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Bone 2 -3 Flashcards

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1
Q

Ossification

A

Bone formation; bone that first appears as woven bone, which is eventually replaced by lamellar bone

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2
Q

Primary ossification center

A

First area to start ossifying
usually during prenatal development
located in diaphysis in developing long bones

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3
Q

Secondary ossification center

A

Appears after primary
usually during postnatal development
located in epiphyses in developing long bones

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4
Q

intramembranous ossification

A

develops from mesenchyme (no cartilaginous precursor)
direct mineralization of matrix secreted by osteoblasts
Flat bones of skull (frontal, parietal, etc), lacrimal, nasal, palatine, vomer, maxilla, mandible

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5
Q

Endochondral ossification

A

Has cartilaginous precursor (template of hyaline cartilage)

  • Cartilage does not become bone! The cartilage model is replaced by bone
  • Use long bone ossification as an example
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6
Q

Intramembranous ossification

A

1) Mesenchyme condenses and is highly vascularized
2) Mesenchymal cells differentiate into osteoblasts
3) osteoblasts secrete bone matrix (osteoid) to form trabecular
4) Trabeculae fuse together to form woven spongy bone
5) The periphery of the spongy bone will be remodeled into lamellar compact bone; deeper bone will be remodeled into lamellar spongy bone

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7
Q

When osteoblast gets surrounded by EC matrix it changes it’s name to

A

Osteocyte and can no longer secrete matrix bc there is no where for matrix to go

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8
Q

Endochondral Ossification Steps

A

1) Hyaline cartilage model is formed
2) Bone collar appears (around diaphysis)
Formed via intramembranous ossification within the perichondrium
Hollow cylinder of bone around the mid portion of the cartilage model
3) Chondrocyte in center hypertrophy, degernate and die. Cartilage matrix is calcified
4) Empty spaces are invaded by the the periosteal bud which is going to bring bring vasculature (vessels), mesenchymal cells, osteoprogenitor cells
5) Osteoprogenitors differentiate into osteoblasts, secrete osteoid on surface of calcified cartilage
6) Bone collar increases in thickness and length, but osteoclasts resorb the calcified cartilage and bone. Results in marrow cavity which will be populated with marrow cells
7) Secondary ossification centers form in a similar manner in the epiphyses

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9
Q

Epiphyseal plate

A

Cartilage remains at epiphyseal plate (to allow for growth in length until adulthood) and at the articular cartilage

Note: epiphyseal plates are hyaline cartilage

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10
Q

Endochondral ossification goal

A

growth in length and in width can occur. Growth in length is only possible while epiphyseal plate is present

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11
Q

Five zones of epiphyseal cartilage:

A

1) Zone of rest/reserve @ epiphysis
2) Zone of proliferation
3) Zone of maturation/hypertrophy
4) Zone of calcification
5) Zone of ossification @ diaphysis

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12
Q

Zone of Rest/reserve

A

Typical hyaline cartilage. Chondrocytes arranged randomly

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13
Q

Zone of proliferation

A

Chondrocytes undergo mitosis and are arranged in columns

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14
Q

Zone of maturation/hypertophy

A

Chondrocytes become enlarged, contain a lot of glycogen (white color) . Chondrocytes secrete alkaline phosphatase (marker of mineralization)

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15
Q

Zone of calcification

A

Cartilage matrix is calcified (purple color)

Chondrocytes are dying/dead due to calcified matrix. Leave empty lacunae

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16
Q

Zone of ossification (primary spongiosa)

A

Osteoprogenitors invade, differentiate into osteoblasts
Osteoblasts secrete matrix (osteoid) on surface of calcified cartilage
Matrix becomes calcified
Osteoclasts remove calcified cartilage and bone
Primary spongia (woven bone) is remolded into secondary spongiosa(lamellar bone)

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17
Q

Bone matrix

A

Very mineralized
Inorganic matter - 65% of dry weight. FOR HARDNESS & RESISTANCE
Consists of calcium and phosphorous (mostly ) also bicarbonate, citrate, magnesium, potassium, sodium

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18
Q

Hydroxyapatite crystals

A

Ca10(PO4)6(OH)2 calcium and phosphorous form

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19
Q

Non-crystalline in bone matrix

A

Calcium phosphate

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20
Q

Dont have a lot of calcium or phosphorous

A

bones won’t be hard

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21
Q

Hydroxyapatite crystals

A

Look like rods along collagen fibrils.

Give bones hardness and compressive strength

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22
Q

Hydratoin shell

A

Later of water around each hydroxyapatite crystal (surface ions of crystals are hydrated)
Facilitates ion exchange between the HA crystals and extracellular fluid B/w mineralized tissue and EC fluid

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23
Q

Bone matrix organic matter

A

36% of dry weight. For flexibility and strength.
Mostly type 1 collagen.
90% of organic matrix gives bone tensile strength
Triple helix, super coiled, typical 67 nm cross banding
Greater number of cross links between molecules than in non-bone tissue

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24
Q

Proteoglycans in organic matter

A

Give bone compressive strength.

