21: Bones

Question 1

components of bone matrix

Answer 1

osteoid, mineral component, hydroxyapatite

Question 2

osteoid

Answer 2

type I collagen + some GAGs

Question 3

woven vs lamellar bone

Answer 3

1. woven: rapidly produced in fetal development + fx repair -> less integrity
2. lamellar: slowly produced -> strong parallel collagen

Question 4

osteocytes

Answer 4

inactive osteoblasts that control Ca and PO levels

Question 5

what type of cells are osteoclasts

Answer 5

multi-nucleated macrophages

Question 6

type of ossification used to produce long bones vs flat bones

Answer 6

1. long bones: endochondral ossification

2. flat bones: intramembranous ossification

Question 7

RANK and RANKL

Answer 7

1. RANK: receptor on osteoclast precursors

2. RANKL: on osteoblasts

Question 8

OPG

Answer 8

osteoprotegerin - a decoy made by osteoblasts that blocks RANKL binding to RANK -> less osteoclastic breakdown

Question 9

three hormones/products that help build bone + three that help destroy it

Answer 9

1. build bone: estrogen, testosterone, vit D

2. destroy: PTH, IL-1, glucocorticoids

Question 10

M-CSF in bone

Answer 10

osteoclast precursors have an M-CSF receptor that stimulates osteoclast production

Question 11

collagen type in bone vs cartilage

Answer 11

1. bone: Type I

2. cartilage: Type II

Question 12

dystosis vs dysplasia of bone

Answer 12

1. dystosis: local disruption of migration/condensation of mesenchyme and differentiation into cartilage
2. dysplasia: global disorganization of bone/cartilage

Question 13

gene involved in brachydactyly

Answer 13

HOXD13

Question 14

gene in cleidocranial dysplasia

Answer 14

RUNX2

Question 15

cleidocranial dysplasia

Answer 15

AD condition with patent fontanelles, delayed cranial suture closure, and wormian bones (extra bones within cranial sutures)

Question 16

MC inherited disorder of CT

Answer 16

osteogenesis imperfecta

Question 17

three types of fractures seen in both osteogenesis imperfecta and child abuse

Answer 17

1. fx in multiple stages of healing
2. rib fx
3. spiral fx

Question 18

maximal skeletal mass peak

Answer 18

happens around young adulthood, peak is affected by hereditary factors, physical activity, diet, and hormones

Question 19

normal age-related loss of bone mass per year

Answer 19

0.7%

Question 20

compound fracture

Answer 20

bone communicates with skin surface

Question 21

comminuted fracture

Answer 21

bone is fragmented

Question 22

stress fracture

Answer 22

slowly developing fracture that follows a period of increased physical activity

Question 23

greenstick fracture

Answer 23

extending partially thru bone (common when infants have soft bones)

Question 24

pathologic fracture

Answer 24

occurs when bone is weakened by underlying disease

Question 25

first four steps in fracture healing

Answer 25

1. blood vessel rupture -> hematoma
2. clotted blood forms a fibrin mesh seal
3. degranulated platelets release PDGF, TGF-B, and FGF to activate osteoprogenitors -> osteoclast and osteoblast activation
4. end of 1st week: soft tissue callus (procallus)

Question 26

osteomyelitis

Answer 26

inflammation of the bone and marrow, almost always following infection

Question 27

major pathway of pyogenic osteomyelitis in kids

Answer 27

heme spread from trivial mucosal injuries (chewing hard foods, defecation)

Question 28

MC tumor in bones

Answer 28

metastases

Question 29

three MC primary bone tumors

Answer 29

osteosarcoma, chondrosarcoma, Ewing’s sarcoma

Question 30

MC primary malignant tumor of bone

Answer 30

osteosarcoma

Question 31

MC benign bone tumor

Answer 31

osteochondroma