Bones structure and function Flashcards
through which two processes do bones change their structure?
modeling & remodeling
why do bones undergo modeling?
to adapt to changing biomechanical forces
why do bones undergo remodeling?
to remove old, microdamaged bone & replace it with new bone
what are the 4 general categories of bone?
long bone, short bone, flat bone & irregular bone
what are 2 examples of long bones?
tibia & femur
what are 2 examples of short bones?
patella & tarsals
what are 2 examples of flat bones?
ribs & scapulae
what are 2 examples of irregular bones?
vertebrae & coccyx
Name the 6 functions of the skeleton
structural support
permits movement - bones act as levers for muscles
organ protection
maintain mineral homeostasis & acid-base balance
bones act as a reservoir for growth factors and cytokines
environment for haematopoiesis
what type of formation do long bones undergo?
membranous and endochondral
what type of formation do flat bones undergo?
membranous
describe the composition of long bones
diaphysis - hollow shaft of thick cortical bone
trabecular meshwork covered in thin cortical shell above growth plates (rounded epiphyses) and below growth plates (cone-shaped metaphyses)
What are the physical properties of cortical bone?
It is dense and solid and is made up of haversian systems.
What does cortical bone surround?
Marrow space.
What is the haversian system wall made of?
Concentric lamellae.
Which is more metabolically active - cortical bone or trabecular bone?
Trabecular bone.
Name the outer surface of cortical bone and its function.
The periosteal - for growth and fracture repair.
Name the inner surface of cortical bone and its function.
The Endosteal - has higher remodelling activity than periosteal due to more strain and cytokine exposure.
Describe the structure of trabecular bone.
Honeycomb-like network of trabecular plates and rods.
Where is trabecular bone found?
Interspersed in bone marrow.
What structures are made from lamellar patterns?
Cortical and trabecular bone.
What is a lamellar pattern?
Collagen fibrils laid down in alternating patterns.
How is the structure of the Lamella pattern related to its function?
The alternating orientation of collagen fibrils makes the structure extremely strong.
Describe the structure of woven bone.
There is no lamellar pattern. The collagen is disorganised.
Is woven bone strong or weak?
weak
What is woven bone?
The form of primary bone.
What is the periosteum?
The fibrous connective tissues surrounding the cortical exterior.
What is the function of the periosteum?
It contains blood vessels, nerve fibres, osteoblasts and osteoclasts.
What is the endosteum?
The membrane of the inner cortical and trabecular bone and Volkmann canals.
What is the function of the endosteum?
Contains vessels, osteoblasts and osteoclasts.
Name the three ways in which bones change their shape and structure.
Growth modelling and remodelling.
In which two ways can bone growth occur?
The longitudinally and radially.
When does bone growth occur?
During childhood
Describe the process of longitudinal growth.
Cartilage proliferates in epiphyseal and metaphyseal. It becomes mineralized and forms primary new bone. occurs at the growth plates.
What is modelling?
When bones change shape due to physiologic influences or mechanical forces - the gradual adjustment of the skeleton to the forces it encounters.
Why do bones widen with age?
It is the response to periosteal opposition of new bone and endosteal reabsorption of old bone.
What is Wolff’s law?
Long bones change shape to accommodate stress they’re put under
What happens during bone modelling?
Bones widen or change axis by adding and removing parts of the bone via osteoblast and osteoclasts.
What is more frequent in adults - modelling or remodelling?
remodelling.
What is remodelling?
It is the continuous removal of discrete packets of old bone. It is replaced with new proteinaceous matrix, which is then mineralized form bone.
Why is remodelling important?
bone is renewed to maintain strength and mineral homeostasis.
Why is it important that old bonus reabsorbed?
It prevents bone micro damage accumulation.
At what stage in life does remodelling occur?
At all stages, from birth until death.
What does a remodelling unit consist of?
A tightly coupled group of osteoclasts and osteoblasts, which reabsorbed and form bone.
What is the 4 phase cycle of remodelling?
Activation reabsorption reversal and formation.
What is meant by bone balance?
The difference in old bone reabsorption and new bone formation
Describe the bone balance of periosteal.
Mildly positive.
Describe the bone balance of endosteal.
Mildly negative.
Describe the bone balance of trabecular bone.
Mildly negatives.
What is the role of osteoclasts?
Osteoclasts reabsorb bone.
What is the role of osteoblasts?
Osteoblasts synthesise new bone matrix on bone falling surfaces.
What are osteocytes?
Differentiated osteoblasts located in the Lacunae of mineralised bone.
List some of the roles of osteocytes.
Support bone structure and metabolism
support protective lining cells that cover surface of quiescent bone.
Can act as phagocytes.
connexion to each other and bone surfaces
mechanosensation.
Why can osteocytes act as phagocytes?
They contain lysosomes.
What are gap junctions?
Gap junctions link osteocytes metabolically and electrically and are needed for osteocyte maturation activity and survival.
One of the roles of osteocytes is mechanosensation. What is this?
They transduced stress signals from bending and stretching bone to biologic activity to allow bone remodelling.
how does apoptosis of osteocytes occur and what does this affect?
Gap junctions may be disrupted, which leads to less and less remodelling and thus weak bones.
Describe bone composition.
50 to 70% minerals.
20 to 40% organic matrix
5 to 10% water
< 3% lipids.
What is the function of the inorganic matrix in bone?
Provides mechanical rigidity.
It gives load-bearing strength.
Describe mineralization of the inorganic matrix.
Minerals are deposited in hole zones between ends of collagen fibrils .
Describe the composition of organic matrix.
85 to 90% collagen, 10 to 15% non collagenous.
What type of collagens are present in organic matrix?
Type 1 type 3 type 5 and FACIT collagens.
What is the role of FACIT collagens?
They act as molecular bridges to organise and stabilise extracellular matrices.
What non-collagenous substances are present in organic matrix?
Proteoglycans, glycosylated proteins y-carboxylated proteins.
What is the role of non-collagenous substances inorganic matrix?
Serve functions like mineral deposition, regulation and bone cell activity.
