Bone Structure And Physiology

Question 1

Describe bone function: support

Answer 1

Mineralised connective tissue when fully developed-.
 30% organic material 45% inorganic (hydroxyapatite).  Support the body and protect internal organs.
 Bones of legs, pelvis, vertebrae support body, mandible supports teeth. Bones enclose and protect brain, spinal chord, lungs, heart, pelvic visera, bone marrow.
 Allows movement.
 Bones provide attachment for muscles so allowing leverage. (e.g. leg/arm movements, ventilation of the lungs).

Question 2

Describe bone function: metabolic

Answer 2

Haematopoiesis.
 Bone marrow (red marrow) is the major producer of blood cells including cells of the immune system.
 Calcium Homeostasis. (99% body Ca, 85% P04).
 Serum Ca2+ levels maintained by interplay between intestinal absorption, renal excretion and skeletal mobilisation or uptake.

Question 3

Bone types

Answer 3

Cortical/Compact/laminar:
 approx 80% of skeleton, dense, very strong, forms the outer layer of all bones.

/
Cancellous
:
-
Trabecular
 porous meshwork of bone. Makes up approx. 20% of the skeleton, mainly in axial skeleton. Bone strength also determined by the trabecular microstructure-can change in disease e.g. osteoporosis.

-
Woven bone:
 forms quickly during periods of repair or rapid growth and is remodelled into lamellar bone

Question 4

Histology of woven bone

Answer 4

Question 5

Describe the alveolar process

Answer 5

Alveolar process is a thickened ridge which contains the tooth sockets:-supports the teeth

Question 6

Which tooth sockets does the alveolar process contain?

Answer 6

Outer & inner cortical plates
 Trabecular or cancellous bone filling

Question 7

Alveolar bone:- destruction in periodontal disease

Answer 7

Question 8

Titanium implant inserted into alveolar bone

Answer 8

Question 9

Bone types

Answer 9

Trabecular bone
 Cortical bone
 Woven bone (“repair material” formed at repair sites such as fracture callus-remodelled into “mature” bone type over time).

Question 10

The cell-types in bone

Answer 10

Osteoclast (Oc):
 Large multinuceated cells. Bone resorbing cells.
 Osteoblast (Ob):  Bone forming cells.
 Osteocyte:
 Originate from osteoblasts which have become embeded in the bone matrix. Involved in sensing mechanical loads and Ca homeostasis.
 Bone lining cells.
 Originate from osteoblasts. Line quiescent
periosteoal and endosteal surfaces of bone .
 Osteoprogenitor cells (stromal cells).  Precursors of osteoblastic lineage

Question 11

What is the importance of bone remodelling

Answer 11

To carry out its functions bone is constantly being remodelled (i.e. bone is constantly being destroyed and reformed).
 Remodelling estimated to occur at 1-2 million microscopic sites/skeleton at any one time

Question 12

Phases of bone remodelling

Answer 12

Remodelling starts with a resorption phase  bone ECM destroyed and removed. This
phase takes approx 3 weeks/remodelling site.  A bone formation phase then follows.
 New ECM is formed and mineralised-this phase takes 3-4 months/remodelling site

Question 13

Mechanism of bone remodelling step 1 - 4

Answer 13

1. Recruitment of osteoclast precursors to remodeling site
2. Osteoclast precursors mature into osteoclasts.
3. Bone lining cells erode a little ECM and leave
   the remodeling site.
4. Osteoclasts bind to the exposed ECM and digest the bone matrix with enzymes to form resorption pits (Howship’s Lacuna)

Question 14

Mechanism of bone remodelling step 5 - 9

Answer 14

Osteoclasts stop digesting matrix and die (apoptosis).
6. 7. 8. 9.
Osteoblastprecursorsrecruitedtothe remodeling site.
Osteoblast precursors develop into mature osteoblasts.
Osteoblasts make new ECM to fill the resorption pit made by the osteoclasts.
When the synthesis of matrix is complete, the
new bone surface becomes covered in bone
lining cells.

Question 15

What happens to osteoblasts trapped within the ECM

Answer 15

Osteoblasts trapped within the ECM mature into osteocytes