- highest molecular weight
- not made on protein core
- serves as backbone for cartilage PG aggrecan
33
what is chondroitin sulfate (CS) and keratan sulfate (KS)
- highly neg charge
- components of cartilage PG aggregcan
34
what is dermatan sulfate (DS)
- component of 2 bone PG, biglycan and decorin
35
what is heparin (HN)
- most neg charge
- found in mast cells
- has anticoagulant and antiproliferative properties
- commonly a component of the PG serglycin
36
what in Heparan Sulfate (HS)
- found on cell surfaces in PGs
- regulate cytokine-mediated cell interactions
37
how does a GAG get linked to its core protein
- a link tetrasaccharide is assembled on serine residue
- rest of GAG chain, with repeating disaccharide units is synthesize -> one sugar residue at a time
38
what are the most important 4 PG
aggrecan, decorin, serglycin, syndecan
39
what is aggrecan
- largest PG
- highly neg charge
- major component of cartilage
- forms supramolecular aggregates on HA GAG backbone
- made of chondroitin sulfate and keratin sulfate GAGs
- enables cartilage to withstand compressive force
40
what is decorin
- smallest PG
- constituent of bone
- made of dermatan sulfate GAG
- "decorates" type 1 collagen fibers
- maintains inter-fibrillar space to allow mineralization
41
what is serglycin
- high neg charge
- made by mast cells
- made of heparin GAG
- important anticoagulant and antiproliferative properties
42
what is syndecan
- cell surface PG
- comprised of heparan sulfate GAG
- regulates cytokine-mediated cell interactions
43
what are the steps in aggrecan biosynthesis
- aggrecan protein core made on RER
- transported from RER to golgi
- in golgi, GAG chains are added to protein core one sugar at a time
- molecules transported via secretory vesicles to ECM
- hyaluronan is made on plasma membrane
- in ECM, aggrecan, link protein, and hyaluronan come together to form PG aggregates
44
what percent of calcium exists in the serum? and how is it partioned?
1%
- partitioned into 3 sections (ionized, complexed, proetin-bound)
45
why would serum spontaneously precipitate
- contains more than the minimal concentration of calcium nad phosphate ions needed
- in inhibitor-free permissive environment
46
mineral is deposited in the form of ____
hydroxyapatite
| Ca10(PO4)6(OH)6
47
for mineralization to occur, 2 conditions must be present:
1. permissive environment (nucleation site)
2. lack of inhibitors
48
mineralization can happen anywhere if the environment is ____
permissive
49
what is an example of mineralization inhibitors
matrix Gla proteins
50
why doesn't cartilage mineralize
| (hyaline)
sulfated GAG
| - bind Ca -> they are inhibitors to mineralization
51
how does hypertrophic cartilage mineralize
- during EO, hypertrophic cartilage aquires ability to mineralize and be vascularized b/c the ECM components change
- late hypertrophic cartilage chondrocytes release **matrix vesicles (MVs)** from their plasma membrane into ECM
- MVs provide **nucleation sites** where mineralization first occurs by concentrating Ca and PO4 in MVs
52
what type of collagen is hypertrophic cartilage
Type X
| type 10
53
what are the 4 molecules that matrix vesicles contain that allow mineralization?
- alkaline phosphatase
- annexin
- calbindin
- metalloproteinases
54
what dose alkaline phosphatase do
increases phosphate concentration near MV
55
what does annexin do
forms membrane channels for calcium
56
what is calbindin
calcium binding protein inside MVs
57
what does matalloproteinases do
degrade ECM and inhibitors
58
why does bone ECM permit mineralization
contains calcium binding proteins
| in organic phase
59
what is an osteocyte
master regulator cell of bone
60
bone is mineralized ~50-75% of its volume - this enables bone to serve as a ____-____ ____
weight-bearing organ
| deposited directly proportional to compressional load that it carries
61
what does bone need to undergo in order to adapt to changes in mechnical pressure
remodeling
62
during remodeling, mineral, organic matrix and cells are replaced, this tightly regulated process results from a:
balanced action of osteoblasts and osteoclasts
monitored by osteocytes
63
how is remodeling locally controlled
by cytokines and growth factors
64
how is remodeling systemically controlled
by hormones PTH, VD, and calcitonin
65
what is mechanotransduction
- bone adapts to mechanical pressure
- osteocytes sense changes in pressure and Ca concentrations in bone fluid and respond by secreting cytokines that activate OBs or OCLs
