Histology: Bone Structure

Question 1

How are bones classified?

Answer 1

according to shape

Question 2

What is the structure of long bones?

Answer 2

• tubular in shape
• consist of 2 ends
  a) proximal end
  b) distal end
• consist of 1 long shaft
  a) diaphysis

Question 3

What is metaphysis?

Answer 3

The junction between the diaphysis and the epiphysis.
(between the bones center and beginning/end)

Question 4

What structure covers the bone?

Answer 4

the periosteum

Question 5

What is the periosteum?

Answer 5

A connective tissue membrane that attaches to the outer surface of bones.

Question 6

What are bone cavities lined by?

Answer 6

endosteum

Question 7

What is the endosteum?

Answer 7

A single layer of cells that contains osteoprogenitor (endosteal) cells.

Question 8

What layers does the periosteum consist of?

Answer 8

1) the outer fibrous layer
2) the inner cellular layer

Question 9

Describe the structure of the outer fibrous layer of the periosteum.

Answer 9

• irregular
• dense connective tissue type
• high percentage of collagenous matrix & small percentage of cells
• divides into 2 layers: the superficial and deep layer.

Question 10

What two layers does the periosteum (outer fibrous layer) divide into?

Answer 10

1) the superficial layer
2) the deep layer

Question 11

How does the superficial and deep layer of the periosteum compare?

Answer 11

the superficial layer is more VASCULAR and receives PERIOSTEAL VESSELS.

the inner layer is a fibro-elastic layer.

Question 12

What does the deep layer of the periosteum consist of?

Answer 12

the fibrio-elastic layer

Question 13

What is the inner cellular layer of the periosteum made up of?

Answer 13

osteoprogenitor cells

Question 14

What is another name used for the inner cellular layer?

Answer 14

the osteogenetic layer

Question 15

What does the inner layer contain? (osteo-) Where?

Answer 15

osteoblasts in young developing bones

Question 16

Are osteoblasts in adult bones present or absent?

Answer 16

• can be absent
• appear whenever required (eg. fracture healing)

Question 17

What are osteoprogenitor cells?

Answer 17

• multipotent stem cells
• undergo mitosis divisions
• differentiate into osteoblasts

Question 18

What is the endosteum? How is it identified?

Answer 18

• a membrane lining the inner surface of the bony wall
• identified as the lining membrane of the bone marrow cavity

Question 19

What does the endosteum line?

Answer 19

• the Haversian canal
• all the internal bone cavities

Question 20

What does the endosteum consist of?

Answer 20

• a layer of flattened osteoprogenitor cells
• type III collagenous fibers (reticular fibers)

Question 21

What is thinner, the endosteum or the periosteum?

Answer 21

The endosteum is noticeably thinner.

Question 22

What is an immature (woven) bone?

Answer 22

bone tissue formed during development

Question 23

What is bone tissue called which is formed during development?

Answer 23

immature (woven) bone

Question 24

How does immature (woven) bone differ from mature (lamellar) bone?

Answer 24

collagen fiber arrangement.

Question 25

How is bone tissue classified?

Answer 25

1) compact 2) spongy

Question 26

Where is compact bone located?

Answer 26

outside and beneath the periosteum.

Question 27

What forms internal spongy bone?

Answer 27

a meshwork of trabeculae

Question 28

What is the development of bones classified as?

Answer 28

1) ENDOCHONDRAL (a cartilage model serving as the precursor of the bone) 2) INTRAMEMBRANOUS OSSIFICATION (without the involvement of a cartilage presursor)

Question 29

What is endochondral development?

Answer 29

a cartilage model serving as the precursor of the bone.

Question 30

What is intramembranous ossification?

Answer 30

a cartilage precursor is not involved.

Question 31

What bones develop by intramembranous ossification?

Answer 31

- flat bones of the skull - mandible (lower czaszka) - clavicle (obojczyk)

Question 32

What bones develop by endochondral ossification.

Answer 32

all bones except: - mandible - clavicle - flat bones of the skull

Question 33

What does hyaline cartilage undergo in early fetal development?

Answer 33

the process of endochondral ossification.

Question 34

What is hyaline cartilage in the process of endochondral ossification?

Answer 34

the precursor of bones

Question 35

What happens during the development process? What happens to hyaline cartilage?

Answer 35

most of the hyaline cartilage is replaced by bones. residual cartilage at the proximal and distal ends of the bone served as growth sites (EPIPHYSEAL GROWTH).

Question 36

What is EPIPHYSEAL GROWTH?

Answer 36

residual cartilage at the proximal and distal ends of the bone served as growth sites.

Question 37

When does the cartilage at the proximal and distal ends of the bone remain functional (epiphyseal growth)?

Answer 37

as long as the bone is growing in length.

Question 38

What is the model formed in endochondral ossification?

Answer 38

the hyaline cartilage model

Question 39

What do osteoprogenitor cells surrounding the hyaline cartilage model differentiate into?

Answer 39

1) bone-forming cells that initially deposit bone onto the cartilage surface (periosteal BONY COLLAR) 2) penetrate the diaphysis (to form the PRIMARY OSSIFICATION CENTER)

Question 40

What is "periosteal BONY COLLAR"?

Answer 40

bone forming cells that deposit bone in the cartilage surface

Question 41

How is the primary ossification center formed?

Answer 41

bone forming cells penetrate the diaphysis.

Question 42

How is the secondary ossification center developed?

Answer 42

within the epiphyses.

Question 43

What separates the primary and secondary ossification centers?

Answer 43

the epiphyseal growth plate

Question 44

What does the epiphyseal growth plate do?

Answer 44

it provides a source for new cartilage involved in bone growth (children and adolescents).

Question 45

Does the epiphyseal growth plate have several zones?

Answer 45

yes, eg. - reserve cartilage - zone of proliferation - zone of hypertrophy - zone of calcified cartilage - zone of resorption

Question 46

What happens during intramembranous ossification?

Answer 46

bone formation is initiated by condensation of mesenchymal cells that differentiate into osteoblasts.

Question 47

How are ossification centers formed?

Answer 47

some spindle shaped, pale staining mesenchymal cells migrate and aggregate in specific areas (eg. the region of flat bone development in the head)

Question 48

What initiates the process of intramembranous ossification?

Answer 48

condensation of cells within the mesenchymal tissue

Question 49

What do mesenchymal cells in ossification centers elongate and differentiate into?

Answer 49

osteoprogenitor cells

Question 50

What do osteoprogenitor cells further differentiate into?

Answer 50

osteoblasts

Question 51

What do osteoblasts deposit?

Answer 51

unmineralized bone matrix (the osteoid).

Question 52

Where do the osteoblasts accumulate?

Answer 52

at the periphery of the ossification center

Question 53

What do osteoblasts do at the periphery of the ossification center?

Answer 53

continue to secrete osteoid toward the center of the nodule.

Question 54

What happens when the process of ossification continues (after osteoblasts secrete the osteoid towards the center of the nodule). What happens to osteoblasts?

Answer 54

osteoid undergoes mineralization and trapped osteoblasts become osteocytes.