lecture 5: bone Flashcards by jillian Bastidas

bone is hypocellular meaning

has few cells

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bone stains pink because

it is eosinophilic

most ECM is made from collagen, which is positive

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compare cartilage and bone

*Cartilage**
large, rounded cells found in clusters
texture: firm but gel-like, elastic
avascular
low metabolic rate
ECM Type II collagen and Aggrecan (sulfated PG) (negative purple)
permeable
continued growth
*Bone**
ellipsoid, isolated cells encased in mineral, hypocellular
mineralized, hard
vascularized
high metabolic rate
ECM: type I collagen, small PGs, glycoproteins
impermeable
complex structure with capacity for remodeling

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ECM of cartilage vs bone

cartilage: type II collagen and aggrecan (sulfated PG) (make negative- purple stain)

bone: type I collagen, small PGs, glycoproteins (areas to bind calcium, positive- pink stain)

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compare texture of cartilage and bone:

cartilage: firm, gel like, high tensile strength, elastic
bone: mineralized hard

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compare cells in cartilage and bone

cartilage: large, rounded cells, often in clusters, encased in ECM
bone: ellipsoid, isolated cells encased in mineral, more hypocellular

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compare metabolic rate and growth in cartilage and bone

cartilage: low metabolic rate, avascular, capacity for continued growth

bone: high metabolic rate, highly vascularized, complex structure with capacity for remodeling

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% make up of ECM of bone

inorganic : 75% of bone

mineral hydroxyapatite

organic: 25 %

type 1 collagen: 90%

small proteoglycans and glycoproteins: 10%

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type 1 collagen fibril

type 1 collagen molecules form head to tail and have spaces in between that form “hole zone”, gives stripped appearance

hole zones are where calcium deposits

“quarter staggered”

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hole zones in bone is where ___

calcium and phosphate deposits

this brings more calcium and phosphate which allows minerals to grow and fill space in between type 1 collagen molecules

collagen molecules do not mineralize, only space in between that is why bone is at most 50-75% mineralized

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Why is bone at most 50-75% mineralized

collagen molecules do not mineralize, only space in between that is why bone is at most 50-75% mineralized

allows some bending of bones

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two type of bone formation

endochondral ossification

intramembranous ossification

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endochondral ossification is found in what type of bones

axial and appendicular skeleton, some facial bones

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where does intramembranous ossification take place

most cranial bones, periosteal bones

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endochondral ossification

simple explanation

mesenchyme undergo chondrogenesis form

cartilage

cartilage undergoes hypertrophy and degradation and is replaced by trabecular bone (on inside), and bone marrow cavity

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intramembranous ossification

simple explanation

mesenchyme

compact bone (no marrow)

happens on outside of long bones and skull bones

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steps of endochondral ossification

mixed process of endochondral and intramembranous ossification

hylan cartilage blueprint
perichondrium replaced with periosteum (compact bone- intramembranous ossification )
cartilage cells undergo proliferation and hypertrophy, during hypertrophy cartilage cells produce different ECM (matrix that can mineralize)
vessels invade bring cells to breakdown cartilage and make bone
cartilage is broken down by chondroclasts leaving hypertrophic ECM backbone
bone is deposited by osteoblasts onto this hypertrophic ECM backbone
same process happens at ends of bones, growth plate in between
continues until bone fully formed and two sites of ossification fuse

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how does perichondrium change to periosteum

progenitor cells in the perichondrium differentiate into osteoblasts instead of chondroblasts

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how is matrix produced by hypertrophic cartilage cells different

can mineralize

matrix can be invaded by blood vessels (periostial blood)

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what kind of cells are brought into the bone during endochondral ossification

clasts, that eat cartilage cells (chondrocytes) and ECM matrix

osteoprogenitor cells- (differentiate into osteoblasts that make bone)

stem cells that form marrow environment

stem cells that form hematopoetic lineages

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where does cartilage remain after bones are finished growing

what is different about this cartilage?

caps of bone- ends articular surface

no longer has perichrondrium - does not have cells to make cartilage- can not repair or regrow

protects bone

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epiphysis

end of bones

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diaphysis

shaft of bone

periosteum

two layer membrane that covers bone

outer layer: dense irregular connective tissue with blood vessels

inner layer: progenitor cells

inner membrane of bone

endosteum

inner membrane of bone branched- has progenitor cells for bone and marrow stroma

metaphysis

area of bone between epiphysis and diaphysis that contains growth plate and its products (endochondral ossification)- trabecular bone

bone formed by endochondral ossification is called

trabecular spongy cancellous bone **and marrow**

bone formed by intramembranous ossification is called

periosteal cortical dense compact

what is this

endochondral ossification derived bone: trabecular bone (spongy bone)(pink with purple center which is remnants of hypertrophic cartilage) marrow (white with purple red blood cells)

intramembranous ossification

bone used for structural support mesenchymal cells (star cells) differentiate into **osteoblasts** that start to secrete ECM bone matrix (type 1 collagen, small PG and glycoproteins **(osteoid)** as the osteoblasts secrete more ECM, ECM starts to mineralize **(mineralizing osteoid)** osteoblasts get stuck and become **osteocytes** occurs in outward fashion, **concentric rings**

matrix of bone that is not yet mineralized

osteoid

cytoplasmic projections of osteocytes that reach out and touch other osteocytes

filopodia

tiny canals through which osteocyte connect to each other

canaliculi filopodia reach out and touch/ communicate with each other

home of osteocyte

lacuna

filopodia have calcium sensors and are bathed in interstitial fluid which allows for

calcium sensor: monitor EMC and determine if it needs to be broken down or made interstitial fluid: can detect movement and detect pressure/ force put onto bone

cell that breaks down bone

osteoclast (not a connective tissue type- made from hematopoetic cells- similar to macrophage) secrete hydrochloric acid which demineralizes hydroxyapatite removed matrix- forms resorption pit -Howship's lacunae large amount of lysosomes

pit of resorption made by osteoclast

howship's lacunae

primary bone is changed to \_\_\_

secondary bone primary bone gets eaten and deposited in rings to form osteons

IO: primary bone is unorganized, when it is remodeled it forms \_\_\_

secondary bone which is very organized in ring structures called osteons

rings of bone

lamellae

central canal of osteon

haversian canal

what lives in haversian canals

dense irregular connective tissue blood vessels and nerves

`mature secondary bone: other name

lamellae bone

perpendicular canals in bone connect what to what

volkmann's canals connect periosteal vessels, to haversian canale vessels and to bone marrow

in trabecular bone new bone is formed

on outside, follows contour of hypertrophic cartilage underneath

in compact bone, bone is remodeled

by osteoclasts eaten bones and osteoblasts reform bone in a concentric circle (osteon)

flattened, line most bone surfaces, may represent quiescent osteoblasts

bone lining cells

osteoblasts

make bone

osteocytes

mature bone cells non-proliferative, encased in mineral, extensive filopodia, monitor calcium levels and communicate with bone forming( osteoblasts) and bone resorbing (osteoclasts) cells

osteoclasts

break down or resorb bone large **multinucleate,** form monocytic lineage, on bone surfaces

formation of bone

osteogenesis

direct differentiation of mesenchymal cells to osteoblasts which secrete bone matrix

intramembranous ossification

during skeletogenesis

bones increase in width and change their shape primary bone is substituted by secondary

during adult life: bone remodeling

means for bone to adapt to mechanical pressure calcium storage and release mechanism

during pathology: bone remodeling

calcium homeostasis disorders fracture repair

bone remodeling is the balance of ___ and ___ controlled by \_\_\_

osteoblasts (make bone) osteoclasts (eat bone) osteocytes