Bone Formation

Question 1

When does osteogenesis occur?

Answer 1

In embryo to form bony skeleton, during adolescence for growth, during adulthood for remodeling and repair

Question 2

Two processes of bone formation

Answer 2

Intramembranous ossification, endochondral ossification

Question 3

Intramembranous ossification: when does it occur?

Answer 3

used in initial formation of flat bones and some irregular; mech of ossification in periosteum and endosteum; fractures heal through similar process

Question 4

Process of intramembranous ossification

Answer 4

condensation of mesenchyme -> osteoprogenitors -> osteoblasts that secrete bone matrix around themselves -> formation of irregular, immature, primary bone -> aggregation of osteoblasts-> osteoblasts add layers of bone

Question 5

Spicules

Answer 5

islands of developing bone during intramembranous ossification; trabeculae

Question 6

Trabecular network

Answer 6

neighboring spicules contacting one another to form a network during bone development

Question 7

osteoblast

Answer 7

secrete components of bone matrix

Question 8

osteoid

Answer 8

initial non-calcified matrix material secreted by osteoblast

Question 9

osteocalcin

Answer 9

secreted by osteoblasts during intramembranous ossification; bind calcium and alkaline phosphatase

Question 10

osteonectin

Answer 10

binds matrix components to minerals (Ca and phosphate)

Question 11

Endochondral ossification: basic definition

Answer 11

bone deposited on a pre-existing cartilage matrix

Question 12

What bones are formed by endochondral ossification?

Answer 12

short and long bones

Question 13

Fontanelles

Answer 13

flat bones of skull don’t initially meet in a baby

Question 14

Steps of endochondral ossification

Answer 14

(1) formation of cartilage model (2) growth of cartilage model (3) formation of bone collar (4) chondrocyte hypertrophy (5) secretion of materials by hypertrophic cells (6) death of chondrocytes and disintegration of matrix (7) invasion of periosteal blood vessels and osteogenitor cells (8) osteoprogenitor cells develop into osteoblasts that secrete osteoid (9) formation of secondary ossification

Question 15

Bone collar

Answer 15

compact bone just beneath the periosteum that forms during endochondral ossification

Question 16

Where does cartilage remain after endochondral ossification?

Answer 16

articular and epiphyseal

Question 17

What is secreted by hypertrophic cells in endochondral ossification?

Answer 17

type x collagen, alkaline phosphatase (nec for mineral deposition), VEGF (stim vascular invasion)

Question 18

Epiphyseal growth plate zones

Answer 18

resting, proliferation, hypertrophy, calcification, ossification

Question 19

closure of epiphyseal plate

Answer 19

end of growth in length of bone, ossification of epiphyseal plate, occurs at ~20 yrs

Question 20

Length growth in bone

Answer 20

proliferation on epiphyseal side, deposition on diaphyseal side of plate; growth hormones stimulate activity

Question 21

Bone growth: width

Answer 21

new bone established beneath periosteum by appositional growth, bone resorption from inner aspect of shaft –> increased diameter and larger marrow cavity

Question 22

osteoporosis

Answer 22

bone resorption exceeds bone deposition

Question 23

calcitonin

Answer 23

hormone produced by thyroid; decreases osteoclastic activity -> reduced blood Ca++

Question 24

PTH

Answer 24

hormone produced by parathyroid;increases osteoclastic activity -> increased blood Ca++; stims GI tract to absorb Ca++; reduces excretion of Ca++ from kidney

Question 25

explain calcium regulation as it applies to bone metabolism

Answer 25

Question 26

primary ossification center

Answer 26

diaphysis, where endochondrial ossification originates

Question 27

secondary ossification center

Answer 27

form in epiphyses and process is similar to endochondrial ossification in diaphysis (primary ossification centers). Exception: boney collar not formed, cartilage on end of epiphyses –> becomes articular cartilage

Question 28

compaction

Answer 28

process of additional bone being added to fill spaces b/t trabeculae