Condroitin sulfate and heparin sulfate

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25
Bone matrix noncollageous protein example alkaline phosphatase
may function in mineralization of osteoid | Blood serum levels increase during active bone formation which is used as a marker for bone formation
26
Other noncollageous proteins:
``` Cell attachment molecules: -fibronectin -Thrombospondin -Bone sialoprotein -Osteopontin Growth factors: -Fibroblast growth factors (FGFs) -Insulin-like growth facts (IGFs) -Transforming growth factors )Beta TGF-Beta -Bone morphogenic proteins (BMPs) ```
27
Bone cells which originate from mesenchymal
Osteocyte, osteoblasts, osteogenic cell (osteoprogenitor)
28
Bone cells which originate from meatopoietic (bone marrow, specialized macrophages)
Osteoclast
29
Osteoprogenitor cells
Mesenchymal stem cells on bone surface (inner osteogenic layer of periosteum) active during bone growth, factor repair, bone remodeling Differentiate into osteoblasts (under the influence of TGF beta and BMP)
30
When you need osteoblasts what do you have?
TGF beta and BMP
31
Osteoblasts come from
Osteoprogenitor -> Preosteoblast -> osteoblast Lines surfaces of bone tissue Cannot be surrounded by bone matrix Cuboidal to columnar shape when active in matrix synthesis; more squamous when less active
32
Functions of osteoblasts
Synthesis of unmineralized bone matrix (osteoid) Osteoclas stimulating factos Involved in matrix mineralization
33
If osteoblast is surrounded by bone matrix it becomes
osteocyte
34
if osteoblast is not surrounded by bone matrix it becomes
bone lining cells
35
Osteoblasts can become
osteocytes or bone lining cells
36
Osteoblasts secrete
osteocalcin and alkaline phosphatase
37
Matrix mineralization Steps
1) Osteocalcin and various glycoproteins bind Ca2+ 2) Alkaline phosphatase and other enzymes in the matrix vesicles raise local concentration of PO4 - 3) Calcium phosphate and HA crystals form on matrix vesicles 4) Solid bony matrix is formed
38
In presence of PTH (parathyroid hormone), osteoblasts release..
macrophage colony-stimulating factor (M-CSF) that induces formation of osteoclast precursors
39
What differentiates into osteoclasts
Preosteoclasts differentiate into osteoclasts
40
Preosteoclasts have what on the cell surface?
Have RANK
41
Osteoblasts have what on surface?
RANKL
42
What happens when RANK binds to RANKL on osteoblast?
preosteoclast will mature into osteoclast
43
Release osteoclast-stimulating factor (OSF) does what?
activated osteoclasts to reabsorb bone
44
Osteopontin (OPN)
steals osteoclasts to bone so they can absorb bone
45
Steps to osteoblasts recruiting osteoclasts
1) Osteoblast secrete mCSF to induce the division of osteoclast presursors 2) Has rank ligand which binds to ligand on osteoclast precursor to tell it to differentiate to osteoclast 3) Activates the osteoclast 4) RANKL binds to RANK 5) Secretes OSF and OPN to activate osteoclasts 6) Inhibit osteoclast activity by producing OPG
46
Osteoprotogerin (OPG)
Produced by osteoblasts. Binds to RANKL and blocks RANK b/c when RANK binds to RANKL it will increase osteoclast activity Inhibits differentiation of osteoclast precursors into mature osteoclasts Regulates osteoclast activity
47
What increases rate of absorption aka osteoclasts
M-CSF, RANKL, OSF, OPN
48
What decreases rate of bone resorption
OPG
49
Osteocytes
When osteoblasts surround themselves with matrix, they become osteocytes
50
The space in the matrix for each osteocyte
Called lacuna
51
Tunnels for osteocytes
Osteocytes have long cytoplasmic processes, these are in tunnels called canaliculi (in order to get oxygen and nutrients)
52
Osteocytes nutrients, gas, waste exchange
Can't occur through mineralized matrix. Because osteocyte processes contact each other via gap junctions Exchange using the gap junctions can provide nourishment for a chain of about 10 cells
53
Function of osteocyte:
- Maintain matrix | - Mechanosensory: detect mechanical loading and therefore need for bone increase or decrease
54
Osteoblast is
alkaline phosphatase positive
55
Lining cell
Alkaline phosphatase negative
56
Osteocyte
Alkaline phosphatase negative
57
Osteoblasts become osteocytes. 2 kinds:
1) Surronds itself with bone matrix = osteocyte | 2) Doesn't surround itself with bone matrix
58
Osteoclasts
Derived from bone marrow cells Large, multi-nucleated, mobile Have microvili Sits on Howship's lacuna when bone is removed
59
Howship's lacuna
What osteoclast sits on
60
Bone remodeling (bone will be resorbed)
Done by basic multicellular unit (BMU), a wandering team of cells that dissolves an area of the bone surface that fills it with new bone
61
Remodeling follows which sequence
ART Activation Resporption and reversal Formation and mineralizaition
62
How bone remodeling happens:
1) Activation of BMU 2) Resorption of bone by osteoclasts 3) F Formation of new bone by osteoblasts (process is reversed here and more bone is being added)
63
How does cortical bone remodel?
outside part :note Remodels by osteoclastic tunneling Osteoclastic resorption -> layering of osteoblasts -> formation of lamellae Osteoclasts make up head of cutting cone, following by capillaries then osteoblasts which lay down osteoid will fill the cutting bone Has blood vessel
64
How does spongy bone remodel?
Osteoclastic respiration and osteoblastic deposition of layers of lamellae No osteons are formed (no concentric circles of lamellae around a vessel) No blood vessels
65
Bone remodeling absorption and deposition..
an equal amount of bone respiration and deposition No change in overall bone mass Replace old bone with new bone
66
Bone modeling bone mass
changes in bone mass and changes in bone form changes in size and shape due to resorption and deposition in unequal amounts and on different surfaces Due to development and changes in loading patters
67
Bone growth causes length change because..
cartilage grows here cartilage added by bone here cartilage grows here cartilage replaced by bone here
68
Remodeling growing shaft is remodeled by:
bone being resorbed at epiphyseal plate bone added by appositional growth Bone resorted

Basic Tissues (11 decks)

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