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Question 1

What is the inorganic phase of bone?

Answer 1

An impure form of hydroxyapatite (Ca10[PO4]6[OH]2).

Question 2

What is the organic phase of bone predominantly composed of?

Answer 2

Type I collagen (~98% by weight).

Question 3

What comprises the cortex of bone?

Answer 3

Compact (cortical) bone.

Question 4

What is contained in the medullary canal of bone?

Answer 4

Variable amounts of cancellous (trabecular) bone fatty and hematopoietic marrow blood vessels and nerves.

Question 5

How is bone tissue categorized histologically?

Answer 5

Into woven and lamellar types based on the organization of type I collagen fibers.

Question 6

What characterizes woven bone?

Answer 6

Collagen fibers arranged in a seemingly haphazard feltwork.

Question 7

What characterizes lamellar bone?

Answer 7

Collagen fibers deposited in parallel arrays either longitudinally or circumferentially.

Question 8

What are the cylindrical units of mature cortical bone called?

Answer 8

Osteons.

Question 9

What does an osteon consist of?

Answer 9

A central Haversian canal surrounded by 4-20 concentric lamellae.

Question 10

What is the outer boundary of each osteon called?

Answer 10

The cement line which includes more noncollagen proteins in addition to mineral and collagen.

Question 11

How do canals communicate within bone?

Answer 11

Through transverse perforating canals (Volkmann canals) that have few

Question 12

How do all cells of an osteon receive nutrients and oxygen?

Answer 12

From vessels in the central canal.

Question 13

What is found between successive lamellae?

Answer 13

Lacunae

Question 14

How do adjacent osteocytes communicate?

Answer 14

Via gap junctions.

Question 15

What are remnants of previous concentric lamellae called?

Answer 15

Interstitial lamellae.

Question 16

What type of bone is trabecular bone?

Answer 16

Lamellar bone

Question 17

Where is trabecular bone principally found?

Answer 17

In the axial skeleton and in the epiphyses and metaphysis of long bones

Question 18

What is the structure of trabecular bone?

Answer 18

A highly porous network of rod- and plate-shaped trabeculae surrounding interconnected pore spaces filled with bone marrow

Question 19

Are trabeculae made of osteons?

Answer 19

No trabeculae are made of lamellar bone but do not contain osteons

Question 20

What is the primary function of osteoblasts?

Answer 20

To produce the organic components of the bone matrix including type I collagen fibers proteoglycans and matricellular glycoproteins

Question 21

How do osteoblasts contribute to bone formation?

Answer 21

They help with the deposition of the inorganic components of bone

Question 22

Where are active osteoblasts located?

Answer 22

Exclusively at the surfaces of the bone matrix bound by integrins

Question 23

What is osteoid?

Answer 23

A layer of unique collagen-rich material produced by osteoblasts between the osteoblast layer and the preexisting bone surface which is not immediately calcified

Question 24

How does osteoid stain compared to mature mineralized matrix?

Answer 24

Osteoid stains lightly compared with the mature mineralized matrix

Question 25

How do osteoblasts communicate with adjacent osteocytes?

Answer 25

Through thin cytoplasmic processes joined by gap junctions

Question 26

What happens to osteoblasts after their synthetic activity is completed?

Answer 26

Some differentiate into osteocytes some become bone lining cells and the majority undergo apoptosis

Question 27

What happens to osteoblasts that become surrounded by the material they secrete?

Answer 27

They differentiate into osteocytes enclosed in lacunae extending long dendritic processes

Question 28

What are the characteristics of osteocytes compared to osteoblasts?

Answer 28

Osteocytes are the most abundant cells in bone but have significantly less rough endoplasmic reticulum (RER) smaller Golgi complexes and more condensed nuclear chromatin than osteoblasts

Question 29

How do osteocytes communicate with each other and with other cells?

Answer 29

Via gap junctions

Question 30

What is the function of osteocytes and what network do they use to carry out this function?

Answer 30

They are mechanosensors and use the extensive lacunar-canalicular network

Question 31

Osteoclasts originate from the fusion of multiple bone marrow-derived monocytes

Question 32

In areas of bone undergoing resorption where do osteoclasts lie?

Answer 32

Within enzymatically etched depressions or cavities in the matrix known as resorption lacunae (Howship lacunae)

Question 33

What is the part of the osteoclast in direct contact with bone called?

Answer 33

The ruffled border

Question 34

What does the membrane domain of osteoclasts form to resorb bone?

Answer 34

A circular sealing zone and surface projections called the ruffled border

Question 35

How do osteoclasts promote bone resorption?

Answer 35

By pumping protons to acidify and promote the dissolution of hydroxyapatite and releasing hydrolytic enzymes for localized digestion of matrix proteins

Question 36

What covers the outside surface of bone?

Answer 36

The periosteum except in areas where bones articulate which are covered by cartilage

Question 37

What is the structure of the periosteum?

Answer 37

An outer fibrous layer resembling dense connective tissue and an inner more cellular layer containing osteoprogenitor cells

Question 38

What are Sharpey’s fibers?

Answer 38

Collagen fibers that extend directly but at an angle into the bone tissue continuous with the collagen fibers of the extracellular matrix of bone

Question 39

What does the endosteum cover?

Answer 39

The marrow cavity and the small trabeculae of bony matrix that project into the marrow cavities

Question 40

What does the endosteum contain?

Answer 40

Osteoprogenitor cells osteoblasts and bone lining cells within a sparse delicate matrix of collagen fibers