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Histology > Bone > Flashcards

Bone Flashcards

1
Q

Specialized Connective Tissue with mineralized extracellular matrix

A

Roles:

  • support body mass
  • facilitate movement
  • protect vital organs
  • site of hematopoiesis
  • calcium reservoir
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2
Q

Bone Compared to cartilage

A

Similarities:
- Hard Tissues
- Contain living cells embedded in matrix (lacunae)
- Common mesenchymal progenitor cells
Differences:
- bone heavily vascularized/ cartilage avascular
- Bone access to blood vessels via canaliculi
- Cartilage less calcified, uses long range diffusion

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3
Q

How mechanical stress affects bone structure

A
  • compression and movement required for proper bone remodeling
  • plasticity used by orthodontists to modify position of teeth in jaw
  • loss of bone during space flight or immobilization
  • Piezoelectric potential
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4
Q

Piezoelectric potential

A
  • since bone is crystalized, when you cause stress to it, it will generate an electric potential
  • negative, bone deposition
  • positive, bone reabsorbrion
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5
Q

Non Cellular Bone Matrix: Organic Components

A
  • 25% of total bone mass, mostly fibrous
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6
Q

Fibers

A
  • Non cellular, Organic component of bone
  • Collagen type I
  • provides elasticity, tensile strength
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7
Q

Ground Substance (amorphous)

A
  • Non cellular, organic component
  • Glycosaminoglycans (chondroitin and Keratan sulfates)
  • Glycoproteins
  • Osteoid- newly secreted organic matrix ( not yet fully calcified)
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8
Q

Osteonectin and osteopontin

A
  • Glycoproteins

- anchors minerals to collagen, initiate mineralizaiton and promote crystal formation

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9
Q

Osteocalcin and Bone Sialoprotein

A
  • calcium binding proteins
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10
Q

Non Cellular Inorganic Components of bone

A
  • 50-70% of bone mass
  • provide compressive strength
  • Mainly salts of calcium phosphate in amorphous or crystalline form
  • Crystals- Hydroxyapatite
  • Water represents about 15% of bone mass
  • Hydration shell around hydroxyapatite crystals facilitate calcium exchange with fluids
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11
Q

Decalcification

A
  • Flexible tissue

- Only the organic parts are left

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12
Q

Grinding

A
  • Grind down to the inorganic crystals

- translucent ground sections

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13
Q

Mesenchymal Osteoprogenitor

A
  • Osteogenic cell (stem cell)
  • committed mesenchymal cell
  • Commitment is controlled by Bone Morphogenic proteins
  • Located in inner and outer linings of bone
  • can self renew or differentiate
  • Self renewal: PDGF, TGFB, IGF
  • Differentiation: BMP, VitD3
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14
Q

Osteoblast

A
  • Bone forming cell
  • non dividing cell
  • located on bone matrix surface
  • secrete bone matrix (OSTEOID)
  • High secretory activity shown by abundant RER, Golgi
  • Secretion activated by GH, sex steroids
  • Deposition of osteoid between osteoblast cell layer and existing bone
  • Secrete factors that promote osteoclast activity
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15
Q

Osteocyte

A
  • Terminally differentiated cell
  • Osteoblast that becomes trapped in osteoid
  • in spaces called lacunae
  • extend filopodia (skinny microvilli) in canaliculi (canals connecting cells- gap junctions)
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16
Q

Osteocytic Osteolysis (

A
  • limited calcium release inside lacunae
  • Parathyroid hormone (PTH) increases resorption (chief cells of parathyroid gland)
  • Calcitonin decreases resorption (parafollicular cells of thyroid gland)
17
Q

Osteoclast

A
  • Bone Resorbing Cell
  • Macrophage/monocyte lineage
  • multinucleated: fusion of monocytes promoted by Vitamin D
  • large, non dividing, mobile
  • on bone resoprtive and free surfaces in small cavitations called Howships Lacunae
  • Has a ruffled border
18
Q

Ruffled Border

A
  • Bone Resorption zone inside the Howship’s lacunae
  • cytoplasmic processes
  • surrounded by a ring shape sealing zone (clear zone)
  • Increases surface area for resorption of bone
19
Q

