Histology - Bone

Question 1

ECM secreted by ____ ?

Answer 1

Osteoblasts, ECM consists of organic/osteoid (90% type I collagen) and ground substance

Inorganic ECM - hyroxyapatite (calcium phosphate)

Also osteocytes (although less metabolically active)

Question 2

Osteogenesis imperfecta

Answer 2

Osteoblast synthesize defective collagen I, forms weak bones

Question 3

Osteomalacia

Answer 3

Weak bones due to calcium deficiency

Question 4

Types of bone formation

Answer 4

Intramembranous ossification (flat bones) vs. endhochondral ossification (long bones)

Question 5

Intramembranous ossification

Answer 5

1. Mesenchymal aggregate where bone will form
2. Differentiate into osteoprogenitos and osteoblasts - osteoblast secrete osteoid (non-mineralized ECM)
3. Osteoid becomes mineralized and embed osteoblasts, becoming osteocytes
4. Once tissue becomes vascularized, blood brings osteoclasts

Question 6

Answer 6

Immature woven bone

Bony spicules merge to form trabeculae

Question 7

How do osteoblasts initiate mineralization of ECM?

Answer 7

By secreting alkaline phosphatase

Question 8

Growth of osteocytes

Answer 8

Appositional growth only (no interstitial growth), this is due to the density of the matrix

Question 9

How do active osteocytes communicate?

Answer 9

Through gap junctions in canaliculi

Question 10

How are osteoclasts formed?

Answer 10

By fusion of monocytes

Osteoclasts resorbs bone and mineralized cartilage

Question 11

Osteoclast activity

Answer 11

Release hydrolytic enzymes that digests matrix. Osteoclasts secrete HCl to decalcify matrix

Question 12

Answer 12

Circle - lacunae

Arrow - lamella

Star - Haversian canal

Lamella circumscribe Haversian canals

Question 13

What is responsible for the tensile and compression strength of bone?

Answer 13

The ECM

Tensile - organic ECM (collagen I)

Compression - Inorganic ECM (Hydroxyapatite, citrate, carbonate, flouride, and magnesium salts)

Question 14

Diaphysis

Answer 14

Shaft of long bone - compact bone

Question 15

Epiphyses

Answer 15

Expanded ends of long bones - spongy bone with hyaline cartilage on articular surfaces

Question 16

Answer 16

Interstitial lamellae - results from remodeling

Question 17

Structural unit of bone

Answer 17

The osteon

Question 18

Answer 18

Left - immature (bundle) bone

Right - mature bone

Question 19

What canals run paralell with the long axis of a bone?

Answer 19

Haversian canals

Question 20

What cells secrete bone ECM?

Answer 20

Osteoblasts and osteocytes

Question 21

What cells are located at the peri/endosteum?

Answer 21

Osteoblasts

Periosteum - periosteal cells

Endosteum - Endosteal cells

Both are osteablast lineage

Question 22

Secondary ossification centers

Answer 22

Become the growth (epiphyseal) plates

Question 23

Remnant of osteon

Answer 23

Interstitial lamellae

Evidence of bone remodeling