3. Intramembranous and Endochondral Bone Formation - Sayner

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Organs are composed of what 4 basic tissues?

Muscle tissue

Connective tissue

Epithelial tissue

Nerve tissue

What is bone made up of? (2)

specialized cells (e.g. osteoblasts, osteoclasts) + mineralized extracellular matrix (e.g. protein fibers - collagen)

Bone

Functions (4)

internal support

protects

blood forming elements

reservoir

Ways to visualize bone (3)

X-ray

Ground bone section in Indian ink

must heat it up first to kill all cells and then add ink

H&E

must demineralize the bone first by adding hydrochloric acid (dissolves away all the calcium phosphate minerals)

Bone

Specialized cells arise from what 2 distinct lineages?

Mesenchyme

Hematopoetic

Bone: Specialized Cells

Mesenchymal Lineage

Types of Cells (3)

Osteoprogenitor

Osteoblast

Osteocyte

Bone: Specialized Cells

Osteoprogenitor

derived from what lineage/cells?

how?

characteristic/location?

become what?

Osteoprogenitor

derived from mesenchymal stem cells

Bone morphogenic stem cells (BMPs) stimulate mesenchymal stem cells to differentiate into osteoprogenitor cells

flattened cells that reside on the surface of the bone (bone matrix)

undergo mitotic division and differentiate into osteoblasts

Bone: Specialized Cells

Osteoblast

derived from what?

characteristic/location

functions? (3)

more characteristics (2)

Osteoblast

derived from mesenchymal stem cell

cuboidal cells on the surface of bone

functions:

secrete osteoid/matrix (ECM)!

osteoid not yet calcified!!

initiate bone calcification

when not actively secreting matrix → called bone lining cells - periosteal and endosteal cells (

squamous

)

characteristics:

appositional growth

(NOT interstitial)

only secretes matrix onto existing matrix!!

cytoplasmic extensions

Bone: Specialized Cells

Osteoblast

general fxn and express what?

significance?

When an osteoblast is surrounded by matrix, what happens?

Osteoblast: bone formation (osteoblast = build) and express alkaline phosphatase (AlkP)

serum AlkP correlates with osteoblast activity

it becomes an osteocyte

Bone: Specialized Cells

Osteocyte

formation

when an osteoblast is surrounded by matrix it becomes an osteocyte

Bone: Specialized Cells

Osteocyte

derived from what?

location?

characteristics (2)

Osteocyte

derived from mesenchymal lineage

located in structures, chambers, caves within the tissue known as canali (lacuna = cave)

characteristics:

have cytoplasmic projections/extensions that reside in little tunnels between the matrix (aka canaliculi)

Bone: Specialized Cells

Osteocyte

function (2)

Lacuna and canaliculi are important for the maintenance and health of the tissue

“-blast” meaning

its a secretory cell (matrix)!

osteoblast

fibroblast

etc

explain

label

Bone: Specialized Cells