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Flashcards in bonedevo Deck (54):
1

primary bone

woven or immature bone

temporary, formed first

2

secondary bone

lamellar or mature bone

forms second

3

What are two processes is bone formed through?

intramembranous ossification

endochondral ossification

4

What bones are formed through intramembranous ossification?

flat bones of the skull, bones of the face

5

When does intramembranous ossification occur?

begins to around 8th week of gestation

6

How does intramembranous ossification proceed?

bone cells (osteoblasts) differentiate directly from mesenchyme, producing osteoid

mesenchyme --> bone

7

How does endochondral ossification proceed?

Mesenchyme is replaced by a hyaline cartilage model that is eventually eroded and replaced with bone

mesenchyme --> hyaline cartilage --> bone

8

What bones does endochondral ossification produce?

long and short bones

9

When does endochondral ossification occur?

hyaline cartilage models visible in 6th week

ossification centers present in all long bones by 12th week

10

What are the steps of intramembranous ossification?

1. Development of ossification center
2. Calcification
3. Woven bone and periosteum development
4. Replacement of woven bone

11

How do mesenchymal cells change during development of the ossification center?

mesenchymal cells become osteoprogenitor cells

go from elongated to rounded
go from eosinophilic to basophilic

now they are osteoblasts

12

What are cells that are trapped in the calcifying osteoid called and where do they lie?

osteocytes, lie in lacunae

13

How is woven bone produced?

small, irregular shaped pieces (called spicules) are increased in size by appositional growth (growth along the surface)

these patches of bone production join

embryonic blood vessels infiltrate spaces between spicules and become red bone marrow

14

How is the periosteum formed?

mesenchyme at periphery of bone condenses

15

What is woven bone replaced by?

lamellar bone, both spongy and compact

(in flat bones, spongy is between two layers of compact)

16

What is a Howship's lacuna?

home to osteoclasts, site of bone resorption/breakdown

17

What are the steps of endochondral ossification?

1. Development of fetal cartilage model

2. Bone collar forms around diaphysis, cartilage of shaft begins to calcify

3. Development of a primary ossification center in diaphysis

4. Development of secondary ossification centers

5. Retention of hyaline cartilage as articular cartilage and epiphyseal plate

18

What type of tissue forms the fetal cartilage model?

mesenchymal cells differentiate into chondroblasts, creating hyaline cartilage

19

How does the fetal cartilage model grow?

both interstitially due to activity of chondrocytes in lacunae and appositionally due to chondroblasts on the surface

20

What surrounds the fetal cartilage model?

perichondrium

21

What happens to the perichondrium as endochondral ossification continues?

perichondrium near mid region of the bone has progenitor cells that become osteoblasts--perichondrium now functions as periosteum

forms bone collar around diaphyseal portion of bone

22

What is the first bone tissue that appears?

bone collar around diaphyseal portion of bone

23

How does the bone collar promote change?

impedes diffusion of oxygen and nutrients to underlying cartilage

24

What happens to chondrocytes in mid region of developing bone?

accumulate glycogen, undergo hypertrophy, produce alkaline phosphatase. then they die. now we have a porous 3D structure of hyaline cartilage

these changes compress matrix, signal it to calcify

25

Is calcified cartilage the same as bone?

No, cartilage is primarily type II fibers while bone is primarily type I

26

What color does calcified hyaline cartilage stain?

blue/purple (basophilic)

27

What color does newly formed bone stain?

pink/red (eosinophilic)

28

What induces the formation of the primary ossification center?

capillaries and osteoprogenitor cells from new periosteum penetrate bone collar, grow into disintegrating calcified cartilage

29

How is woven bone produced produced near primary ossification center?

osteoprogenitor cells differentiate into osteoblasts

30

Does calcified cartilage have cells?

NO (but bone does in lacunae)

31

Where is the primary ossification center found?

diaphysis, cartilage is still at ends of bone

32

When do secondary ossification centers develop?

after birth

33

Where are secondary ossification centers located?

epiphyses

34

How to secondary ossification centers develop?

Same as primary

(chondrocytes grow, cartilage matrix calcifies, chondrocytes die, blood vessels and osteoprogenitors enter spaces)

35

Where is hyaline cartilage retained and why?

ends of the bone (to become articulating cartilage)

metaphysis (to become epiphyseal or growth plate)

36

When does epiphyseal cartilage get replaced by bone?

end of puberty

37

Where is the metaphysis found?

between epiphysis and flared portion of diaphysis

38

How to long bones increase in length during infancy and youth?

endochondral ossification occurring at epiphyseal plate

39

What are the zones of an epiphyseal plate?

Zone 1: Resting cartilage--located next to epiphysis

Zone 2: Proliferating cartilage

Zone 3: Hypertrophic cartilage

Zone 4: Calcified cartilage

Zone 5: Ossification--located closest to diaphysis

40

What's going on in the zone of resting cartilage?

chondrocytes singularly or small groups

no matrix production, no mitosis

41

What's going on in the zone of proliferating cartilage?

chondrocytes in lacunae are undergoing mitosis, actively producing matrix

they look like stacked coins in line w/ long axis of bone

epiphysis is pushed away from diaphysis

42

What's going on in the zone of hypertrophic cartilage?

chondrocytes increase in size, accumulate glycogen

matrix compressed/thinned

43

What's going on in the zone of calcified cartilage?

cartilage matrix calcifies thru formation of hydroxyapatite crystals

chondrocytes die

**this zone stains basophilic

44

What's going on in the zone of ossification?

blood vessels, osteoprogenitor cells and osteoclasts open spaces previously occupied by chondrocytes and produce woven bone (that will be replaced later)

45

Does the epiphyseal plate remain the same width during the growth of an individual?

YES

cartilage growth = bone tissue replacement

(new cartilage produced in zone of proliferation must equal activity in zone of ossification)

46

What is a stupid analogy for how endochondral growth looks?

chondrocytes are being 'chased' by the bone cells up the length of the bone

47

What is the epiphyseal line?

epiphyseal plate closure, bone replaces all of the cartilage (bone cells 'caught up' with chondrocytes)

48

How do you widen bones?

appositional growth

osteoblasts secrete matrix along surface of bone

49

How do you make sure your bones don't get too thick or thin?

rate of activity of osteoblasts on periosteal layer should equal that of osteoclasts on endosteal layer

50

How much of your bone do you remodel every year?

5-10%

51

What determines when remodeling occurs?

negative feedback loop of Ca2+ concentration

52

What controls where remodeling occurs?

mechanical stresses and gravity

53

What happens if there is too much Ca2+ in blood?

parafollicular cells in thyroid secrete calcitonin

osteoclasts (therefore bone resorption) are inhibited

osteoblast activity increases

54

What happens if there is too little Ca2+ in blood?

parathyroid glands secrete parathyroid hormone (PTH)

osteoclasts (and therefore bone resorption) are increased