66
what is Wolff's law
normal healthy bone will adapt to the loads under which it is placed
| boned of athletes stronger than non-athlete
67
what are the 3 local coupling factors that regulate remodeling
1. TGFB - transforming growth factor-beta
2. PGE2 - Prostaglandin E.
3. N2O - Nitrous oxide
68
what does FGFB do
tells osteoblasts to make more bone
| it is a cytokine (protein)
69
what does PGE2 do
secreted by OB - activates osteoclasts to begin resorbing bone
| lipid
70
what does N2O do
synthesized by OB - tells OCLs to stop resorbing bone
| gas
71
what is osteoclastogenesis
osteoclast formation
| local and systemic
72
what are the two ways the rate of bone resorption is regulated by
1. controlling ostepclast number
2. regulating osteoclast activity
73
what are the local factors of osteoclastogenesis
- local coupling factors (TFGB, PGE2, N2O) and cytokines are produced by OBs
- cytokines bind receptors of pre-OCLs and promote or inhibit their differentiation into mononuclear OCLs
74
what are the systemic (hormonal) factors of osteoclastogenesis
- PTH and VD activate resorption by stimulating OBs to secrete cytokines and increase # of pre-OCLs
- Calcitonin binds receptors on OCLs and inhibits their activity
- Estradiol inhibits OCLs formation by inhibiting cytokines
75
what happens in post-menopausal women
osteoporosis
- b/c decreased estrogen secretion results in increase pre-OCLs and elevation in bone resorption
76
what are general steps of local and systemic control of bone remodeling
1. systemic signal affect OB to tell it to stop making bone
2. OB secrete facots that act to bring in OCLs/ activate OCLs
3. OCLs secrete hydrochloric acid that degrades mineral
4. stimulates release of factors that tell OB that bone is being resorbed
5. OB secrete other facts that tell OCLs to go away
77
what is osteoporosis
- when resorption is greater that formation
- varied causes
- characterized by osteopenia (reduced bone mass)
- radiographic retection not possible until 30-40% bone loss
- with age bone is lost from everywhere
- postmenopausal women
78
how to prevent osteoporosis
* exercise to increase bone mass
* ingest approprate Ca when young
* ability to take up Ca will decrease with age
* humans need 1 gm Ca/day till 65; then ~2.5 gm/day
79
what is osteopetrosis
- rate of bone formation greater than resorption
- rare heredity disorders -> osteoclast dysfunction
- bones are dense and brittle
- marrow is affected -> hematopoiesis can occur in liver and spleen
- anemia common
- Tx: marrow transplant
80
serum calcium is under strict homeostatic control @ ____
10mg/dl; 2-3mM
81
Ca is an essential ____ for many key biological processes
cofactor
82
Serum Ca2+ concentrations are maintained on a minute-to-minute basis by:
* PTH
* VD
* Calcitonin
* Dietary intake
* Excretion
83
cystolic calcium concentration is in the ____ range
micromolar
84
what does the calcium-ATPase pump do
uses energy to pump Ca++ out of cytosol to the cell exterior or into the ER lumen
85
what does the sodium-driven calcium antiport do
exchanges sodium for Ca++ as Ca++ is being extruded from cell
86
what do calcium pumps in mitochondria do
* not very efficient
* pump Ca++ out of the cytosol when Ca2+ levels are high
87
what do calcium-binding proteins (CaBP) do
- in cell, Ca++ is bound by CaBP (calsequestrin or calmodulin)
- help escort Ca++ out of cell
88
dietary Ca2+ absorption takes place in the small intestine and is about ___% effective
50%
89
the amount of Ca ingested should ___ the amont lost through feces, urine, and sweat
equal
90
what increases Ca absorption in the intestine
1-25-(OH)2-vitamin D
91
what does VD do
- facilitates Ca absorption by activating transcription of a Ca binding protein (calbindin) in intestine
92
what does calbindin do
escorts Ca across the cell and into circulation
93
what is acute hypocalcemia and how is it caused and treated
- severe drop in Ca++ (below 5-6 mg/dl)
- lack of Ca++ in nerve impulse transmission and muscle contraction
- death from failure of cardiac muscle contraction
- tx: IV calcium chloride or calcium lactate
| human - tetany in hand
cow - milk fever
94
what is chronic calcium deficiency
rickets - young animals
osteomalacia - older animals
95
what is rickets
- Ca deficiency during skeletal growth
- ex: chick embryo grown in shell-less culture
96
what is osteomalacia
chronic Ca deficiency in adulthood leads to lameness and spontaneous fractures
97
what is hypercalcemia, an example, and tx
- osteopetrosis
- increase in threshold for nerve and muscle activation
- clinical symptoms: brittle bones, weakness, lethargy
- ex: dairy bulls kept on high Ca diet meant for cows
- tx: IV chloride or lactate
| elevation in serum Ca++ (above 10mg/dl)
98
what is hyperphospatemia
- too much phosphate, not enough Ca
- Ca:P ratio should be 2:1
- deficiency of Ca in presence of access P leads to bone resorption and skeletal defects
| big head disease - horses
twisted snout - pigs
