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MSK I > Histology of the Bone > Flashcards

Histology of the Bone Flashcards

1
Q

general features of bone

A

Cells, fibers, ground substance

contains extracellular matrix consisting of hydroxyapatite

dynamic: undergoes constant remodeling in response to chronic stress

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2
Q

general features of bone

A

mechanical support, locomotion, support, storage of calcium and phosphate ions

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3
Q

bone architecture: compact bone versus spongy bone

A

compact bone is called lamellar; encloses inner spongy layer

spongy bone is called trabecular or cancellous bone
lamellar or woven with spaces for bone marrow
have trabeculae

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4
Q

Long bones are ___ and include these two bones:

A

tubular, humerus, femur

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5
Q

Short bones are ____ and include these bones

A

cuboidal, ankle and wrist

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6
Q

Flat bones are ____ and include

A

protective, cranium

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7
Q

Irregular bones are ____ and include

A

various shapes, include the pelvis

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8
Q

sesamoid develop in ____ and an example is the

A

develop in tendons

patella

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9
Q

Diaphysis

A

the “shaft” compact bone surrounding marrow cavity

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10
Q

Epiphysis

A

ends of the bones

spongy bone surrounded by compact bone

contains growth plate or epiphyseal plate

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11
Q

Metaphysis

A

spongy bone between the end of the diaphysis and the epiphysis

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12
Q

periosteum

A

connective tissue covering the bone

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13
Q

endosteum

A

connective tissue lining the marrow cavity of the bone

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14
Q

which area contains the epiphyseal plates?

A

epiphysis

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15
Q

which bone area connects tissue lining of the marrow cavity?

A

endosteum

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16
Q

Connective tissue of the periosteum and endosteum

cell types, protein

fiber types

innervation/vascularization

limitations of periosteum

A

fibroblasts and collagen in the outer layer
Sharpey’s fibers = periosteal fibers that penetrate the bone matrix

osteoprogenitors cells line the inner layer
osteoprogenitor cells are also contained in the endosteum

note: osteoprogenitor cells become osteoblasts)

periosteum = highly vascularized + nerve supply

periosteum does not cover articular surfaces

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17
Q

what is a common injury associated with periosteal inflammation?

A

shin splints

“medial tibial stress syndrome”

it is an overuse injury

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18
Q

Lamellar bone

A

contains a regular, circumferential arrangement of collagen fibers

Haversian systems (osteons) structural unit

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19
Q

Haversian systems

A

Osteons

unit of structure in lamellar bone

circumferential arrangement of collagen fibers

lacunae are the spaces for cells (osteocytes) within the lamellae

Lacunae are the spaces for cells (osteocytes) within the lamellae

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20
Q

osteocytes are located in

what are osteocytes

A

lacunae within osteons

mature or differentiated osteoblasts

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21
Q

Canaliculli =

A

small canals that radiate from the lacuna and “house” cell processes

blood vessels occupy the central canal of a Haversian system

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22
Q

Osteons =

A

concentrically arranged lamella around a central haversian canal

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23
Q

what are in the haversian canal?

A

blood vessels

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24
Q

How do blood vessels get into the lamella?

A

Blood vessels from periosteum enter the lamella through Volkmann’s canal, perpendicular to the diaphysis, and branch to enter into Haversian canals

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25
Q

in the adult, what cells and where are these cells located when bone repair is required?

A

osteoprogenitor cells in the endosteum which differentiate into osteoblasts

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26
Q

from outside in

A

periosteium outer later (collagen, blood vessels, Volksmann canals) –> periosteum inner layer (osteoprogenitor cells) –> endosteum (osteoprogenitor cells and Volksmann canals) –> lamella with Volksmann canals and Haversian systems

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27
Q

Osteocytes

A

maintain bone matrix
solitary cells, usually flattened or spindle shaped

surrounded by mineralized matrix

visually, think spidery looking cells surrounded by extracellular matrix

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28
Q

Osteocyte processes (where are they, how are they connected, and what purpose)

