Bone Tissue - Downing

Question 1

What are the 2 steps of bone formation by osteoblasts?

Answer 1

Synthesis of organix matrix (osteoid)

Deposition of inorganix components

Question 2

Where do you find osteoblassts?

Answer 2

They are located on bone surfaces (have an epitheliod appearance

Question 3

What cells form osteocytes?

Answer 3

Osteoblasts that end up getting trapped in the bony matrix

Question 4

How is osteoclast activity regulated?

Answer 4

Osteoblasts have surface receptors for parathyroid hormone (PTH)

Osteoblasts bind PTH
Release ‘osteoclast stimulating factor’
This stimulates osteoclasts to break down bone

Question 5

How do osteocytes communicate?

Answer 5

They have processes that extend out and communicate through gap junctions

(Think prisoners in solitary confinement that communicate through passing notes through hole in the wall)

Question 6

What are canaliculi?

Answer 6

The small passages through the bony matrix that the osteocyte processes travel to communicate, and through which the nutrients and waste materials can travel.

Question 7

Function of the ruffled border of the osteoclast?

Answer 7

The part of the osteoclast that sticks to the bony surface
REMOVE ORGANIC AND INORGANIC PARTS OF THE BONE

INORGANIC
Membranes pump H+ into sub-osteoclastic compartment
-lowers pH and mineral is liberated
-Minerals enter osteoclast and are then delivered to nearby capillaries

ORGANIC

• Osteoclast secretes lysosomal hydrolases, collagenase, and gelatinase into sub-osteoclastic compartment
• Degrade organic components of decalcified bone matrix
• Degradation products are endocytosed by osteoclast
• Broken down into amino acids, monosaccharides, and disaccharides and released into capillaries

Question 8

What is the region of resorbed bony matrix containing an osteoclast called?

Answer 8

Howship’s lacunae

Question 9

What is the important part of the inorganic portion of bone?

Answer 9

*Calcium*
Calcium phosphate
Hydroxyapatite crystals
-Hydrophilic
-Facilitate exchange between crystals and body fluids

Question 10

What are 3 glyoproteins are

colelctveily capable of binding together the cell and matrix components of bone?

Answer 10

Osteocalcin
Osteopontin
Osteonectin

Question 11

Compare Cancellous bone with compact bone:

Answer 11

Cancellous (spongy bone)

• Spicules or trabeculae of bone united to form a network
• Found in interior of bone

Compact (dense bone)

• Found on bone exteriors
• Dense, thick layers

Question 12

Compare Primary vs Secondary bone:

Answer 12

Primary bone
-First bone tissue to appear during growth & repair
“Woven bone”
-Irregular array of collagen fibers

Secondary bone

• Replaces primary bone
• Parallel arrays of collagen
• Lamellar deposition of matrix
• Production of Haversian systems

Question 13

What are the two layers of periosteum?

Answer 13

Fibrous (outer) layer

• Fibroblasts; collagen; elastin
• Protection of bone
• Connection for ligaments

Osteogenic (inner) layer

• Osteoblasts adjacent to bone surface
• Osteoprogenitor cells - precursors to osteoblasts
• Osteoclasts if remodeling is occurring

Question 14

What are Sharpey’s fibers for?

Answer 14

anchor the periosteum to bone!

Question 15

What are heversian and volkmann’s canals?

Answer 15

Haversian canals run parallell with the bone tissue

Volkmann’s canals run perpendicular (or radially) to connect haversian canals and bring arterial connections into the bone

Question 16

Both types of ossification processes (Intramembranous bone formation and
Endochondral bone formation) result in compact and cancellous bone tissue being formed. What are the important differences though?

Answer 16

Intramembranous Ossification

• Embryonic connective tissue precursor
• Connective tissue is well vascularized
• Gives rise to ‘membrane’ bones
• *Bones of skull; mandible; maxilla; clavicles

Endochondral Ossification

• Hyaline cartilage precursor/template
• Cartilage is avascular
• Calcified cartilage matrix removed
• Examples: long bones of body

Question 17

List from distal to proximal in reference to the middle of the long bone, the layers of the epiphysis:

Answer 17

The resting zone
The proliferative zone (looks like pancake stack)
Zone of hypertrophy (cells look swollen)
Zone of calcification (darkening area in histology)
Zone of ossification (merges into the zone of calcification

Question 18

Give me an example of stress-induced remodeling in bone!

Answer 18

Braces!

Question 19

How can disuse adversely affect the bones?

Answer 19

weakening of the bones

Question 20

How can hormonal changes affect bone plasticity?

Answer 20

PTH
Osteoblast has PTH receptors
Osteoblasts then secrete osteoclast-stimualting factor
rate of bone resorption increases

Question 21

What hromrone rpomotes calcium deposition by inhibiting osteoclast activity and increasing matrix deposition of Ca?

Answer 21

Calcitonin

Question 22

What disorder did children get when working long hours in factories with no natural light? and why?

Answer 22

Rickets
Vit D deficiency

• Leads to improper absorption of calcium from the intestinal mucosa and hence individuals have a calcium deficiency
• Incomplete bone matrix calcification
• Spicules distort under strain –> bone deformation

Question 23

Osteomalacia is what?

Answer 23

Sometimes called adult rickets

Prolonged deficiency of vitamin D
Calcium deficiency in adults
Deficient calcification of new bone
Decalcification of existing bone
No bone distortion

Question 24

What is osteoporosis?

Answer 24

Most common in post-menopausal women

Bone tissue diminished
More rapid destruction of bone tissue by osteoclasts than osteoblast formation of bone
1 out of 40 men will suffer an osteoporotic fracture
1 out of 2 women will suffer an osteoporotic fracture
Estrogen therapy helps alleviate this tendency

Question 25

Which cells secrete synovial fluid? What does this fluid do for the synovial joint?

Answer 25

Fibroblasts = type B cells

Synovial fluid

• Lubricates joint
• Provides nutrients for articular cartilages