99
explain VD synthesis and metabolism
- made in skin (VD3) and ingestin in diet (VD2)
- undergoes hydroxylations by 1-a-hydroxylase in liver, kidney to form active 1,25(OH)2-VD
- production of active form is dependent on PTH which is released when serum Ca are low
100
what kind of hormone is VD
a steroid hormone
101
what is the mechanism of VD action
- diffuses into cell and binds to VD receptor
- results in conformational change of VDR
- enables VD/VDR complex to bind specific VD regulatory elements in target DNA
- gene transcription and protein synthesis stimulated or repressed
102
what are the 3 target sites of VD and what are the results
1. intestine -> increases CaBP (calbindin) -> increase absorption
2. kidney -> increases CaBP -> increases re-absorption
3. bone -> decreases OB -> increase OCL -> resorbtion
| end result: serum Ca level increases
103
what is PTH
- peptide hormone
- made by parathyroid
- undergoes cleavage
- 84aa active form
- secreted when Iow Ca
- half-life 2-5 min
- receptors on kidney and OB
104
what are two target sites of PTH and what is result
1. kiney -> 1-a-hydroxylase -> VD
2. bone -> decrease OB -> increase OCL -> increase resorption
105
what is calcitonin
- single peptide of 32aa
- secreted as prehormone by C cells in thyroid in response to hypercalcemia
- lowers Ca2+ levels by acting directly on OCL and inhibiting resorption
106
what is PTH-related peptide (PTHrP)
- hormone produced by tumors and by lactating breast
- functions to elevate the blood Ca2+
- competes with PTH for receptor binding
107
explain systemic regulation of Ca
- drop in Ca -> PT gland secretes PTH
- kidney: PTH stimulates production of 1-a-hydroxylase - allows hydroxylation of active form of VD, 1-25-(OH)2D3, Calcitriol
- kidney: 1-25VD stimulates CaBP production and increases re-absorption of Ca2+ from urine
- bone:1-25VD and PTH act on OB; OB signal to OCL to start resorbing bone
- intestine: 1-25VD stimulates CaBP and increases absorption of Ca2+
- result = raise in serum Ca2+
- increase in serum Ca2+ detected by C cells in thyroid, leads to release of calcitonin (CT)
- CT inhibits resorption of bone by acting on OCL
108
what are the causes of osteodystrophies
- temporal imbalances (nutritional, endocrine/hormonal, toxic origins/drugs)
- GI/renal/hepatobiliary dysfunction
109
what can osteodrystrophies affect
- skeletally immature animals during EO and IO (growth)
- during remodeling processes at any age -> specific lesios not specific causes
| diffferent types of metabolic bone disease can manifest in same animal
110
what is the most critical local activator of OCLs
RANKL
111
what is the most critical systemic activator of OCLs
PTH and Calcitonin
112
what are the endocrine clads that produce 2 hormonal regulators (activator and inhibitor) of OCL
Parathyroid - PTH
Thryroid - Calcitonin
113
what are the two most important nutriend minerals and one critical nutrient/hormone regulating skeletal remodeling
| activated by kidney
1. Ca2+ and PO4-
2. active Vit D3
| activated by kidney
114
what is bone modeling
* adaptive process
* architectural change
* growth
* increase in bone length and diameter
* pathologic states (fracture healing, infection, neoplasia)
* bone repair/replacement
| EO
115
what is bone remodeling
| think IO
- contant, throughout life
- physiologic maintenance of skeleton
- replacement of old bone -> new bone
- maintain bone mass
- replace old bone/repair microfractures
- respond to metabolic/nutritional changes
116
what are the 3 most common metabolic osteodystrophies
- osteopenia/osteoporosis
- rickets (immature)/osteomalacia (mature)
- fibrous ostrodystrophies (primary hyperparathyroidism, **secondary hyperparathyroidism** - **renal**, nutritonal)
117
osteopenia/osteoporosis
- osteopenia = decreased bone density or mass
- osteoporosis = clinical syndrome of reduced bone mass manifested by bone pain and pathologic fractures
- bone shape normal but reduced amont of trabecular bone
118
what are the causes of osteoporosis
nutritional
- protein calorie malnutrition
- calcium deficiency
- copper deficiency
physical inactivity (disuse/immobilization)
119
lesions of osteoporosis
- decreased OB activity
- decrease trabecular bone -> decreased compact bone (decreased bone density & increased porosity)
- pathologic fractures & infractions
120
rickets and osteomalacia
- defective mineralization
- affect bone and growth cartilage
- rickets = softening of both bones and growth cartilage
- osteomalacia = softening of bones
121
what are the causes of rickets/osteomalacia
- Vit D deficiency
- phosphorous deficiency (herbivores on phosphorous deficient diet)
122
what are the two phases of bone formation
1. osteoid formation
2. mineral deposition
| in rickets and osteomalacia - osteoid mineralization does not occur
123
rickets and osteomalacia pathogenesis
* reduced mineralization - deposition of large seams of osteoids
* decreased OCL resorption
