Histology > Bone > Flashcards

Bone Flashcards

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1
Q

ECM of bone (ground substance/fibers)

A

fibers: type I collagen fibers

ground substance: mineralized (hydroxyapatite)

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2
Q

articular cartilage

A

on the ends of bone

hyaline cartilage WITHOUT PERICHONDRIUM

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3
Q

Histological examination of bone

A

decide: do you want to see the organic (cells.. de mineralized or inorganic material (ground substance.. calcified) of bone?

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4
Q

to view organic material of bone

A

“Decalcified”

  • decalcify bone via acidic solution or solutions of calcium chelators (EDTA)
  • decalcified bone is compressed into type I collagen and stained (eosinophilic in H/E)
  • ONLY SEE PERIOSTEUM (not endosteum)
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5
Q

to view inorganic material of bone

A

“Ground sections”

  • NO living material
  • sliced dried bone, NOT stained (appears yellow)
  • mineral scaffold shows where stuff (nerves, cells, vessels etc. used to be)
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6
Q

Periosteum

A
  • CT covering of external surface of bone EXCEPT at joints of long bones
  • Dense irregular CT (fibroblasts) = outer layer
  • inner layer = osteoprogenitor cells for apositional growth via osteoblasts
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7
Q

bone composition

A

cells (osteoprogenitor, osteoblasts, osteoclasts, osteocytes) + fibers (type I collagen) + ECM (ground substance – bone matrix– keratin sulfate/chondroitin sulfate + mineral – Ca phosphate (hydroxyapatite))

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8
Q

osteoprogenitor cells

A

give rise to osteoblasts

located in inner periosteum, allow for apositional growth

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9
Q

Sharpey’s Fiber

A

Type I collagen that helps attach bone to periosteum.

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10
Q

Endosteum

A
  • lines all of the inner surfaces of bone (marrow cavity, vascular spaces, haversian/volkmann canals)
  • contains osteoprogenitor cells (bone lining cells)
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11
Q

Osteoprogenitor cells (location + function)

A

location: mesenchyme, endosteum, inner periosteum (called “bone lining cells”
function: differentiate into osteoblasts for apositional growth

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12
Q

osteoblasts

A 
secrete osteoid (type I collagen) which sets up the framework for bone
basophilic because lots of rER (to produce type I collagen + other matrix proteins) 
ALWAYS on outside of the cell (for apositional growth)
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13
Q

osteoid

A

nonmineralized (organic) bone matrix made of type I collagen + proteins

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14
Q

Osteocytes

A
  • osteoblasts that are completely surrounded by mineralized bone matrix
  • only visualized in demineralized stained sections of bone
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15
Q

lacunae in bone

A

where osteocyte cell bodies sit (spaces within the mineralized bone matrix)

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16
Q

canaliculi

A
  • spaces occupied by osteocyte cell processes
  • forms a gap junction allow for transfer of large substances between osteocytes
  • connect lacunae
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17
Q

osteoclasts

A

multinucleated, eosinophilic, ALWAYS on outside of cell

  • produced from the fusion of monocytes
  • degrade and remodel mineralized bone matrix
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18
Q

what breaks down the mineral component of bone

A

HCl (formed from the breakdown of H20 + CO2 –> H+ + HCO3 - and Cl channels in the ruffled border)

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19
Q

what breaks down the organic component of bone?

A

hydrolases from lysosomes in osteoclasts.. break down type I collagen, ground substance + other organic material

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20
Q

howships lacuna

A

resulting depression on the surface of a bone after the mineralized bone matrix is dissolved

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21
Q

how do osteoclasts resorb bone?

A
  • ring seal formed via alpha-v beta-3 integrin (osteoclast) binding to osteopontin (bone)
  • ruffled border (osteoclast infolding) formed
  • carbonic anhydrase in the osteoclast cytoplasm breaks down H20 + CO2 –> H+ + HCO3-;
  • ruffled border hast H+ ATP-ase and Cl- channels that cause the formation of HCl in the ruffled border; HCl goes to degrade the inorganic material (mineral) on the bone that the osteoclast is bound to
  • lysosomes in the osteoclast release anhydrases that function to break down the organic material (type I collagen + ground substance)
  • howships lacuna results
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22
Q

