Slide 10 Flashcards
What are the 4 types of bone structures?
long bones [leg ones]
short bones [like connecting one]
irregular bones
flat bone
What is the composition of bone?
compact bone on the outside = dense and supports well
solid and dense in appearance
spongy bone/trabecular bone on the inside = calcified lattice
needle like structure/space filled
epiphysis = end of long bone
epiphyseal plate = site of bone growth
diaphysis = shaft of long bone [hollow]
Define the composition of the diaphysis
main shaft of long bone
hollow, cylindrical, mostly compact bone/thick
provide strong support without too much weight (since hollow)
Define the composition and function of the epiphysis
present at both ends of the long bone
composed of cancellous bone filled with marrow
provides attachment for muscles and stabilizes joints
What is the articular cartilage? What is hyaline cartilage?
layer of hyaline cartilage that covers the articular surface of epiphyses most outer (exterior) part of the epiphysis
hyaline cartilage: elastic cartilage that cushions jolts so impact does not go on bone directly but absorbed by the hyaline cartilage first
What are the layers of bone from the exterior to interior (2)
periosteum
endosteum
What is the periosteum?
dense, white, fibrous membrane that covers the bone
attaches to the tendons firmly to bones
contains cells that form and destroy bones
contains blood vessels important in growth and repair
contains blood vessels that send branches into bone
essential for bone cell survival and bone formation
basically on the exterior of bone
periosteum
outside
attachment
have blood vessel - vascularization
form and destroy bone units
What is the endosteum for?
thin epithelial membrane that lines the medullary cavity
medullary or marrow cavity: hollow/tube/in the diaphysis/ filled with yellow marrow in adult
What is bone composition in short, flat and irregular bones?
inner portion is cancellous covered with compact bone
space inside cancellous bones of irregular and flat bones are sometimes filled with red marrow
large amounts of red bone marrow are found in flat bones like ribs, pelvis and skull
What is the composition of the extracellular matric of bone? the organic and inorganic component
organic: secreted by bone cells [osteoblasts derived from mesenchymal stem cells] get imprisoned in the matrix
ground substance: collagenous fibers and a mix of protein and polysaccharaides forms gelatinous material
it is important in bone growth, repair and remodelling since it acts as a medium for the diffusion of nutrients, oxygen and metabolic waste
ground substance+calcium = bone rigidity
inorganic;
salts, deposition of hydroxyapatite: contributes to hardness of bones and have crystals of calcium and phosphate
calcium carbonate
resist stress and mechanical deformation
magnesium and sodium are also found in bone
How do you get rigid bones?
ground substance +calcium
What are the four major structures of each osteon?
(tree rings)
lamella: each ring, calcified matrix altered by growth
lacunae: small space containing tissue fluid where osteocytes are located between hard layers [the outermost ring layer of the osteon]
canaculi: ultrasmall canals from the osteocyte and connecting them to each other between lacunae
haversian canal: the centre of the osteon contains blood vessels and lymphatic vessels
What is the structure of cancellous bone?
there are NO OSTEONs but trabeculae needled like bony spicules
nutrients and waste are delivered and removed by diffusion through tiny canaliculi =located on the lines of stress to enhance bone strength
What is the most common difference between cancellous and compact bone?
cancellous: between compact bone common in flat bone, on the inner surface of long bone
What are the 4 types of bone cells?
osteogenic cells: differenciate and develop into osteoblasts
osteoblasts: synthesize and secrete collagen in matrix and become trapped in the matric when it calcifies turning to osteocyte
osteoclasts: stem form macrophages [not osteogenic cells]
How do osteoblasts and osteoclasts differ?
blasts: deposit calcium and make new bone matrix
clasts: break down bone during bone resorption
Define the osteoclasts.
giant multinucleated cells
responsible for bone erosion
developed from stem cells in the bone marrow
attach to bone surface by integrins
have large numbers of mitochondria and lysozyme to breakdown macromolecules
brings about resorption of bone by secreting:
collagenase,
matric metalloproteinase, (destroy ECM such as collagen)
and secretion of lactic and citric acids
Define osteocytes.
translated osteoblast that is (matured) trapped in the surrounding calfiied bone matric
final differentiation state for an osteoblast
How do osteoclast reshape a bone while osteoblasts lay down new ECM on underlying surface?
formation of bone tissues continue throughout life even after growth stops
bone formation and reasboprtion balance each other
How do osteoblast induce osteoclast differentiation?