* growth plate deformities in young animals
124
rickets - lesions
- thickend & nodular physes
125
rickets and osteomalacia lesions
* trabecular bone lined by large seams of osteoid
* cortical bone (deofrmed/bowed, endpstea; surfaces lined by thick seams of osteoid, pathologic fractures -> catastrophic fractures)
126
fibrous ostrodystrophy
pathogenesis
- persistend and extreme increase in PTH
- primary hyperparathyroidism
| rubber jaw, big head/bran dz
127
what are the causes of secondary hyperparathyroidism
chronic renal insufficiency/failure
- super, constituently high PTH
high phosphorous diets
128
pathogenesis of renal secondary hyperparathyroidism
- decreased GFR -> increased PO4
- CaPO4 crystallization -> decreased iCa
- decreased iCa -> increased PTH release
- decreased bone formation
- increased OCL differentiation/activation
- increased FB differentiation > OB differentiation
- OCL bone resorption with replacement fibrosis
| squishy bones
129
what is the function of joints
* locomotion
* stability (bone)
* motion of bone
130
what are the key features of joints
- robust to withstand forces
- smooth, frictionless motion of bony ends
- dampen vibration during impact
131
fibrous joints
articulation between vertebral bodies
132
cartilaginous joints
* hyaline/fibrous cartilage interface
* pubic symphysis
133
synovial joints
* both bone ends articulate via hyaline cartilage
* contained in joint capsule
* synovial fluid
133
synovial joints
* both bone ends articulate via hyaline cartilage
* contained in joint capsule
* synovial fluid
134
what is the structure of a joint
* articular (hyaline) cartilage
* subchondral bone
* synovium/synovial fluid
* joint cpasule
* meniscus
* intra and extra-capsular ligaments (collateral, patellar)
135
what is the function of articular cartilage
- low friction gliding surface
- transmits weight bearing forces to underlying bone
- can withstand high cyclic loads
136
what is the function of subcondral bone
- adaptation to stress (wolffs law, thickening of compact bone of increased stress, alterationto configuration of trabecular bone)
- attenuation of force (compact bone - rigid suport; trabecular bone - elasticity; deformable - changes in rigidity have repercussions)
137
what is the function of the outer layer of the joint capsule
* mechanical stability
* innervation (proprioceptive info)
* produce synovial fluid
138
what are the 2 layers of the synovium and synovial fluid
- subintimal layer
- intimal layer
139
what are the components of the intimal layer of the synovium
- lacks basal membrane
- synoviocytes (Type A - macrophage and B - fibroblast)
140
what is the composition of synovial fluid
* blood plasma
* hyaluronic acid - viscous
* lubricin
* cells
141
what is the function of synovial fluid
* lubrication
* delivery of nutrients to cartilage
* removal of waste from cartilage
* joint homeostasis (cytokines, growth factors, enzymes)
142
what is the functuon of the meniscus
* improve joint geometry for even more loading
* mechanical stability
143
what is the function of peri-articular structures (ligaments)
joint stability
144
what is osteoarthritis
- results in articular cartilahe damage and degeneration
- can start with injury to any pf the parts of joint
- results in injury to all other parts of joint
145
joint acute injury
- unusual
- mis-step or fall
- osteochondral damage
- meniscal damage
- ligament injury
- joint capsule
146
what is chronic joint injury
- most common
- cyclic loading (microdamage, response to loading results in weak areas)
- osteochondral damage
- meniscal damage
- ligament injury
- joint capsule
147
what is the influence of subchondral bone
mechanical
- increase bone remodeling -> increase bone density -> changes deformability
biochemical
- releases inflammatory cytokines
pain
-well inervated
148
influence of synovitis
* inflammation of inner lining of joint capsule
biochemical
* produces inflammatory mediators; cytokines
pain
* well innervated
* effusion
* inflammation of nerve endings
149
what is the influence of soft tissue structures
| meniscus, ligaments
damage
* mechanical instability - stress of articular surface
* produce inflammatory cytokines - cartilage breakdown
* pain - innervated
150
what is subluxation
* incomplete or partial dislocation of a bone in a joint
* results in malalignment of nomral bone or limb axis
* results from severe soft tissue trauma and disruption of ligaments and joint capsule
151
how does osteoarthritis occur and what does it result in
* occurs from injury to any part of joint
* results in secondary damage to other parts of joint
152
what are the clinical manifestations of osteoarthritis
joint effusion
* increased synovial fluid due to inflammation
pain (lameness)
* highly innervated structures (synovium, subchondral bone, intra and extra-capsular soft tissue)
decreased joint range of motion
* body attemps to stabilize joint (fibrosis, osteophytosis - proliferation of joint edges)
