Lecture 9: Microanatomy of Bone Flashcards
4 methods of classifying bone types
whole bone shape
degree of bone density/porosity
micro texture of bone
embryonic origin
whole bone shape: 4 types
long
short
flat
irregular
3 parts of a long bone
epiphysis
metaphysis
diaphysis = shaft
density/porosity: 2 types
compact
cancellous
compact bone vs cancellous bone (location, function)
compact = outer, strong and dense, resists force
cancellous = deep to compact, spongy, large surface area for storage
functions of bone (4)
framework = structure, support
levers for muscles
hemopoietic tissues, fat storage
store minerals = Ca, K, Mg, P
majority of bone is composed of
inorganic/minerals
bone matrix: 2 components
organic - type 1 collagen
inorganic - calcium hydroxyapatite (Ca, P)
3 cells in bone
osteoblast
osteoclast
osteocyte
periosteum surrounds
bone/external surface
endosteum surrounds
bone marrow cavity
2 types of bone marrow
red
white/yellow
is bone vascular or avascular
vascular
can bone remodel
yes
periosteum and endosteum definition and function
vascularized connective tissue layers that line surface of bone
nourish bone tissue = blood supply
make continuous supply of bone cells for appositional growth
2 layers of periosteum: bone
fibrous - outer layer of dense CT
inner cellular layer - osteogenic cells
endosteum: defining feature
loose CT
monolayer of osteogenic cells and osteoblasts
what kind of bone makes up the shaft/diaphysis of long bones
compact bone
4 lamellar systems of compact bone
outer circumferential
inner circumferential
osteons
interstitial lamellae
which lamellae forms the bulk of compact bone
osteons
outer circumferential lamellae contains what
sharpeys fibers
sharpey’s fibers function
anchor periosteum to bone
what is the outermost region of diaphysis (lamellae)
outer circumferential lamellae
which lamellae encircles the marrow cavity
inner circumferential lamellae
how/when do osteons form
as bone remodels
cylinders of bone removed and replaced with concentric lamellae of bone
2 canals within osteons (compact bone)
central
perforating
central canal of osteon contains
blood vessels and nerves
function of perforating canals (osteon)
connect central canals with each other
micro texture of bone: 2 types
woven/immature
lamellar/mature
woven bone: when is it formed, strength
initial bone formation, fracture repair
poorly organized type 1 collagen
weak
lamellar bone: when is it formed, strength
replaces woven bone
strong and organized
when does lamellar bone replace woven bone (2)
formation of primary bone in newborns
remodeling to from secondary bone/osteons
trabeculae definition and function
interconnecting bony struts (in epiphysis and metaphysis)
provide internal support to bones
spongy and porous
cancellous/spongy bone: formed by, function
formed by trabeculae
high surface area for Calcium ion exchange between bone and blood
what is located between trabeculae (2 options)
marrow (red or yellow)
2 types of marrow
red
yellow
red marrow produces
blood cells
yellow marrow made up of
adipose tissue
osteoblasts functions (2)
form bone ECM
lowers blood calcium levels
osteoblasts become
osteocytes
location of osteocytes
lacunae
osteocytes and osteoblasts derived from
osteoprogenitor cells
when do osteoprogenitor cells differentiate into osteoblasts
periods of growth, remodeling, fracture repair
osteoclasts function
resorption/consumption of bone ECM
osteoclasts derived from
monocyte-macrophage progenitors located in bone marrow
when osteoblasts are inactive they are called
bone lining cells
how do osteoblasts communicate with each other
gap junctions
3 components of bone ECM
type 1 collagen
proteoglycans
glycoproteins
osteiod definition
initial organic compound synthesized by osteoblasts
what does osteoids do
calcify
how do osteoblasts become osteocytes
embed in bone ECM
reside in lacunae
osteocyte function
direct bone remodeling in response to mechanical stimuli
how do osteocytes communicate with each other and with osteoblasts
gap junctions