A

in canaliculi and are connected by GAP JUNCTIONS

allows communication and transport of nutrients

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29
Q

interstitial lamella is the result of

A

bone remodeling

30
Q

Bone matrix =

A

organic component = Type I collagen, proteoglycans, chondroitin sulfate, karatan sulfate

inorganic component = calcium phosphate and hydroxyapatite

31
Q

woven bone

A

usually temporary, weaker than lamellar

difference between them is that collagen is not aligned

also found in developing bone

32
Q

osteoprogenitor cells

A

resemble fibroblasts, flattened, usually alone

differentiation regulated by BMP & core binding factor alpha

33
Q

CFBA1

A

core factor binding alpha 1: one of the two differentiation factors required by osteoprogenitor cells for production

the other is BMP

34
Q

osteoblasts

A

differentiated, bone forming cells
ACTIVE cells: basophilic and cuboidal (Squamous cells in inactive bone)

found in association with newly secreted matrix

differentiation controlled by CBFA-1 and RunX2 and osteocalcin

Sox9 directs the differentiation of osteoprogenitor cells into osteoblasts

35
Q

factors that stimulate differentiation of osteoprogenitor cells versus factors that stimulate differentiate osteoprogenitor cell differentiation into osteoblasts

A

BMP, CBFA-1 = osteoprogenitor cells

CBFA-1+RunX2+osteocalcin = transcription factors for osteoprogenitor cell into osteoblasts; Sox9 directs differentiation

36
Q

Osteoblast differentiation: gene required, 1st indicator, and deficiency outcome of 1st indicator

A

OB-specific genes direct differentiation
CBFA-1/Runx2 —> first indicator (tissue marker) of osteogensis

mice deficient of CBFA-1/RunX2 have cartilage skeletons instead of bone

37
Q

what do osteoblasts do

A

they deposit osteoid

38
Q

osteoid

A

osteoblast deposition consisting of:

non-mineralized collagen 1, osteocalcin, osteopontin, sialoprotein

osteoblasts control bone mineralization

39
Q

osteoblasts deposit a lot of matrix and become disconnected from the outer surface of developing bone. what happens to them

A

they become flattened and a lacunae develops around them

40
Q

how do basophils appear under the microscope?

A

basophilic

41
Q

Osteoclasts

A

bone MOs, derived from monocyte-mac progenitor cells

mononuclear phagocyte system

located in Howship’s lacunae
subosteoclastic compartments

42
Q

Howship’s lacunae

A

location of MOs

43
Q

“osteoclasia” translates

A

bone resorption

44
Q

what do osteoclasts “have” intracellularly

A

lots of mitochondria and acidified vesicles

45
Q

which part of the osteoclast has a ruffled boarder

A

the side closest to the bone

46
Q

what does the osteoclast do

A

breaks down mineralized bone with acid

47
Q

osteocytes are actively regulated by what two hormones?

A

calcitonin and PTH

48
Q

Bone formation 1: intramembranous osteogensis occurs in the following sequence (5 steps)

A

Mesenchymal cells aggregate

mesenchymal cells form osteoblasts: bone blastema is formed

bine matrix deposited by cells of blastema, forming primary bone.

ossification centers fuse to form trabeculae (spongy bone)

49
Q

three things to keep in mind about intramembranous ossification that distinguishes it from the other form of bone formation

A

1) develops from a well vascularized primitive connective tissue
2) bone formation is not preceded by cartilage
3) an aggregate of mesenchymal cells differentiates directly into osteoid producing osteoblasts

50
Q

bones formed by intramembranous bone formation include

A

clavicle, frontal and parietal bones, parts of occipital, temporal, mandible, and maxilla bones

51
Q

Endochondral osteogenesis

A

this is when bone replaces a cartiaginous template

chondrocytes in the cartilaginous template become isolated by the extracellular matrix (mostly type II collagen)

52
Q

endochondral osteogenesis beginning with chondrocytes secreting _____ collagen

A

Chondrocytes secrete type X collagen, promoting angiogenesis

increased blood supply promotes calcification of matrix and chondrocytes undergo apoptosis

primary centers of ossification form in the diaphysis and secondary form in the epiphysis

53
Q

How does endochondral ossification begin?

