Bone Structure Flashcards
What are the four things that make up the skeleton?
- Bone
- Cartilage
- Ligaments
- Tendons
What do ligaments do?
Connect bones to bones
What do tendons do?
Connect muscle to bone
What are the functions of the bone?
- structural support
- protection for soft organs and tissue
- allow movement through tendons
- mineral storage
- source of stem cells (bone marrow)
- source of blood cells
Inside the bone, there is a large amount of what mineral? Why is this mineral important in the bone?
•inside the bone there is a large amount of calcium, this is very important for both function of the bone and the nervous system
How is the level of calcium dissolved into the blood controlled?
The bone has calcium regulators that allow calcium to be dissolved into the bone
Bone is a complex composite material, made up of what two things? At what percentage each?
- inorganic - 65-70wt%dry
* organic - 30-35wt%dry
What is the inorganic bone made of?
- 90% hydroxyapatite (calcium phosphate)
* 10% may be calcium carbonate etc
What is the organic part of the bone made of?
85-90% collagen
Other proteins and cells
What are the four ways bones can be classified by shape?
- long
- short
- flat
- irregular
What makes a ‘long’ bone?
The ratio between length and width is high
What classifies a ‘short’ bone?
Ratio between length and width is the same
What makes a ‘flat’ bone?
Thin bones, only slightly curved
Where can ‘long’ bones be found?
Arms, legs
Where can ‘short’ bones be found?
Wrist, ankle, knee
Where can ‘flat’ bones be found?
Skull, ribs
Where can ‘irregular’ bones be found?
Vertebrae, facial
What are the two ways bones can be specified by structure?
- compact
- spongy
What is the other name for compact bone?
Cortical
What are the other names for spongy bone?
Trabecular, cancellous
What is the typical structure of a long bone?
- Spongy at the top, with lots or pores.
- Compact bone at the centre, more dense than the spongy bone.
- External part is covered mostly in a fibre membrane, this doesnt cover the ends of the bone where there is cartilage
- Inside the bone there are lots of blood vessels and nerves
- the middle of the bone is compact with a hole in the centre, in this cavity is bone marrow
What do the size/amount of the pores depend on?
Age, health, nutrition, sex of the patient
The fibre membrane covering the majority of the outside of the bone is called what?
Periosteum
Which part of the bone transmits pain signals to the brain?
The periosteum as there is a lot of nerve simulation in the periosteum
What is the central hole of the bone called?
The medullary canal/cavity
What is the membrane called inside the medullary canal (inside hole of bone)?
The membrane is called the Endosteum
What is the bone structure like for compact bones?
Osteon, concentric layers of mineralised bone matrix (like a telescope)
What is the structure of spongy bone?
Trabeculae, they are lamellae arranged as rods or plates
Why does the balance of spongy and compact bone work well?
This balance works well as the spongy bone is less dense and compensates for the added weight of the compact bone
What is at the centre of the osteon structure? And how wide is it?
The osteon central canal, 20 (mu)(*10-6) m
What is inside the central canal of the osteon structure?
Blood vessels and nerves
What are the very thin canals in between the layers of the osteon?
Canaliculi
What do the canaliculi do in the osteon structure?
They transmit info because within these channels are cells and blood flow, these are microcanals
What part of the bone provides the strength and hardness, but also has brittle properties?
The inorganic part
Which part of the bone provides the flexibility and why?
The organic part; as its made up of collagen which has a unique structure making it flexibile
What type of structure does the collagen molecule have?
A triple helix structure, with three chains of proteins
What are the three chains of proteins (amino acids) of the collagen called?
- proline
- hydroxyproline
- glycine
What are the collagen fibres made from?
The three chains of proteins twist together to form the collagen molecules. The collagen molecules form the collagen fibrils, and then form the collagen fibres.
The collagen fibres are relatively short, but have what property?
As the collagen fibres are polymers, they are extremely flexible
What are the different sides of the collagen fibres made up of?
Inorganic and organic parts
What does the inorganic part of the collagen fibre form?
The inorganic part, the ceramic made up of mostly hyroxypatite forms hydroxyapatite crystals that nucleate and grow in specific positions in order to form a mineralised matrix
How does the collagen become a mineralised matrix?
Collagen is an unmineralised matrix, but when hydroxyapatite crystals form on the top of it, it forms a mineralised matrix
What does the mineralised matrix of the collagen provide?
It provides the flexibility, strength and hardness
What are the three main types of bone cells?
- osteoblasts
- osteoclasts
- osteocytes
What are osteoblasts?
- They form the bone matrix
- They have only one nucleus-mononucleated cells
- They arrange themselves in lines
- They are formed by the bone marrow, when stem cells differentiate into osteoblasts
What are osteoclasts?
- They are large cells
- They are multinucleated
- They stay on the surface or the bone
- They are produced by white blood cells
- They detect any cracks or defects inside the bone structure and dissolve/breakdown the bone and reabsorb the bone
What are osteocytes?
- They are osteoblasts that have been embedded in the bone matrix; they transformed into osteocytes
- they are extremely smart cells, they regulate all processes for bone formation and resorption
- they have extension that allows them to communicate with eachother
- they are generally located in small channels and pore
- they regulate calcium concentration aswell as oxygen levels
- they get all nutrients from the blood vessels
What are the black dots/pores called?
lucunae
Why can bone be remodelled for our entire life?
Due to the three main bone cells; osteoblasts, osteoclasts, and osteocytes
As soon as the osteocytes identify stress within the bone, what do they do?
They transmit signals in order for the osteoclasts to move to the localised area
Once in the localised area, what do osteoclasts do?
Once in the localised area, osteoclasts produce enzymes (acid phosphate) to absorb the bone, starting from the central canal area
After the damaged bone is removed, what happens next?
After the damaged bone is removed, osteoblasts locate and form new bone, starting by depositing a layer of collagen giving the un-mineralised bone matrix
What do osteoblasts deposit on top of the collagen, once the damaged bone is removed?
The osteoblasts then deposit enzymes (hydroxyapatite enzymes) on top of the collagen layer, which facilitate the generation of bone, forming mineralised bone structure
Even if no cracks/defects are present, what percentage of the bone is remodelled each year?
5-10%
If osteoblasts become trapped in the bone matrix, what do they become?
osteocytes
What causes osteoporosis?
This is caused when the rate of bone formation from osteoblasts is lower than the rate of bone resorption from the osteoclasts. This depends on several parameters, any stress or microstress/loads will be communicated towards these sites, and improve bone formation- this is why physical activity is important
What was found for bedridden patients that had no load on the bones?
It was shown that bedridden patients that had no load on the bones would loose mass as the bone density will decrease.
Why would the bone density of bedridden patients decrease?
This is because the remodelling process of the bones becomes weakened. The trabecula structure becomes very weak. This is why it is important for the patients to do some exercise so that the osteocytes feel some stresses/loads continuously
What will happen if you do a lot of physical exercise?
If you do a lot of physical exercise you will increase in mass, as the trabecula will become thicker, the osteons will become larger so your bone mass will be higher
What is stress shielding?
A lot of materials used for bone substitution are titanium alloys, stainless steels etc. These metals have very different mechanical properties to the bone. The Youngs Modulus of these materials is much higher than that of the bone. For this reason, when using these metals, the load is taken by the bone substitute, meaning that the osteocytes will not sense the stresses as the bone doesn’t take the majority of the load. This means bone remodelling is slower, and patient loses bone mass.
