CTO Quiz 2: Bone Formation

Question 1

Osteogenesis

Answer 1

bone formation
occurs in embryo to form bony skeleton
occurs during adolescence
occurs during adulthood for remodeling and repair

Question 2

Intramembranous Ossification (definition/general)

Answer 2

bone is formed directly from clusters of mesenchymal cells
first produced in trabecular network
flat (ex skull) and some irregular bones
**mechanism of ossification in periosteum and endosteum
fractures heal by this method

Question 3

Endochondral Ossification (definition/general)

Answer 3

initial hyaline cartilage model
bone is deposited on pre existing cartilage matrix
first produced in trabecular network
method used to form long (humerus), short (hand) and some irregular (vertebrae) bones

Question 4

Intramembranous Ossification (process)

Answer 4

starts with condensation of mysenchyme–>differentiation of mesenchymal cells into osteoprogenitor cells–> become osteoblasts–> secrete bone matrix around themselves–>formation of irregular immature primary bone–>becomes nidus for aggregation
osteoblasts aggregate to add layers to the original spicules of bone–>join together initial bone
become osteocytes trapped in developing bone- connected by canaliculi that extend from lacunae to surface of the bone for nurishment
after initial bone formation- bone modeling occurs to convert immature bone to mature
spongy bone- trabeculae become occupied with hematopoietic tissue

Question 5

Compaction

Answer 5

in compact bone intramembranous and endochondral ossification- trabeculae thicken until interveneing spaces are obliterated

Question 6

Fontanelles

Answer 6

gaps between flat bones that don’t meet (skull)

Question 7

Endochondral Ossification (process)

Answer 7

1) formation of cartilage model (chondroblasts–>chondrocytes etc)
2) growth of cartilage model (appositional or interstitial growth)
3) formation of bone collar- perichondrial cells–>osteoblasts–>compact bone just beneath periostium
4) chondrocytes hypertrophy (lack of nutrition)
5) hypertrophic cells secrete type X collagen, alkaline phosphatase and VEGF (promotes blood vessel formation)- promote calcification of cartilage matrix and vascular invasion
6) death of chondrocytes and disintegration of matrix by matrix metalloproteases)
7) ingrowth of blood vessels and osteoprogenitor cells from periosteum first at shaft then at epiphyses
8) Osteoprogenitor cells–> osteoblasts that secrete osteoid- first around areas of calcified cartilage
9) formation of secondary ossification centers (@epiphyseal plates)

Question 8

Epiphyseal Growth Plate

Answer 8

cartilage plate that separates epiphysis and secondary growth centers from shaft
only place where long bones can growh
as grow, less and less cartilage in plate- eventually becomes all ossified- bone will not increase in length, leaves behind epiphyseal line
both interstitial (length) and apposeal (width) growth

Question 9

Where does cartilage remain after endochondral ossification?

Answer 9

articular surfaces and epiphyseal plate

Question 10

Bone Growth (Length)

Answer 10

a long bone can only increase in length at the epiphyseal plate
proliferation of cartilage occurs on epiphyseal side of the plate, while bone growth occurs on diaphyseal side
activity of epiphyseal plate stimulated by growth hormone

Question 11

5 Zones of Epiphyseal Growth Plate

Answer 11

cartilage above
1) resting zone- hyaline cartilage
2) zone of proliferation- chondrocytes divide rapidly and form columns of cells
3) zone of hypertrophy- cells hypertrophy- secrete compounds
4) zone of calcification- matrix becomes calcified, cells die
5) zone of ossification- blood vessels invade bringin osteoprogenitor cells; osteoblasts deposit bone matrix on calcified matrix
bone formed below

Question 12

Bone Growth (Width)

Answer 12

thicken bone
bone established beneath periosteum by appositional growth
at same time bone is resorbed from inner aspect of shaft
–>increases diameter AND marrow cavity

Question 13

Bone Remodeling

Answer 13

bones are reshaped during osteogenesis (primary–>secondary), growth, repair and in response to forces applied to them
involves osteoblast and osteoclast activity
activity of cell types changes as people age
growing bone- bone deposition > bone resorption
adulthood- bone deposition = bone resorption
osteoporosis- bone resorption > bone depostion

Question 14

Calcium Regulation

Answer 14

bone is major store of Ca in body
affected by hormonal regulation
can break down bone to increase blood Ca or build up bone to decrease blood Ca
can have additional effects on body

Question 15

Calcitonin

Answer 15

released by cells in thyroid in response to high serum calcium
stimulates activity of osteoblasts
decreases activity of osteoclasts
results in production of bone and reduced Ca in serum

Question 16

PTH

Answer 16

released by parathyroid glad in response to high serum Ca
activates osteoclasts
results in bone breakdown and increased Ca in serum

Question 17

Hypertrophic Cell Secretion

Answer 17

type X, alkaline phosphatase, VegF (vascular endothelial growth factor)