Week 1 - Bone Structure, Formation, & Modelling/Remodelling Flashcards by Chelsea V

What are the main functions of bone?

Support & protects vital organs
Muscle attachment
Hematopoiesis
Mineral Reservoir - Ca & PO4

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Histologically, what differentiates bone from other tissue?

Mineralized ECM

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Briefly describe the composition of bone matrix

35% organic materials “Osteoid” –> Type I Collagen, glycoproteins, growth factors, cytokines
65% inorganic materials –> hydroxyapatite, other elements
specialized bone cells –> osteoprogenitor, osteoblasts, osteocytes, osteoclasts

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What is the outer surface of bone called?

- Describe its structure

Periosteum - two layers:

Outer layer: connective tissue (fibroblasts, collagen, blood vessels)
Inner layer: cellular layer (osteoprogenitor & osteoblast cells) –> has “bone-making potential”

anchored to the bone by collagen (Sharpey) fibres

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What is the inner lining of the bone called?

Endosteum

- one cell layer thick (progenitor, matrix-secreting, and bone-lining cells)

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What are endosteal cells?

osteoprogenitor cells + bone-lining cells

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What is found in the red marrow of bone?

Blood cells/vessels & supporting reticular meshwork

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What is found in the yellow marrow of bone?

Mainly fat cells (especially in adults)

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What are the functions of osteocytes?

Maintain bone tissue
Communication (with osteocytes & osteoblasts)
Regulation of Ca2+

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Osteoprogenitor cells have the potential to develop into what?

osteoblasts
chondroblasts
fibroblasts

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What are trabeculae?

Developing bone spicules

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What is the function of osteoblasts?

Build bone:

secrete Type I collagen & bone matrix protein
calcify/mineralize the bone

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What is the process of osteoblasts becoming osteocytes?

Osteoblasts secrete matrix, then get surrounded in that matrix, then become osteocytes “sentinel cells” which exist in lacuna

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How/from what does an osteoclast develop?

Common myeloid progenitor
 --> monocyte progenitor
 --> osteoclast precursor
(must be activated by RANKL - from stromal cell or soluble secreted RANKL from activated T-lymphocytes )
 --> inactive osteoclast
 --> resorbing osteoclast

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What are the stages of resorption by osteoclasts?

Migration
Attachment & cell proliferation
Degradation of cellular matrix
Removal of degradation products
Apoptosis or return to non-resorbing state

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What is bone modelling?

Bone changes shape based on mechanical forces or physiological influences

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What is bone remodelling?

Bone is renewed to maintain bone strength and mineral homeostasis

How does PTH act on the bone?

stimulates osteoclasts to resorb bone and liberate Ca2+

- reaction to low blood Ca2+

What effect does calcitonin have on the bone?

STIMULATES osteoBLASTS
inhibits osteoclasts
inhibits Ca2+ reabsorption from intestine and in kidney

Does estrogen encourage or discourage bone formation?

Encourages it

lengthens lifespan of osteoblasts
mediates effects of ROS
regulates RANKL-induced osteoclast differentiation
modulates bone-resorbing cytokines

What are some bone-resorbing cytokines?

IL-1, IL-6, TNF-alpha, M-CSF

What are two types of bone formation/ossification?

Intramembranous

2. Endochondral

What are the main differences between the two types of bone formation/ossification?

Intramembranous - formed w/out cartilage framework & develops into flat bones

Endochondral - formed onto a cartilagenous model & develops into bones of extremeties and axial skeleton which bear weight

What are the stages of intramembranous ossification?

Aggregation (of mesenchymal cells)
Migration (mesenchymal cells)
Formation of 3-D spongy bone network (by osteoblasts)
Formation of periosteum

What are the steps to Endochondral ossification?

1. Develop Hyaline Cartilage Model - mesenchymal cells --> chondrocytes --> secrete matrix - interstitial and appositional growth 2. Develop Bony Collar - becomes periosteum 3 & 4. Death of Central Chondrocytes & Invasion of Blood Vessels - chondrocytes hypertrophy & secrete ALP --> calcification - blood vessels grow through thin bony collar 5. Formation of Primary Ossification Centre = first site where bone begins to form 6. Growth of Endochondral Bone - get epiphyseal cartilage 7 & 8. Secondary Ossification Centres - ossification centres form at proximal and distal end - cartilage is resorbed and replaced by spongy bone 9 & 10. Skeletal Maturity - epiphyseal closure; only remaining cartilage is on articular surfaces

What is an osteon?

The structural unit of bone - formed around a central Haversion Canal (vascular & nerve supply) - contains concentric lamellae, osteocytes (lacunae), and canaliculi (which connect the osteocytes) - grows from the outside in (osteoblasts are central)

Trivia question: What is the last bone to stop growing?

Clavicle (usually around age 21)

Trivia question: What is the densest bone in the animal kingdom?

An elephant's tail

What is the process for increasing length of a bone?

Proliferation of cartilage at epiphyseal plate | Metaphysis needs to be reshaped to form new diaphysis (b/c head of bone will be further from centre.

How is remodelling cortical bone different than remodelling spongy bone?

Cortical bone is arranged in osteons. | Spongy bone is arranged in trabeculae.

What are the phases of bone remodelling?

1. Activation (recruiting osteoclasts) 2. Resorption (by osteoclasts) 3. Reversal (switch from resorption to osteoblast activity) 4. Formation (by osteoblasts)

What is Wolff's Law?

Bone will adapt to the loads placed on it

Why is bone the "best" tissue in the body?

- it heals itself with its own tissue - it renews itself with its own tissue - it responds to the demands placed on it

Where are different types of marrow located within bones in an adult?

``` Yellow marrow (fat) is located in the medullary cavity in spongy bone in diaphysis of long bones. Red marrow (hematopoietic) is located in flat bones and epiphysis of long bones. ```

What is the physis? | What is another name for this?

Growth plate | aka. epiphyseal plate

What is a Salter-Harris Type I Fracture?

No bone injury but growth plate detaches

What is a Salter-Harris Type II Fracture?

Fracture proximal to growth plate with a portion of metaphysis breaking off with the head of bone.

What is a Salter-Harris Type III Fracture?

Fracture where chunk of epiphysis and physis comes off

What is a Salter-Harris Type IV Fracture?

Fracture goes straight through epiphysis, physis, and metaphysis.

What is a Salter-Harris Type V Fracture?

CRUSH INJURY! Physis loses functionality.

What are cement lines?

Uncalcified matrix with little collagen that forms around osteons/new haversion systems - cement the new new haversion system to older osteons