hormonal regulation of bone activity: what happens in Ca 2+ is too low

A
  1. PTH is released from the parathyroid gland
  2. PTH binds to receptors on OSTEOBLAST: causes a). expression of RANK-L (ligand) on osteoblast, b). secretion of M-CSF
  3. M-CSF binds onto monocytes and causes the differentiation into macrophages
  4. macrophages start to express RANK (receptor) and fuse to form an immature osteoclast
  5. immature osteoclast with RANK binds to the osteoblast with RANK-L.. causes the osteoblast to mature
  6. mature osteoclast binds to bone’s osteopontin via alpha-v beta-3 integrin, produces the ruffled border, and causes breakdown of bone to release calcium to increase the serum levels
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23
Q

hormonal regulation of bone activity: what happens if ca2+ is too high

A
  1. calcetonin released from c-cells from thyroid gland
  2. calcetonin binds to receptors on the osteoCLAST and causes osteoclastin inactivation
  3. ruffled border is lost and the osteoclast is released from the bone
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24
Q

organic component of bone ECM

A

lots of type I collagen (fibers) and keratan/chondroitin sulfate (ground substance)… this its basophilic

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25
inorganic component of bone ECM
- calcium phosphate (resembling crystal hydroxyapatite) mineralized - solid environment that resists stress/strain, prevents diffusion of oxygen and nutrients (THUS BONE IS WELL VASCULARIZED/INNERVATED) - this bone can only grow apositionally
26
why is bone well vascularized/innervated
solid inorganic material prevents diffusion of oxygen/nutrients
27
growth in cartilage vs. bone
cartilage: can grow interstitially or apositionally (cannot be repaired) bone: can grown only apositionally (can be repaired)
28
lamellae
- parallel layers of mineralized bone - layers due to organization of type I fibers organized in parallel within one lamellae but not the same direction as the next lamellae
29
outer/inner circumferential lamellae
continuous lamellae layer covering the entire outer or inne surface of compact bone, respectively (outer layer is between bone and periosteum, inner layer is between bone and endosteum)
30
Osteon
-organized parallel to the long axis of the bone in a concentric pattern of many lamellae
31
haversian canal
- a channel center of each osteon | - contains blood vessels, loose CT, and lined with enodsteum (osteoprogenitor cells)
32
interstitial lamellae
fragments of old osteons found between neighboring osteons (NO HAVERSIAN CANAL)
33
what is the size of an osteon limited by?
diffusion of nutrients and oxygen from the haversian canal blood vessels
34
Volkmann's canals
- blood vessels that allow for communication between the marrow and periosteum and the haversian canal of one osteon - oriented perpendicular to the osteon and NOT surrounded by lamellae of bone
35
Spongy bone
- branched spicules/trabeculae of bone extending from compact bone - form a space in the hollow portion of long bones
36
marrow cavity
- space between one spicules in trabecular bone - filled with reticular CT - red marrow present during development-- functions in RBC/WBS formation... in adults adipocytes get organized in it (yellow marrow)
37
what is bone derived from
mesenchyme (embryonic membrane tissue).. intraosseous directly from mesenchyme in endochondral from hyaline cartilage that was derived from mesenchyme
38
from what type of cartilage does endochondral bone form?
hyaline (type II collagen)
39
collagen x
promotes the mineralization of collagen in endochondral ossification
40
what factors promote mineralization of collagen in endochondral ossification
- collagen x | - osteocalcin + alkaline phosphatase
41
what promotes bone vascularization in endochondral ossification
VEGF (vascular endothelial growth factor)
42
what factor helps dissolve cartilage in endochondral ossification
metalloprotease
43
primary center of ossification
A primary ossification center is the first area of a bone to start ossifying. It usually appears during prenatal development in the central part of each developing bone. In long bones the primary centers occur in the diaphysis/shaft and in irregular bones the primary centers occur usually in the body of the bone.` -where the bone collar forms IN DIAPHYSIS
44
secondary center of ossification
the area of ossification that appears after the primary ossification center has already appeared - most of which appear during the postnatal and adolescent years. Most bones have more than one secondary ossification center. In long bones, the secondary centres appear in the epiphyses - chondrocytes hypertrophy and die by apoptosis, the cartilage matrix becomes mineralized, and blood vessels invade into the area EPIPHYSIS
