Bone

Question 0

what is the endosteum and the periosteum?

Answer 0

tissue lining the internal (endo) and external (perio) surfaces of bone containing osteogenic cells

Question 1

what are canaliculi?

Answer 1

thin cylindrical spaces that penetrate the matrix and allows the exchange of materials between osteocytes and capillaries

Question 2

what organic components do osteoblasts synthesize?

Answer 2

type 1 collagen, proteoglycans, and glycoproteins

Question 3

what do active osteoblasts look like compared to inactive?

Answer 3

active: cuboidal/ columnar w basophilic cytoplasm
inactive: flattened w/ less basophilia

Question 4

what is in a lacuna where osteocytes are found?

Answer 4

osteocyte

small amount of ECM non-calcified

Question 5

what is an osteoid?

Answer 5

new uncalcified matrix

Question 6

what is bone apposition?

Answer 6

process of secreting new matrix and calcifying it

Question 7

how to osteocytes communicate?

Answer 7

gap junctions + through exchanging material in the small amount of matrix b/w them

Question 8

what is in a osteocyte?

Answer 8

condensed chromatin
reduced rER
golgi

Question 9

what are the depressions osteoclasts are found in during active resorption?

Answer 9

Howship’s lacunae

Question 10

what are the 2 borders of the osteoclasts during active resorption?

Answer 10

ruffled- facing bone marrow that is folded irregularly

clear zone- site of adhesion b/w cell and bone matrix (sealed)

Question 11

how do osteoclasts break down bone?

Answer 11

1. secrete collagenase and other enzymes into microenvironment
2. pump protons into the pocket = acidic
3. dissolves Ca+ and digests collagen

Question 12

what controls osteoclast activity?

Answer 12

hormones and cytokines

Question 13

what do calcitonin receptors do to osteoclasts?

Answer 13

when activated, they turn off the osteoclasts in order to lower the calcium level in the blood

Question 14

what does parathyroid hormone do to osteoblasts and osteoclasts?

Answer 14

osteoblasts have a parathyroid receptors
when activated they produce a cytokine (osteoclast activating factor) that stimulated osteoclasts
INCREASES blood Ca+

Question 15

what accounts for 50% of dry bone weight?

Answer 15

calcium and phosphorus (hydroxyapatite crystals + calcium phosphate)

Question 16

what gives bone harness and resistance?

Answer 16

minerals+ collagen fibers

Question 17

what are sharpey’s fibers?

Answer 17

collagen fibers that penetrate bone matrix and bind the periosteum to the bone

Question 18

what are the 2 layers of the periosteum?

Answer 18

outer layer- collagen fibers + fibroblasts

inner layer - osteoprogenitor cells (fibroblast-like)

Question 19

what makes up the endosteum?

Answer 19

a single layer of osteoprogenitor cells

Question 20

what are key features of primary bone?

Answer 20

random deposition of fine collagen fibers, lower mineral content, and higher proportion of osteocytes

Question 21

where can you find primary bone in an adult?

Answer 21

tooth sockets
sutures of the skull
some tendon insertions

Question 22

what is the typical organization of secondary bone?

Answer 22

collagen fibers are in lamellae (‘layers’)
lamellae are parallel and concentric around a vascular canal
the lacunae containing the osteocytes are between the lamellae

Question 23

what are Haversian systems?

Answer 23

concentric lamellae between the inner and outer circumferential lamellae

Question 24

what are interstitial lamellae?

Answer 24

irregularly shaped areas between haversian systems

Question 25

what is the basic organization of the haversian system or osteon?

Answer 25

lamellae are laid down successively from the periphery inward fiber are arranged parallel to each other in a helical course within a lamellae fibers change direction w/ each successive lamellae

Question 26

how do the central canals in the osteons communicate w/ marrow cavities, periosteum, or other canals?

Answer 26

transver or oblique Volkmann's canals (perforate lamellae)

Question 27

what bones are formed by intramembranous ossification?

Answer 27

frontal and parietal bones part of occipital and temporal bones mandible contributes to growth of short bones and thickening of long bones

Question 28

what is the basic process of intramembranous ossification?

Answer 28

1. primary ossification centers form 2. cells differentiate into osteoblasts 3. osteoblasts make matrix that calcifies 4. developing bone forms walls that make cavities 5. ossification centers grow and fuse 6. bone formation dominates over resorption= compact bone

Question 29

what bones undergo endochondral ossification?

Answer 29

short and long bones

Question 30

what are the basic steps of endochondral ossification?

Answer 30

1. starts in a piece of hyaline cartilage 2. bone collar forms through intramembranous ossification 3. the local cartilage undergoes matrix calcification 4. blood vessels penetrate bringing in osteoprogenitor cells 5. osteoblasts begin laying down bone matrix over the primary ossification centers 6. secondary ossification centers appear at the ends (articular and epiphyseal cartilage remains) 7. ossification centers leave cavities that fill w/ bone marrow

Question 31

what are the 5 zones of the epiphyseal cartilage?

Answer 31

``` (superior to inferior) resting zone proliferative zone hypertrophic cartilage zone calcified cartilage zone ossification zone ```

Question 32

what is the resting zone?

Answer 32

hyaline cartilage w/o any changes

Question 33

what is the proliferative zone?

Answer 33

chondrocytes divide rapidly and form columns of stacked cells

Question 34

what is the hypertrophic cartilage zone?

Answer 34

large chondrocytes w/ cytoplasmic glycogen

Question 35

what is the calcified cartilage zone?

Answer 35

the chondrocytes die and the septa become calcified

Question 36

what is the ossification zone?

Answer 36

osteoblasts form and deposit bone matrix | blood and capillaries and osteoprogenitor cells invade

Question 37

what are the two mechanisms of calcium mobilization?

Answer 37

1. hormone action (calcitonin/ parathyroid) | 2. simple ion transfer from hydroxyapatite crystals to the interstitial fluid

Question 38

what are the two layers of synovial joint capsule connective tissue?

Answer 38

``` fibrous layer (external) synovial layer (internal) ```

Question 39

synovial fluid has a high concentration of what in it?

Answer 39

hyaluronic acid