Lecture 8

Question 1

6 key functions of bone

Answer 1

• structure
• locomotion (with muscles)
• organ protection
• blood cell formation
• calcium homeostasis
• fixation of toxic compounds

Question 2

how many bones do we have (at birth and as adults)

Answer 2

Over 270 at birth.
206 as adults (some have fused)

Question 3

2 types of bone in the bone structure

Answer 3

cortical (hard) bone
trabecular (spongy) bone

Question 4

what is the internal structure of cortical bone ? what is the result ?

Answer 4

osteons made of concentric bone lamellae and a central canal -> very strong and resistant

Question 5

bone in evolution : first cells that appeared, which species has bone marrow

Answer 5

osteocytes appeared 400M years ago.
Tetrapods are the only with bone marrow (amphibiens, birds, us, …)

Question 6

what are the 2 components of bone and their % ?

Answer 6

1/3 organic (mostly collagen type I)
2/3 inorganic = hydroxyapatite

Question 7

3 bone cells and their roles, and their cellular origin

Answer 7

1) osteoblasts : bone formation, bone marrow-derived mesenchymal progenitors
2) osteoclasts : bone resorption, giant cell with many nuclei, bone marrow-derived hematopoietic progenitors
3) osteocytes : sense the state of the bone and send signals to the other two cells, derived from osteoblasts

Question 8

how do osteoclasts resorb bone ? explain for collagen and hydroxyapatite

Answer 8

Osteoclast attaches to bone and forms a resorption lacuna with a ruffled border.

1) collagen is digested by enzymes (cathepsin K)
2) low pH in lacuna : acidic environment degrades hydroxyapatite

Question 9

what are the two processes to form bone ? which way to host bone marrow ?

Answer 9

1) intramembranous : direct differentiation of mesenchymal cells into osteoblasts : fibrous tissue -> bone

2) endochondral : mesenchymal -> chondrocytes (cartilage) that secrete factors to attract blood vessels -> provide circulating osetoprogenitor cells -> bone formation

2) happens in growth plates f.ex and is needed to host bone marrow

Question 10

what are the three things an ideal bone substitute would need ?

Answer 10

1) osteoconductive : serve as scaffolding to support growth (strong and porous)

2) osteoinductive : presence of GF (like BMP) which recruit stem cells and induce differentiation into osteoblasts

3) osteogenic : presence of osteoblasts (or mesenchymal stem cells)

Question 11

what is the current surgical standard ? Other available alternatives ?

Answer 11

current = autologous transplant, bone usually taken from hip : osteoconductive and inductive but limited amounts and donor site morbidity

other : devitalized cancellous bone, synthetic materials (small defects), graft infused with BMPs

Question 12

what are the steps performed in tissue engineering ? cell source for bone tissue eng ? 2 sources

Answer 12

biopsy -> cell isolation -> cultivation -> proliferation -> scaffold -> growth factors and mechanical stimuli -> implantation

for bone : adult cells from bone marrow or adipose tissue -> mesenchymal stem cells

Question 13

what was the issue with most bone grafts ? what do we want ?

Answer 13

most of the cases : bone formed by osteoconduction

We want osteogenicity ; bone that forms from the graft itself