45
epiphyseal plate
- between the diaphyseal (primary ossification) and epiphyseal (secondary ossification) - functions in lenghtening the bone from birth through later adolescence - contains zones: reserve cartilage, proliferation, hypertropy and calcification, resorption
46
Zone of reserve cartilage
- in epiphyseal plate - closest to epiphysis - hyaline cartilage with living chondrocytes in lacunae, surrounded by type II collagen and chondroitin sulfate - basophilic
47
zone of proliferation
- in epiphyseal plate - columns of flat chondrocytes (due to mitosis); chondrocytes closest to reserve layer secrete a facto to maintain chondrocyte mitosis - cells elongate and the factor doesn't reach, so cells begin to hypertrophy
48
zone of hypertrophy and calcification
- in epiphyseal plate - hypertrophying columns of chondrocytes that appear paler staining/white - hypertrophying cells secrete factors to promote mineralization of cartilage matrix and differentiation of osteoprogenitor cells (in blood) into osteoblast - matrix calcifies (becomes more basophilic usually) - empty lacunae can be visualized
49
zone of resorbtion
- in epiphyseal plate, closest to diaphysis (bone marrow + spongy bone) - marks invasion of blood vessels, attracted by VEGF, into the spaces left by the dead chondrocytes (lacunae) - osteoblasts attach to cartilage matrix and deposit osteoid onto the surface of calcified cartilage - CARTILAGE IS REALLY BASOPHILIC AND ACELLULAR, BONE IS EOSINOPHILIC AND CONTAINS OSTEOCYTES
50
how to visualize endo vs. intramembraneous ossification
intramembranous: mesenchyme + spicules endochondral: zones
51
why does height growth cease
gonadal steroird (estrogen, testosterone) lead to the closure of the epiphyseal growth plates.. growth plate completely replaced by bone.. thin line = the plate
52
synovial joint
contains a synovial cavity, articular capsule, and articular cartilage (hyaline cartilage without a perichondrium) -diarthroses (freely moving joint)
53
synovial capsule
space between the articulating surfaces of the bones | contains viscous synovial fluid
54
articular capsule of synovial joints
2 layers: outer fibrous joint capsule + inner synovial membrane
55
synovial membrane
- a layer of the articular cartilage of synovial joints - contains a layer or two of squamous synovial cells that lie over a vascularized CT containing fenestrated capillaries - secretes synovial fluid
56
synovial fluid
- viscous fluid in the synovial capsule - made of hyaluronic acid + glycoproteins - lubricates articular cartilage during movement
57
ostepetrosis
"stone bone" - brittle, easily broken bones - woven bone: bone that hasn't been remodeled into lamellar bone because of lack of competent osteoclasts - lack of osteoclasts results in super dense bone that can be easily broken
58
osteomalacia
"soft bone" - osteomalacia in adults; rickets in juvenile - progressive softening and bending of bones due to lack of mineralization - caused by insufficient vitamin D in diet
59
osteoporosis
- decrease in bone density due to an imbalance between osteoblast and osteoclast activity (more OC) - more frequent in post-menopausal women (decreased estrogen) - estrogen replacement therapy + increased calcium uptake = treatment - bisphosphonates used to inhibit osteoclast activity - resistance based exercise and cardio help prevent continued bone loss in men/women
60
estrogen and bone
inhibitor of osteoclast activity.. | decrease in estrogen (post-menopausal women) leads to osteoporosis
61
fracture repair
1. WBC, fibroblasts, macrophages invade the site of fracture to form granulation tissue 2. tissue replaced by fibrous tissue (cartilage and fibrocartilage) to form fibrocartilagenous callus 3. Periosteal cells cover callus and begin to deposit bone over it ; trabecular bone from each broken end grow to meet eachother and the cartilage ossifies 4. Endosteal cells make more osteoblasts and fill in space of trabeculae 5. steps 3 + 4 = make bony callus (woven bone.. weak) 6. woven bone rep;aced with lamellar bone via remodeling
62
rheumatoid arthritis
- chronic inflammatory disease - disfigurement and severe impairment of mobility - antigen to T-cells in synovial compartment activate macrophages nearby - macrophages produce cytokines that cause thickening of the synovial membrane and replacement of synovial cells by CT - macrophage also secrete metalloprotease that breakdown articular cartilage and bone
63
osteoarthritis
degeneration of articular cartilate allowing direct contact of the epiphyses - occurs with aging - results in joint swelling, disfigurement, and fusion of bones
Histology
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