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