RANKL is on surface of osteoBLAST = binds to receptor RANK on osteaCLAST precursor cell
leads to differentiation of osteoclast precursor cells and activation of osteoclast resobption of bone
stimulators: parathyroid horone [released from thyroid to trigger Ca release]
inhibitors: estrogen acting via osteoprotegrin = OPG binds and competively inhibits RANKL to bnid to RANK receptor so there is less resorption and osteoclast differentiation
How and why do we need to regulate calcium?
bones: store calcium/reserves
maintain and modulate blood calcium levels
calcium is mobilized and moves in and out of blood during remodelling
formation: Ca removed by osteoblast from blood to deposit in bone
breakdown: osteoclast release calcium into blood and increase circulating levels
controlled by parathyroid hormone, calcitonin and vitamin D
Why?
need positive balance of calcium = for bone growth
adults= usually zero balance
don’t want osteoporosis = negative balance [postmenopausal women]
How does parathyroid hormone regulate Ca?
when plasma is low in Ca
- mobilize Ca from bone
- enhances reabsorption of calcium in kidneys
- stimulates release of calcitriol (increases intestinal calcium absorption into blood)
What is calcitriol?
increases intestinal calcium absorption
stimulated release by parathyroid hormone
How does calcitonin act to lower blood calcium?
opposes PTH
produces when high blood calcium levels
calcitonin released in plasma
- decreases bone resorption
- increases renal calcium excretion
How does vit D (calcitriol) reglate calcium?
absorbed by small intestine as part of the diet or synthesized from UV exposure converting the light to vit D
precursor travels to liver and kidneys via blood
vit D:
increases calcium reabsorption in proximal and distal convoluted tubules of kidney
stimulates osteoblast activity to increase bone mass and calcification
intestine increases synthesis of calcium binding proteins on intestinal cells
disorders of vit D can cause weka bones because less calcium absorption
How can we have calcification?
laying down calcium salts [calcium and phosphorus]
What is the general development of bone osteogenesis?
skeleton forms in a fetus = cartilage
cartilage replaced by calcified bone matrix
constant remodelling and growing bone changes cartilage to adult bone = constant activity by osteoblast and osteoclasts
calcification by laying down calcium salts (deposits)
adult bone sculpting allows bones to respond to stress/injury by changing size and shape and density
exercise stimulates osteoblasts to secrete more collagen which makes bone stronger
What are the two mechanism of bone formation?
intramembranous
endochondral
What is the intramembranous way?
fibrous membranes replaced by bone tissue
- does not begin as cartilage
- starts as dense areas of mesenchymal cells [multipotent stem cells] that differentiate and begin to lay down bone around themselves = forms early spicules
- spongy bone tissue begins to develop at sites in membrane = centers of ossification
- occurs in connective tissue membrane
- migration of mesenchymal stem cells to the site of bone formation an differentiate into osteoblasts and then cluster to make centers of ossification
- osteoblasts secrete matrix material and collagenous fibrils (ground substance)
- mineralization occurs where organic strands once mineralized are called trabecula - red bone marrow forms within spongy bone tissue followed by formation of compact bone outside
How does bone develop through the endochondral development?
begins as cartilage with bone formation from centre to the end
- mesenchymal stem cell migrate to site of eventual bone development
- become chrondocytes=cartilage cells
- differentiate into dense avascular mass
- cartilage forms in the shape of bone
- cartilage is surrounded by periosteum
- osteoblasts differentiate from inner surface of periosteum to make a collar bone
- primary ossification centre forms
- blood vessel enters the cartilage at midpoint of diaphysis
- bone grows LENGTHwise = elongates as cartilage/chrondrocytes
- more cell division produces a new epiphyseal plate
- at the other epiphyseal end, older cartilage is broken down by invading osteoclasts which is replaced by the expandin medullary cavity
What are the four layers of the epiphyseal plate?
zone of proliferaition = cartilage cells/chrondrocytes undergo active mitosis
zone of hypertrophy: older, enlarged cells undergoing degenerative changes associated with calcium deposition
zone of calcification: dead or dying cartilage cells under rapid calcification
ossification zone: matric undergoes calcification
What is a centre of ossification?
where spongy bone tissue begins to develop at the sites within membrane
What are mesenchymal cells?
multipotent stem cells differentiate and being to lay down bone
When do the epiphyseal plates fuse?
around puberty
they remain between diaphysis and each epiphysis until bone growth in length is complete
How does the epiphyseal plates closing vary?
they enlarge and increase in length until puberty
closing varies based on:
- bone type
- person (male/female)
What are the processes of appositional bone growth?
occurs in parallel to the growing bone length
periosteum cells develop into osteoblasts = produce more matrix on outer surface of bone
osteoclasts erode the inner surface to enlarge the marrow cavity