send cell processes through canaliculi
what are canaliculi
channels in bone
how is bone ECM formed
1 layer/lamellae at a time by osteoblasts
organic portion of bone ECM
type 1 collagen
pale appearance
called osteoid
inorganic portion of bone ECM is added to
osteoid
inorganic portion of bone ECM
made of hydroxyapatitie crystals (Ca bond to glycoproteins)
osteoblasts secrete bone specific alkaline phospatase
bone specific alkaline phosphatase
produced by osteoblasts in inorganic bone ECM
aids in hydroxyapatite formation
how do osteoclasts raise blood calcium levels
resorb bone, endocytose ECM byproducts (calcium) and secrete them into blood
ruffled border definition (osteoclast)
portion in direct contact with bone
clear zone definition (osteoclast)
lacks organelles
ring of cytoplasm around ruffled border
actin ring location, function (osteoclast)
inside clear zone
allows bone resorption to occur
seals off subosteoclastic compartment to prevent damage to surrounding tissue
what is the resorptive compartment of osteoclasts
subosteoclastic compartment
what cells resorb bone ECM
osteoclasts
how is inorganic portion of bone ECM resorbed
protons pumped into resorptive cavity (with ruffled border increasing surface area for transport)
how it organic portion of bone ECM degraded
lysosomal enzymes secreted into cavity (with clear zone sealing off secretions from tissue)
what 2 hormones regulate bone resorbing activity of osteoclasts
parathyroid hormone
calcitonin
parathyroid hormone: function, how it accomplishes function
released by parathyroid gland
PROMOTES resorption, increases blood calcium levels
indirect effect on osteoclasts –> receptors on osteoblasts + osteoblasts produce osteoclast stimulating factor
stimulates osteoclast to increase bone resorbing activity
calcitonin: function, how it accomplishes function
secreted by thyroid gland
SLOWS resorption, decreases blood Ca levels
receptors on osteoclasts (acts on them directly)
inhibit osteoclast to decrease bone resorbing activity
what induces mesenchymal/mesodermal differentiation to cartilage/bone during development
oxygen tension in tissue
mesenchymal differentiation in high O2 environments: process name, requirement
osteoprogenitor cells and osteoblasts to form bone –> intramembranous ossification
need vascularized mesenchyme to supply O2
mesenchymal differentiation in low O2 environments: process name
chondrogenic cells and chondrocytes that form hyaline cartilage
blood vessels grow into cartilage = high O2 environment –> calcify cartilage ECM –> replaced with bone
endochondral ossification
result = highly vascularized bone
2 types of bone ossification processes
intramembranous
endochondral
steps of intramembranous ossification
high O2: mesenchymal cells near blood vessels differentiate into osteoblasts
osteoblasts form bone trabeculae –> ossification centers
trabeculae enlarge, fuse and remodel to form bones with compact bone on external surfaces and trabecular bone + marrow cavities internally
kind of ossification process for flat bones of cranium
intramembranous
steps of endochondral ossification
low O2 environment induces mesenchymal cells to differentiate into chondrocytes that form hyaline cartilage
blood vessels invade cartilage –> induces formation of ossification centers where bone cell migrate and replace cartilage with bone
growth plate remains between epiphysis and diaphysis
growth ends when growth plates are vascularized and replaced with bone
growth plate is made of
sheet of hyaline cartilage
what kind of growth is growth plate responsible for
longitudinal
5 zones of growth plate (superficial to deep)
zone of reserve
zone of proliferation
zone of hypertrophy
zone of calcification
zone of ossification
zone of reserve: growth plate
directs proliferation
zone of proliferation: growth plate
chondrocyte mitosis
zone of hypertrophy: growth plate
chondrocytes enlarge bringing in O2
zone of calcification: growth plate
chondrocytes calcify the ECM
zone of ossification: growth plate
cartilage is replaced with bone
