Bone Formation Flashcards
intramembranous ossification is typical where
flat bones
name flat bones - 4
part of mandible
maxilla
occipital
temporal and parietal vones
what does metaphysis mean
head, spongy
what is periosteum
dense ct sheath with osteoprogenitor cells
what is diaphysis
middle
what is epiphyseal line
remnant of epiphyseal plate
where does intramembranous ossification take place
within plates of mesenchymal cells
(derived from mesoderm layer)
describe intramembranous ossification - 1
group of mesenchymal cells differentiate (need signal) into osteoblasts (primary ossification center)
synthesis of extracellular matrix
encapsulation of osteocytes
formation of spicules
what is a bone spicule
piece
made by osteoblasts
or
chewed up by osteoclast
describe intramembranous ossification - 2
several similar secondary ossification centers develop on the periphery
the mesenchymal cells differentiate into periosteum
Ossification centers grow radially and fuse
resulting bone is spongy
describe intramembranous ossification - 3
same concept as primary ossification centers
ossification grows out of sites
makes one sheet of bone by fusing together (like soft spot on baby head)
forms periosteum - eventually fuses to flat bone
describe perichondrium vs periosteum
perichondrium = around cartilage
periosteum = around bone BUt has osteoprogenitor cells
both dense ct
where does endochondral ossification take place
within a piece of hyaline cartilage with a similar shape of bone to be formed
all long bones in body come from piece of hyaline cartilage
what is cartilage surrounded by (endochondral ossification)
perichondrium
Except in future articular surfaces
describe primary ossification center of endochondral ossification - 1
at level of diaphysis
perichondrium is transformed into periosteum which deposits bone = bone collar
describe primary ossification center of endochondral ossification - 2
bone collar prevents diffusion of nutrients
cartilage degenerates (hypertrophy and cell death followed by calcification of ECM)
describe primary ossification center of endochondral ossification - 3
blood vessels invade from perichondrium/periosteum
invade spaces left by the degenerating chondrocytes
pushes through bone collar lengthwise through cartilage and drags periosteum with it - and osteoprogenitor cells which create osteoblasts
describe primary ossification center of endochondral ossification - 4
differentiating osteoblasts divide and secrete ecm
ecm made lengthwise - makes space for future bone marrow canal
chewed up cartilage and lots of bone marrow spicles
describe secondary ossification center of endochondral ossification - 1
take places at epiphysis of the future bone (head)
describe secondary ossification center of endochondral ossification - 2
cartilage degenerates
invaded by blood vessels from perichondrium (transformed into periosteum)
describe secondary ossification center of endochondral ossification - 3
cartilage persists in articular surface and epiphyseal plate
mainly where primary meets secondary
articular surfaces = top and bottom, parts that go into joints
describe bone remodelling
osteoclasts are active in resorption of calcified cartilage and woven bone leading to formation of a hollow marrow
name layers of epiphyseal plate - top to bottom - 5
zone of resting cartilage
zone of proliferation
zone of hypertrophy
zone of cell death
zone of mixed spicules
describe zone of resting cartilage (epiphyseal plate)
chondrocytes
describe zone of proliferation (epiphyseal plate)
flat cells
actively dividing (chondrocytes)
looks like stack of coins
describe zone of hypertrophy (epiphyseal plate)
cells swell with fluid
lacunae swell and then burst = cell death
describe zone of cell death (epiphyseal plate)
dying cells
many osteoclasts, some osteoblasts
calcified cartilage - being chewed up, light coloured area, no cells
describe zone of mixed spicules (epiphyseal plate)
zone of mixed bone
describe how endochondral ossification permits growth in length
growth in length of long bone occurs by proliferation of chondrocytes in epiphyseal plate
rate of chondrocyte proliferation and bone formation = destruction of spicules
the thickness of epiphyseal plate does not change but it is displaced away from middle of diaphysis
results in net growth of length of bone
what are spicules not formed by
not formed by lamellar bone – this type of bone is called spongy bone
does thickness of epiphyseal plate change
NOOOO
it just gets displaced as zone of cell death and zone of mixed spicules are turned over
Epiphyseal plates move further away from each other = how bone grows in length
what is bone growth associated with
partial remodeling - shaping
describe bone growth - 1
growth in length - chondrogenesis
epiphyseal plate works to increase length of long bone until 20 years old
describe bone growth - 2
radial growth - perichondrium
osteoprogenitor cells
overtime, bone on outside = length in head of bone
describe bone growth - 3
formation of new spicules by lateral invasion of blood vessels
primary ossification center - osteoclasts chew up
describe bone growth - 4
remodeling of the funnel - periosteal osteoclasts
osteoclasts chew up and work to remodel funnel
describe bone growth - 5
addition of bone from osteoblasts on periosteal surface
describe bone repair
periosteum is needed in case of breakig a bone
periosteal proliferation –> hyaline cartilage –> newly formed primary and secondary bone –> healed fracture (secondary bone)
periosteum kicks in and makes new hyaline cartilage, but not very sturdy, so doc sets it, new cartilage comes from fibers
then follows same process of endochondral ossification = cartilage –> bone (left with compact bone)
why can bones telescope
hyaline cartilage not strong enougb
describe concentration of calcium in blood
calcemia
Concentrations in tissue and blood must be kept constant
what happens if nutritionally deficient in calcium
decalcification of bones
what can calcium be mobilized by
influence of parathyroid hormone = PTH
describe PTH
activates osteoclasts
acts primarily on osteoblasts –> which stop producing bone and starts secretion of osteoclast stimulating factor (since want to conserve calcium)
describe calcitonin
Hormone
produced by thyroid gland
inhibits bone resorption (osteoclasts)
describe pituitary dwarfism
lack of GH (growth hormone)
2 types of dwarfism
epiphyseal plate does not grow
or mutation (reception issue) and also does not grow (does not work)
describe gigantism
excess GH in youngsters
epiphyseal plate does not stop growing at 20
usually caused by a tumour in thyroid gland
describe acromegaly
excess GH in adults - periosteal growth
if over 20 = epiphyseal plate stops growing but since excess growth hormone so long bones cannot grow anymore but causes long hands and feet
growth occurs up to what age
20 years old in humans
regulated by growth hormone - GH
