wk 11, lec 3 Flashcards
osteogenic cells (stem cells) in bone–>
what are the 2 layers/surfaces in bone
endosteum (inner)
periosteum (external surface)
periosteum (external surface)
made of?
inner cellular layer?
outer fibrous layer: type 1 collagen, fibroblast, blood vessels, perforatings (sharpay) fibers
inner: osteoblasts, bone lining cells, mesenchymal stem cells
endosteum (inner body layer)
covers what?
cells?
covers small trabecular of bony matrix that project into marrow caviities
cells: osteoprogenitor cells, osteoblasts, osteoclasts, bone lining cells
bone matrix is made of
50% inorganic material, mainly calcium
hydroxyapatite, along with bicarbonate, citrate, magnesium,
potassium, sodium, and non-crystalline calcium phosphate
organic: in calcified matrix: mostly type I collagen, proteoglycans, glycoproteins (osteonectin)
osteoblasts are bound to bone matrix via
integrins
form cuboidal cell layer (adherent and gap junctions)
what do osteoblasts produce
and what do they form
organic components of bone matrix (type I collagen, proteoglycan, glycoproteins)
layer of collagen-rich material (osteoid).
what can osteoblasts differentiate into and where do they get entrapped in
After synthesis activity is completed, some differentiate asosteocytes entrapped in matrix-bound lacunae, some flatten and cover the matrix surface as bone lining cells,
and the majority undergo apoptosis.
osteocytes are from
osteoblasts ; that get enclosed in lacunae
maintain calcified matrix, have long dendritic processes
osteoclasts
nuclei? function?
create what?
what attaches them to bone?
what do they pump out to break down bone?
multinucleate; for bone resporption
create depressions in the bone
matrix called resorption lacunae or Howship lacunae.
circular sealing zone (ruffled border)
protons and enzymes
5 types of bone
- long (long diaphysis with enlarged ends/ epiphyses)
- short (cube)
- flat
- irregular
- sesamoid (small bones in tendons or joint capsules)
4 types of bone composition
- woven (newly calcified)
- lamella (remodelled from woven)
- compact (80% of lamellar, cortical bone)
- cancellous (20% of lamellar, spongy bone)
2 types of lamellar bone
compact/ cortical
cancellous/ spongy
woven vs lamellar bone
woven is devloping and growing bones; irregular arrangement of cells and collagen, lightly calcified
lamellar is in adults and parallel bundles of collagen in thin layers (lamellae) and heavily calcified
compact/ cortical vs calcellous/ spongy bone
which part of bones
compact: densely packed, thick outer region of bones (beneath periosteum)
spongy: thin trabecullae, covers the inner region, adjacent to marrow cavities
what are the epiphyses (ends) and diaphysis (shaft) of long bones made of
epiphyses: cancellous/spongy bone with thin layer cover of compact bone
diaphysis: mostly compact bone with thin layer os cancellous bone around marrow cavity
short bones made of what type of bone
core: cancellous/spongy bone
surrounded by compact bone
flat bones made of what type of bone
two layers of
compact bone plates separated by a
thicker layer of cancellous/spongy bone.
2 organizations of compact and cancellous bones
§ Mature lamellar bone
§ Woven bone
woven bone (newly calcium, immature)
random arrangement of type 1 collagen
low mineral conent
high osteocytes
develops 1st in embryo
lamellar bone
multiple layers/ lamellae of calcified matrix, parallel sheets or layer around central canal
organized and alternating arrangement of collagen fibers in lamellae
osteon/ Haversian system in compact bone
central/haversian canal
volkmann canal
lacunae (house what?)
lamellae
cancaliculi (contain what?)
outer boundary?
layers of lamellae around central canal
cental/haversian canal has vessels, nerves, endosteum (gives nutrient and oxygen to cells in osteon)
adjacent osteons communicate via volkmann canals
between lamellae are lacunae (with osteocytes) which are spaces
canaliculi are channels that connect lacunae to each other and contain dendritic processes
outer boundary= cement line
what remains in the osteon/haversian system after osteoclasts partially destroy osteons in bone growth and remodelling
interstitial lamellae = irregularly shaped groups of parallel lamellae
scattered among intact osteons.
trabceulae in what type of bone
they dont have a haversian system
Trabeculae are the structural units of spongy (cancellous) bone. They form a lattice-like network of bony struts and plates, which provide support and help distribute mechanical loads.
NOT IN COMPACT BONE
connective tissue
ECM in bone
originate from
fibers and ground
substance, which includes proteoglycans,
glycosaminoglycans (GAGs), and
glycoproteins like laminin and fibronectin.
embyronic mesenchyme ; mesoderm layer
embyronyci mesenchyme –> bone
what cells that
pluripotent stem cells become
chondroblasts: (into chondrocytes) for cartilage formation
fibroblasts: produce collagen and ECM components
osteoblasts: form bone tissues by secreting ECM
adipocytes: store fat
cells of connective tissue
fibroblasts
plasma cells (antibodies)
lymphocytes
eosinophilic leukocytes (defend against parasites, allergy rxn)
neutrophilic leukocytes (phagocygtose bacteria)
macrophages (phagocytose ECM and debris)
mast cells and basophilic leukocytes (i.e histamine)
adipocytes
fibroblasts in bone ECM
active vs inactive/quiescent
Synthesize and secrete collagen, elastin, GAGs, multiadhesive glycoproteins,
active: irregular branch cytoplasm. RER, Golgi, euchromatic nucleus
quiescent: smaller, spindle shaped, less RER, more heterochromatic nucleus
fibroblasts in adults
rarely divide, but can be mitotic via growth factor
i.e. wound healing, myofibroblasts
macrophages in bone
from monocytes; can phagocytose
mast cells in bone have basophilic secretory granules including
§ Heparin: Acts locally as an anticoagulant.