Osteoclastic Osteolysis

A

= bone resoprtion
1)Focal decalcification by acidification (citric acid release, carbonic anhydrase)
2)Extracellular digestion by hydrolytic enzymes (collagenase, acid phosphatase, sulfatase) for proteolysis
- Required for bone remodeling and repair
Regulated by:
- PTH(via osteoblasts): increases resorption
- Calcitonin, estrogens: decreases resorption

20
Q

Periosteum

A
  • Outer surfaces
  • Tough connective tissue membrane
  • Covers bone outer surface (except articular and tendon insertion surfaces)
  • Fibrous periosteum (FP)- outer fibrous layer, highly vasularized
  • Osteogenic periosteum (OP)- inner cellular layer (osteogenic cells, osteoblasts)
  • Attached to bone by collagen fiber bundles- Sharpey’s fibers
  • Point of origin of Volkmann’s canals containing blood vessels
21
Q

Endosteum

A
  • inner surfaces
  • Thin single cell layer (progenitor cells, osteoblasts, and osteoclasts)
  • Lines bone internal surfaces (trabeculae, haversian canals)
  • Important for bone nutrition and maintenance
22
Q

Role of Periosteum and endosteum in bone growth, repair and remodeling

A
  • Both contain osteogenic cells
  • cells that divide (mesenchymal)
  • Cells that can give rise to either osteoblast or chondroblast in function of environment and vasularization
  • commintment is dependent on the presence or absence of blood vessels in the area
23
Q

Bone Proper

A

Organization of collagen fibers in matrix determine the types of bone:
- Woven and Lamellar

24
Q

Woven

A
  • Primary/ immature bone
  • Random disposition of collagen fibrils, amorphous calcium phosphate
  • in embryonic development and bone repair
25
Q

Lamellar

A
  • Secondary/ mature bone
  • Organized disposition of collagen fibers (lamellae), crystalline calcium phosphate
  • Cancellous (spongy)
  • Compact (cortical)
  • comes from remodeling of woven bone
  • Adult bone
26
Q

Cancellous (Spongy) Bone

A
  • Network of irregular lamellae: Trabeculae (spicules)
  • Farge spaces filled with bone marrow
  • Mostly converted to compact bone
  • Exceptions: flat bones, alveolar bone around teeth, short bones, epiphyses and diaphysis of long bones
27
Q

Anastomose

A
  • fusion of trabeculae trapping blood and lymphatic vessels inside canals
28
Q

Compact (Cortical) Bone

A 
- Forms diaphysis of long bones, found as thin layer around epiphyses, forms the tables of skull flat bones
Highly organized bone lamellae:
- Circumferential (outer and inner)
- Harversian systems (osteons)
- Interstitial (areas between osteons)
29
Q

Haversian system

A
  • cylindrical columns of 4-15 concentric lamellae surrounding a canal called haversian canal containing blood and lymphatic vessels and nerves
  • osteons
30
Q

Volkmann’s Canals

A
  • Nutrient canals running at right anlge to the Haversian canals
  • contain blood vessels and nerves of bones
31
Q

Mechanism of Calcification

A

1) Osteoblast secretes the new organic matrix- osteoid
2) Osteoblast secrete factors allowing the subsequent mineralization of the matrix
3) osteoblasts become trapped in their own mineralized matrix: become osteocytes residing in lacunae
4) Osteocyte keeps a limited ability to secrete and reabsorb bone in its lacuna, allowing some bone turnover to occur

32
Q

Alkaline Phosphatase

A
  • Secreted by osteoblasts
  • Promtes accumulation of inorganic phosphate in the osteoid, this is a point of saturation where calcium phosphate precipitates
33
Q

Calcium Binding Proteins

A
  • secreted by osteoblasts in the matrix
  • High affinity
  • osteonectin, osteocalcin
34
Q

Matrix vesicles

A
  • Secreted by osteoblasts in the matrix

- contain pyrophosphate and enzymes that inhibit calcification and allow phosphate release

35
Q

Balance between bone deposition and resorption

A
  • bone deposition- ensure high vascularity - trapping of new vessels during bone deposition and anastamose of trabeculae
  • Bone resorption- allows formation of canals/ marrow cavity
  • required to maintain shape in growing bones
  • Allows bone response to mechanical stress
  • Osteons constantly remodeled
  • Help maintain calcium homeostasis
36
Q

Osteoporosis

A
  • resorption–> deposition–> bone mass loss
37
Q

Osteopetrosis

A
  • deposition–> resorption–> bone mass excess

Histology (25 decks)

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