A

Chondrocytes in the cartilaginous template become isolated by the ECM (mostly type II collagen)

chondrocytes then hypertrophy and secrete Type X collagen which in turn promotes angiogensis

blood vessels deliver calcium and promotes general calcification of ECM.

then chondrocytes undergo apoptosis.

primary ossification forms in the diaphysis and secondary centers of ossification form in epiphysis

54
Q

Primary ossification centers

A

occur where proliferation of chondrocytes have hypertrophied and secrete angiotactic factors

55
Q

Secondary ossification centers

A

occur in the epiphyseal sites: vascularization of the epiphysis delivers bone forming

chondrocytes in the epiphyseal plate secretes IHH which promotes chondrocyte proliferation but inhibits hypertrophy

these cells add to the bone in both diaphysis and epiphysis. eventually epiphyseal plate becomes epiphyseal lines and cease growing

56
Q

Reserve Zone

A

hyaline cartilage right under the epiphyseal cartilage

57
Q

Proliferative Zone

A

chondrocytes prolif: VERTICAL LINES or stacks, share a common territorial matrix

58
Q

Hypertrophic Zone

A

Chondrocytes enlarge, secrete Type X collagen and vascular endothelial growth factor
Matrix calcifies
transverse septa are thinner
angiogenesis is stimulated

59
Q

Vascular invasion zone

A

blood vessels invade
osteoprogenitor cells move in
blood vessels transverse septa

osteoblasts beneath the sites of vascular invasion begin to deposit osteoid on the cartilaginous cores forming trabecular bone

60
Q

“osteoclasts chase”

A

the ossification front begins in the vascular invasion zone: chondrocytes are destroyed

61
Q

in which direction do chondrocytes proliferate in the proliferative zone?

A

away from the ossification front, which increases the length of the cartilage

62
Q

proliferating chondrocytes express _____ in the prolifierative zone

A

CFBA-a/RunX2

63
Q

in which direction does the osteoclast chasing/osteocyte running occur?

A

in the direction of the epiphyseal cartilages

64
Q

Unlike intramembranous ossification, endochondral ossification occurs because of

A

chondrocytes at primary ossification centers have secreted type II collagen (hyaline cartilage) which is the template that is eventually replaced by bone

65
Q

where do the osteoprogenitor cells come from in intramembraneous ossification versus endochondral ossification

A

intramembranous ossification center, mesenchymal cells become osteoblasts and directly deposit osteoid

endochondral ossification requires osteoprogenitors imported via vascular supply from the perichondria arrive and are responsible for secreting bone matrix

66
Q

bone remodeling: compact bone remodeling occurs within the

A

osteon

67
Q

a _______ indicates the edge of a remodeled osteon

A

cement line

68
Q

in ________ more bone is resorbed than replaced

A

osteoporsis

69
Q

Activation/Resorption/Reversal/Formation

A

Osteoblasts are recruited in the Haversian canals, differentiate into osteoclasts, which begin resorption of the inner lamella moving outward, leaving “interstitial lamella”

when osteoclasts stop, osteoblasts are recruited and begin depositing osteon (osteoclast/osteoblast reversal)

cement line indicates the boundary of newly organized lamella

70
Q

when a bone breaks…

A

the vascular supply is disrupted: blood clot forms.

haversian system fails to receive blood, it dies.

MOs scavenge/clean area of debris

intense proliferation of osteoprogenitor cells from periosteum and endosteum

osteoblasts form cellular collar around fracture site

immature bone is formed (woven bone)

trabeculae unite to form bony callus that temporarily unite the bone fragments

woven bone is remodeled into lamellar bone

71
Q

endosteum (for real this time) line

A

haversian canals and marrow cavities

72
Q

Shin splits

A

Medial Tibial stress syndrome

periosteum

MSK I (14 decks)

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