§ Histamine: Promotes increased vascular
permeability and smooth muscle contraction.
§ Serine proteases: Activate various mediators of inflammation.
§ Chemotactic factors: Attract eosinophils and neutrophils to the site of inflammation.
§ Cytokines: Direct activities of leukocytes and other immune system cells.
§ Phospholipid precursors: Converted to
prostaglandins, leukotrienes, a
mast cells can cause
immediate hypersensitivity rxn –> anaphylactic shock
plasma cells in bones
make antibodies
leukocytes (WBC) in bone
migrate from blood into CT
histogenesis (bone formation)
for which type of bone
woven bone is replaced by lamellar bone (expect in skull, mandible, maxilla)
2 process to make primary/woven bone
what is the difference between
- intramembranous bone formation (no cartilage intermediate)
- endochondral bone formation (cartilage intermediate)
intramemrbanous bone formation
bone from mesenchymal cells; no cartilage intermediate
osteoblasts from mesenchyme and start secreting osteoid
osteoprogeniot cells –> osteoblasts –> make osteoid
in primary ossification center
endochondral bone formation
bone formed from cartilage template –> replaced by only tissue
hyline cartilage eroded and invaded by osteoblasts then start osteoid production
cartilage development: chondroblasts into chondrocytes and peripheral cells into fibroblasts and form perichondrium
capillaries penetrate perichondrium and mesesncymal stem cells become osteoprogenitor –> osteoblasts –> make spicules which enlarge and form thin periosteal bone collar of membrane bone
chondrocyte proliferate and make stacks of flattened cells –> then hypertrophy into round superlaceunae
calcify cartilage between superlacuneae
chondoclasts remove dead chondrocytes and make primary marrow cavity
periosteal bud
ossify
bones formed via intramembranous bone formation
are called? what examples?
membrane bones.
* Flat bones like the frontal and parietal bones
* Mandible and maxilla
* Scapula and clavicle
* The periosteal bone collar of endochondral
bones
steps to endochondral bone formation
- fetal hyaline cartilage model devleops
- cartilage calcifies and periosteal bone collar forms around diaphysis
- primary ossification center forms in diaphysis
- secondary ossification cetner in epiphyses
- bone replaces cartilage, except articular cartilage and epiphyseal plates
- epiphyseal plates ossify and form epiphyseal lines
ossification centers
which type of bone formation?
primary and secondary where?
region between the centers?
when ossification center enlarges and leaves a thin plate with hyaline cartilage in center?
tertiary centers
endochondral bone formation
primary OC: mid diaphysis
secondary: epiphyses
region btwn: metaphysis
Ossification centers enlarge, leaving a thin plate with hyaline cartilage at center= epiphyseal plate
tertiary OC in some bone; form bony tubercles/ ridges for muscle and ligament attachment
first bone to ossify in humans
clavicle
tertiary ossification center
in some bone; form bony tubercles/ ridges for muscle and ligament attachment
region between primary and secondary ossification centers
metaphysis
zones in the epiphyseal plate
resting zone (zone of reserve cartilage)
proliferative zone (chondrocytes divide)
zone of hypertrophy
zone of calcification
zone of ossification (osteoprogenitor cells)
bone remodelling (secondary bone formatioN)
from woven bone into lamellar bone
osteoclasts erode calcified cartilage and primary bone matrix
vessels, nerves and lymphs invade cavity formed by erosion
osteogenic cells deposit
osteoblasts deposit secondary bone in lamellae (stronger, hold load)
remodelling even in adults
bone growth
where to divide to get length and via which hormone
girth via
length and girth
length via chondrocyte division at epiphyseal zone of proliferation via growth hormone (esp, kids)
girth via proliferation and differentiation of osteoprogenitor cells in periosteum inner layer (osteoclasts remove bone from inner surface of diaphysial so marrow cavity is enlarged and can get girth without weight gain)
length and girth via
length via chondrocytes at epiphyseal zone of proliferation via growth hormone
growth via proliferate and differentiation of osteoprogentior cells in inner periosteum
bone repair
fractures cause vessel tears –> hemorrhage and clots
macrophages and fibroblasts
chondrocytes form callus with fibrocartilage and Hyaline cartilage
callus replaced by primary bone from subperiosteal region –> secondary bone
primary vs secondary osteoporosis
Primary osteoporosis refers to reduced bone mass and fractures in postmenopausal women or in older individuals due to age-related factors.
- Secondary osteoporosis results from specific clinical disorders like thyrotoxicosis, glucocorticoid excess, and others.
