Bones 1

Question 1

What are the functions of bones?

Answer 1

Structural

Hearing

Protection (of soft tissue and internal organs)

Standing/support

Mineral storage - main reservoir for calcium and phosphorus

Movement: - Transmit force of muscular contraction, attachment site for muscles

Metabolic -

• Haematopoiesis, blood cell production In bone marrow
• Homeostasis of ionised calcium (Ca2+) in blood
• Defence against acidosis

Question 2

What are the different classes of bones?

Answer 2

Long

Short

Flat

Irregular

Sessamoid

Question 3

What is the name given to the fibrocartilagenous layer that encloses bone?

Answer 3

Periosteum

Question 4

Where is red bone marrow, what does it produce?

Answer 4

Metaphysis - production of red blood cells

(metaphysis is the region between the epiphysis and the diaphysis)

Question 5

What is the function of yellow bone marrow and where is it found?

Answer 5

Yellow bone marrow is found in the diaphysis - mainly contains fat cells

Question 6

What percentage of skeletal mass is cortical bone and spongy bone?

Answer 6

Trabecular bone = 20% bone mass

Cortical bone = 80% skeletal mass

Question 7

What type of bone development forms flat bones?

Answer 7

Intramembranous ossification

Question 8

What is the process of intramembranous ossification?

Answer 8

Bone forms as a fibrous plate

Bone cells differentiate from fibroblasts and haematopoietic precursors

Question 9

How do long bones form?

Answer 9

Endochondral ossification

Question 10

What is the process of endochondral ossification?

Answer 10

Bone forms as cartilage (3 months)

Blood vessels invade cartilage

Osteogenic (bone forming) cells invade with blood vessels

Cartilage remains in growth plate

Growth plate fuses at age 21 in males and 18 in females

Question 11

How is bone composition determined?

Answer 11

Method to determine composition:

–Bone cores from femoral heads weighed in air

–Dehydrated @ 105°C for 24 hours

• Weighed again
• Water content = wet – dry weight

–Ashed @ 600° C for 24 hours

• Weighed again
• Mineral content = ash weight
• Organic content = dry weight – ash weight

Question 12

Example of subchondral femoral head bone composition

Answer 12

Question 13

What material does bone consist of?

Answer 13

•Hydroxyapatite: Ca10(PO4)6(OH)2

Question 14

What quality does mineral add to bone?

Answer 14

Rigidity

Question 15

How does the mineralisation of bone change with time?

Answer 15

•Recently deposited bone has less mineral

–dark gray

–nearer the surface

•Older bone is more mineralized

–light grey/white

–further from surface

Question 16

What type of collagen is found in bone?

Answer 16

Type 1

Question 17

What is the structure of collagen type1?

Answer 17

Triple helix protein

Heterotrimer (two a1 chains and one a2 chain)

They combine to make fibrils

Fibrils combine to make fibers

Incorporate bone mineral

Question 18

look

Answer 18

Question 19

What type of water exists in bones?

Answer 19

Pore water (pores within bone e.g haversian canals)

Bound water (loosely or tightly bound, works well with collagen to provide elasticity)

Question 20

How does the water content in our bones change as we age?

Answer 20

The amount of bound water decreases

The amount of pore water increases

Question 21

Which portion of bone sunstance is respoonsible for elasticity?

Answer 21

Organic

Question 22

How is the composition of bone investigated?

Answer 22

Spectroscopy

Question 23

What type of cells are osteoclasts?

Answer 23

– Multinucleated cells formed by the fusion of mononuclear precursors; responsible for degradation of bone

Question 24

WHat is the role of osteoblasts?

Answer 24

Responsible for the synthesis of new bone

Question 25

What are osteocytes?

Answer 25

Osteoblasts that have become embedded within bone, function as sensors of mechanical load

Question 26

How long does it take osteoid to calcify?

Answer 26

About 10 days

Question 27

What organelles are prevalent in osteoblasts?

Answer 27

Endoplasmic reticulum and golgi apparaturs, due to their biosynthetic function

Question 28

How may nuclei are typically found in osteoclasts?

Answer 28

5

Question 29

Where are osteoclasts found?

Answer 29

In pits on the bone surface called resportion bays

Question 30

What gives the osteoclasts cytoplasms’ foamy appearance?

Answer 30

High concentration of vesicles and vacuoles

Question 31

What is the morphologic characteristic of an osteoblast actively resorbing bone?

Answer 31

A ruffled border

Question 32

What is the purpose of the ruffled border?

Answer 32

Increases surface area - thereby increasing the rate of secretion and absorption

Question 33

How do osteoclasts resorb bone?

Answer 33

The osteoclast releases hydrogen ions through the action of carbonic anhydrase (H2O + CO2 → HCO3− + H+) through the ruffled border into the resorptive cavity, acidifying and aiding dissolution of the mineralized bone matrix into Ca2+, H3PO4, H2CO3, water and other substances. Hydrogen ions are pumped against a high concentration gradient by proton pumps, specifically a unique vacuolar-ATPase. This enzyme has been targeted in the prevention of osteoporosis. In addition, several hydrolytic enzymes, such as members of the cathepsin and matrix metalloprotease (MMP) groups, are released to digest the organic components of the matrix. These enzymes are released into the compartment by lysosomes. Of these hydrolytic enzymes, cathepsin K is of most importance.

Question 34

What are the stages of the bone remodelling cycle?

Answer 34

1. Quiescence (inactivity / dormancy)
2. Resorption (osteoblasts stop resorbing bone, osteoblasts are recruited)
3. Reversal
4. Formation - synthesis of new bone matrix

Question 35

How long does the bone remodelling cycle take?

Answer 35

3 months

Question 36

Look

Answer 36

Question 37

How do the headings:

1. Bone mass
2. Mineral
3. Organic

Change with Osteoporosis and Osteoarthritis

Answer 37