Bone Development And Growth

Question 1

Intramembranous Ossification

Answer 1

. Process used in formation of most flat bones

. Occurs in layer (membrane) of fetal mesenchymal tissue

Question 2

Intramembranous ossification steps

Answer 2

. Mesenchymal cells (plueripotential) develop into osteoblasts once they secrete osteoid
. Blasts entrap themselves in matrix so cell become osteocytes
. Osteoid mineralized to form mature bone matrix

Question 3

Where does intramembranous ossification have a tendency to occur?

Answer 3

. Ossification centers w/in mesenchymal membrane initially forming immature bone
. Greater bone formation on surfaces of developing bone forming inner and outer plates of compact bone separated by diploe

Question 4

Endochondral bone formation

Answer 4

. Process of bone formation where bone is laid down on pre-existing cartilage model

Question 5

Where does cartilage model arise from in endochondral ossification?

Answer 5

. Arises from mesenchyme

Question 6

When does endochondral ossification process start?

Answer 6

. When bone collar appears
. Surrounds diaphysis of cartilage model and is produced by osteoblasts that emerge w/in fetal perichondrium so it becomes fetal periosteum

Question 7

Endochondral ossification steps

Answer 7

. Bone collar forms
. Cartilage adjacent to cartilage calcifies forming calcified cartilage matrix and blood vessels penetrate bone collar to bring osteoprogenitor cells to central region
. Osteoprogenitor cells adhere to calcified matrix remnants and differentiate into osteoblasts
. Osteoblasts lay doesn’t osteoid

Question 8

Primary ossification center

Answer 8

Initial site of bone deposition

Question 9

Secondary ossification centers

Answer 9

. Develop in epiphyses of long bones

. only cartilage that remains with these is articular cartilage and the epiphyseal growth plate

Question 10

Resting zone

Answer 10

Normal looking hyaline cartilage

Question 11

Proliferative zone

Answer 11

Chondrocytes quickly divide and form columns of cells parallel to long axis of bone

Question 12

Hypertrophic cartilage zone

Answer 12

Chondrocytes stop to proliferate,,, enlarge, and become principal engine of bone growth

Question 13

Hypertrophic chondrocytes

Answer 13

Direct mineralization of surrounding matrix, attract blood vessels, and promote transformation of adjacent perichondral cells to become osteoblasts

Question 14

What proteins are produced by hypertrophic cartilage and what do proteins do

Answer 14

. Type X collagen (assoc. w/ mineralization of cartilage matrix)
. Vascular endothelial growth factor (VEGF): stimulates blood vessel growth

Question 15

Zone of calcified cartilage

Answer 15

Cartilage calcifies, hypertrophic chondrocytes die via apoptosis

Question 16

Ossification zone

Answer 16

Empty lacunae invaded by vessels from bone marrow

. Osteoblasts reside in remaining calcified cartilage matrix trabeculae and lay down osteoid

Question 17

Metaphysis

Answer 17

Area immediately below growth plate

Question 18

Interstitial growth of cartilage

Answer 18

. New growth of cartilage produced by epiphyseal plate of long bones in childhood
. Allows bone to grow further

Question 19

Result of cartilage proliferation and bone deposition being even

Answer 19

Epiphyseal plate width is relatively constant until it ossified completely during puberty

Question 20

What age to epiphyseal plates ossify?

Answer 20

20 years old

Question 21

T/F Bone can continue to growth length wise after epiphyseal plate ossifies

Answer 21

F< only can grow width-wise (appositional growth)

Question 22

What is responsible for appositional growth?

Answer 22

Periosteum

Question 23

Rate of bone modeling in children vs. adults

Answer 23

200 times the rate in kids as adults

Question 24

Factors that cause remodeling

Answer 24

. Growth factors
. Pregnancy
. Hormones
. Bone stress from muscular contraction and body movement
. Growth of brain

Question 25

Basis of orthodontics

Answer 25

Ability for bone to remodel under stress

Question 26

Bone fracture steps

Answer 26

. Ruptured blood vessels form hematoma at fracture site
. Damage to matrix from disrupted blood supply causes osteocytes death
. Phagocytic cells remove color and damaged bone

Question 27

How bone fracture is repaired

Answer 27

. Phagocytes remove bone and clot
. Fibroblasts and blood vessels grow into hematoma, form granulation tissue
. Granulation tissue becomes callous
. Periosteum and endosteum produce osteoprogenitors
. Callus stimulates new bone growth
. Callus untied bone ends and with support they heal
. Undergoes remodeling until repaired bone approximates appearance of bone prior to fracture

Question 28

External callus and role in fracture repair

Answer 28

. Callus around fracture
. Thickens causing lack of blood to deeper part of external callus promoting cartilage formation
. Cartilage replaced by bone in similar process as endochondral ossification

Question 29

Internal callus and role in fracture repair

Answer 29

. Between fractured ends and bone
. Osteorogenitor cells invade it and produce trabeculae of primary bone that untied ends of fracture
. Provides support to unit ends of bone

Question 30

Result of inadequate support of bone during healing process

Answer 30

. Abnormal bone structure development