Bone Physiology Flashcards
functions of the skeleton?
framework and levers
protection
mineral storage
fat storage
production of blood cells
What is bone?
it is a rigid form of connective tissue
contains collagen fibres, GAGs and mineral salts
what are GAGs?
glycosaminoglycans
what makes up 15% of the weight of the bone?
collagen type 1
what makes up 10% of the weight of the bone?
organic matrix
what is the mineral component of bone?
hydroxyapatite
(CaPO4(H2O)6)
what type of bones are there?
long bones, flat bones, irregular bones
long bones?
largely tubular with the majority being dense cortical bone
irregular bones?
more box-like with larger amounts of cancellous bone within thinner cortical shells
flat bones?
thin cortical plates with little cancellous bone between
what does an osteogenic cell develop into?
develops into an osteoblast
what does an osteoblast form?
forms bone tissue
what does an osteocyte maintain?
maintains bone tissue
osteocytes?
principal bone cells are osteocytes
osteocytes found where?
found in small spaces in the mineralised matrix called lacunae
and small canals termed canaliculi connect adjacent lacunae
what do osteocytes surround?
surround Haversian Canals
bone tissue matrix is impermeable to?
impermeable to nutrients
how do osteocytes communicate?
through gap junctions
bone cell layer consists of?
periosteum, endosteum and Haversian canals
Where is bone fluid found?
between bone cell layer and bone substance
what do osteoblasts do?
they synthesise and secrete collagen and other components of the bone matrix
e.g. osteoid
calcium phosphate deposited in osteoid
and alkaline phosphatase (catalysing reaction to produce calcium phosphate)
what is formed by osteoblasts?
calcium phosphate crystals
what do osteoclasts do?
they destroy bone matrix
what are osteoclasts derived from?
from haemopoietic lineage
characteristics of osteoclasts?
multinucleated
capacity to spread over 200 microns
what happens to the end products of the degradation of the bone matrix by osteoclasts?
they are absorbed into osteoclasts before being released into the interstitial fluid
what do osteoclasts do to their subcellular space?
acidify their subcellular space to dissolve CaPO4 and enzymatically digest collagen and other matrix proteins
what happens to osteoblasts when producing calcium phosphate?
osteoblasts become in embedded in mineralised osteoid they created
what happens to osteoclasts as they resorb bone?
they leave behind mitogens (growth factors) to encourage osteoblasts to mature and lay down matrix forming a cement or reversal line that forms the border of the newly remodelled bone unit
what do osteoclasts remove in order to avoid catastrophic failure?
they remove damaged matrix
e.g. stress fractures in athletes, greyhounds, racing horses
THIS ALLOWS REPAIR
how do we ensure that we achieve constant bone mass?
the amount of bone being removed = amount of bone formed
too much osteoblast activity results in?
get osteopetrosis (rare) with very dense bones
too much osteoclast activity?
get osteoporosis e.g. in hormone deficiency
blood supply and nerves of bones?
nutrients artery enters through a nutrient foramen
supplies inner 2/3 of the bone form the endosteum
periosteal vessels supply the outer third approx. of the bone via attachments of muscles and tendons
endosteal side of bone?
woven or cancellous bone housing the bone marrow
blood supply runs parallel to the long axis in cortical bone inside Volkmann’s canals
periosteal side of bone?
outer bone surface also brings blood supply via soft tissue attachments
skeleton in early stages consists of …
cartilaginous structures
endochondral ossification?
ossification starts in the middle of long bones
bone collar forms in the connective tissuem the outer layer of which later becomes the vascularised periosteum
epiphyseal plate
allows elongation of long bones
longitudinal growth of long bones occurs via?
growth plates
appositional growth allows the bone to become thicker
chondrocytes form columns with? /5
Resting or reserve zone
Zone of proliferation
Zone of hypertrophy
Zone of cartilage erosion
Zone of endochondral ossification
resting or reserve zone physeal growth plate?
at the epiphyseal end
zone of proliferation physeal growth plate?
where the chondrocytes multiply
zone of hypertrophy and calcification of physeal growth plate?
where they get bigger and the matrix begins to mineralise
Zone of cartilage erosion physeal growth plate?
where the matrix is removed by chondroclasts and blood vessels invade
Zone of endochondral ossification physeal growth plate?
where bone replaces the removed cartilage and bone elongation occurs
toy breeds will be skeletally mature when?
at about 8 months
giant breeds will be skeletally mature when?
take until they are >14 months
cats mature…compared to dogs?
more slowly taking up to 20-24 months to stop growing
when do growth plates close?
various growth plates close at different times depending on adult size of the breed
growth plate closure or healing defines…
it defines skeletal mature length and thus the adult height of an individual
osteoblasts make bone directly within?
within a membranous fibrous tissue structure
how do skull bones, pelvic and scapular structures form?
form by intramembranosus ossification
Wolffs Law?
bone will adapt to the loads placed upon it - use it or lose it
trabecular struts or plates will form in orientation w/ the largest applied forces within the bone as seen in the femoral neck on the left
intramembranosus ossification - what structure doesn’t it have?
no cartilaginous precursor structure
where does bone form during intramembranosus ossification?
bone forms between two periosteal membranes
what structure forms during intramembranous ossification?
a bilayer of cortical bone within a thin sandwich of cancellous bone between
where does appositional growth occur during intramembranossi ossification?
on outer surfaces
what does bone develop from?
from structures of hyaline of cartilage.
what is hyaline cartilage lined with?
lined with a connective tissue sheath, perichondrium
where does ossification begin on long bones?
ossification begins in the middle region of long bones.
what does ossification of long bones start with?
it starts with the growth of blood vessels into the perichondrium (periosteum)
what does the outer and inner layers of periosteum (that forms during ossification of long bones) consist of?
OUTER: of dense, fibrous connective tissue
INNER: of osteoprogenitor cells at this stage
what does the vascularisation provide for the periosteum of long bones?
provides nourishment for the cells of the periosteum stimulating them to differentiate to osteoblasts
what do the osteoblasts produce and what does this become?
they produce osteoid which becomes ossified and forms the bone collar
how is the bone cavity of long bones formed?
it is formed in the centre of long bones. this occurs by hypertrophic chondrocytes releasing alkaline phosphatase, increasing the conc of phosphate in the cartilage matrix & thus precipitating calcium phosphate crystals = calcification
where do the blood vessels infiltrate during endochondral ossification?
these infiltrate the centre of the calcified matrix; osteoclasts and osteoprogenitor cells are then able to migrate along these, the calcified matrix is then replaced by bone gradually
where does ossification progress to after being done in the centre of the long bone?
progresses towards the ends of long bone, as osteoclasts breakdown tissue in the middle of the bone to form the marrow cavity
What are epiphyseal growth plates?
this is where ossification is spreading from the primary centre and gradually approaches the secondary centres
what do osteoblasts do?
they make bone directly within a membranous fibrous tissue structure
what structure becomes the two cortices of the flat bones during intramembranous ossification?
there are two layers that form bone between them to form two parallel plate of bone - these become the cortices
