Bone Histology

Question 1

What is the cement line?

Answer 1

separates osteon from interstitial lamellae

Question 2

Where is red marrow found in an infant?

Answer 2

everywhere

Question 3

What is in the outer layer of periosteum?

Answer 3

blood vessels and nerves
fibroblasts
collagen fibers
sharpey’s fibers

Question 4

What are osteoblasts?

Answer 4

epithelial-like cells w/ cuboidal/columnar shapes
form matrix of bone tissue
deposit osteoid and control mineralization
give strong cytochemical rxn for alkphos

Question 5

Where are Osteoclasts found?

Answer 5

Howship’s Lacuna

Question 6

What is osteomalacia?

Answer 6

adult form of rickets - progressive softening and bending of bone
vit d deficiency or GI disease

Question 7

How much of bone matrix is organic (not minerals)?

Answer 7

35%

Question 8

What percentage of inorganic bone makes up the matrix?

What is in it?

Answer 8

65%

calcium phosphate, hydroxyapatite

Question 9

What is compact bone?

Answer 9

outer solid cortex surrounding spongy bone

lamellar bone

Question 10

What are osteoprogenitor cells?

Answer 10

mesenchymal origin w/ stem cell properties
found in inner layer of periosteum and endosteum
give rise to osteoblasts
reactivated in times of bone repair

Question 11

What would you find at the center of an osteon?

Answer 11

a haversian canal that houses capillaries and post-capillary venules

Question 12

What are the 2 layers of the periosteum?

Answer 12

inner layer

outer layer

Question 13

What are canaliculi?

Answer 13

tiny little channels in an osteon that allow osteocytes to have projections to connect to other osteocytes and get nutrients

Question 14

What is in the inner layer of the periosteum?

Answer 14

osteoprogenitor cells

osteogenic layer

Question 15

What are inner circumferential lamellae?

Answer 15

internal surface of bone

subjacent to endosteum

Question 16

What is spongy bone?

Answer 16

also known as trabecular/cancellous bone
inner layer
spaces for bone marrow
lamellar or woven

Question 17

What happens to Alkaline Phosphatase when osteoblasts become osteocytes?

Answer 17

alkphos disappears

Question 18

What is rickets?

Answer 18

calcium or vit D defficiency –> defect in mineralization of cartilage in growth plate –> bowed limbs, delayed closure of fontanelles

Question 19

What type of collagen is predominant in bone?

Answer 19

type I

Question 20

Where is red marrow found in an adult?

Answer 20

skull, vertebrae, ribs, clavicle, scapula, pelvis, heads of femur and humerus

Question 21

What is woven bone?

Answer 21

immature/primary
replaced by lamellar
loose arrangement of collagen
more cells, less mineral content
forms during Fx repair/remodeling

Question 22

What is the general composition of bone matrix?

Answer 22

90% ECM and 10% water

Question 23

What are interstitial lamellae?

Answer 23

between osteons

separated from osteon by cement line

Question 24

What is a volkmann’s canal?

Answer 24

transverse vascular channel that connect haversian canals

Question 25

What are sharpey's fibers

Answer 25

found in the outer layer of the periosteum | anchoring collagen fibers penetratint the outer circumferential lamellae

Question 26

What is the outer circumferential lamellae?

Answer 26

external surface of compact bone | under the periosteum

Question 27

Where is the periosteum?

Answer 27

lines bone on the outside

Question 28

What makes up organic bone?

Answer 28

type I collagen osteoid (unmineralized bone) ground substance = proteoglycans, glycoproteins, growth factors/cytokines, Vit K-dep proteins

Question 29

What are osteocytes?

Answer 29

osteoblasts trapped in lacunae in matrix deposit osteoid matrix branches in canaliculi

Question 30

What is osteoporosis?

Answer 30

imbalance btw osteoclast resorption of bone and osteoblast deposition elderly and postmenopausal females

Question 31

What is achondroplasia caused by?

Answer 31

autosomal dominant mutation in FGFR3 --> endochondral growth inhibitted too early --> short limbs

Question 32

What is the function of osteoclasts?

Answer 32

generate a secluded acidic environment for bone resorption mediated by H+-ATPase --> degradation of organic matrix via cathepsin K protease impt in bone remodeling and renewal

Question 33

What is an osteon/ haversian system?

Answer 33

concentrically arranged lamellae around a vascular channel

Question 34

Where is the endosteum?

Answer 34

lines marrow cavity covers spongy walls extends into all cavities of bone contains osteoprogenitor cells

Question 35

What is lamellar bone?

Answer 35

mature/secondary regular parallel arrangement of collagen not visible on H&E stains form of most adult bone = strong, forms slowly

Question 36

How do osteoclasts form?

Answer 36

NOT from osteoblasts | monocytes --> enter bone --> osteoclasts

Question 37

Why do you feel pain if you break a bone?

Answer 37

bc periosteum is innervated by nerves | outer layer

Question 38

What enzyme helps degrade organic bone matrix?

Answer 38

Cathepsin K protease