16-09-21 - MS System: Bones Flashcards
What are the functions of bones?
- Enables movement through attachment of muscles
- Provides protection
- Structural support
- Storage of minerals – primary calcium, phosphate, and magnesium
- Bone marrow is the site of haematopoiesis (blood cell formation)
What does bone consist of? And what gives it its strength?
- Collagen fibre framework in mucopolysaccharide-rich semisolid gel (ground substance) – gives bone tensile strength (ability to withstand tension)
- Bone is hardened by precipitation of Calcium Phosphate (hydroxyapatite) crystals within its matrix – this gives bone its compressional strength (ability to withstand compression)
- Bone is made from osteoblasts, osteoclasts, and osteocytes (cells)
What are the different parts of the long bone in this diagram?
What is each part made of?
What is each part for?
- Medullary cavity at the centre of the bone
What are the 2 major kinds of bone found in the long bones?
What do they do?
- Trabecular/cancellous (spongy/porous) – Gives supporting strength to the ends of the weight-bearing bone.
- Cortical (solid) – Runs down the outside of the bone and forms the shaft of the long bone.
- Provides stiffness and strength
- Transfers forces generated on the weight surface of the long bones
Where are trabeculae found?
What do they do?
How are they generated?
- Trabeculae are laid along the lines of stress in the head of long bones
- They allow for the distribution of stresses on the bone heads to the shaft (diaphysis)
- Without them, bone heads would succumb to forces placed on them and shatter.
- They are generated as the bone grows and is stresses through activity
How is blood supplied to and from bones and why?
How close are cells to these blood supplies?
- Haversian canals carry blood along the axis of the bone (parallel)
- Volksman canals carry blood perpendicularly
- Majority of the cells in the bone are in close contact to the blood supply, but osteocytes are not.
Cortical bone:
- What are its anatomical/functional units?
- What runs through it?
- How are its cells arranged?
- What is its structure like and what minerals does it require to stay strong?
- The anatomical/functional units of cortical bone are osteon
- Haversian canals contain blood vessels that carry blood along the bone
- Osteocytes are arranged in concentric circles (like onions) around blood vessels in haversion canal
- Each layer contains collagen fibres, which can be oriented differently for each layer, making the structure flexible.
- Hydroxyapatite is needed to add strength to the bone
- It is now strong and flexible enough
Trabecular/cancellous bone:
- What are its anatomical/functional units?
- Composition compared to cortical bone
- Function
- Anatomical/function units: Trabeculae
- Fewer lamellar layers in trabecular region than cortical
- Weaker and more flexible than cortical bone
- More open, less dense and site of haematopoiesis in bone marrow
What is the composition of bone matrix?
- Organic matrix
- Mostly made from protein fibres called collagen
- The collagen is organised in parallel arrangement in both cortical and trabecular bones
- Inorganic matrix
- Made from crystallised mineral salts like hydroxyapatite
- Made from water
What are common disorders regarding the bones?
What causes them?
What does this lead to?
- Rickets – caused by a vitamin D deficiency.
- The body can’t absorb Calcium and form hydroxyapatite.
- Scurvy – Vitamin C deficiency – lack of proper collagen formation
What are osteoblasts?
How are they formed?
What do they do?
What can be their fate?
- Mononucleate cells, derived from osteoprogenitor cells (stem cells).
- Line the surface of the bone
- When stimulated to form bone, will deposit organic matrix (collagen) and then hydroxyapatite
- Some osteoblasts become entombed in the matrix during this process and turn into osteocytes (mature bone cells)
What are osteoclasts?
What do they do?
How are they controlled?
- Multinucleate cells created by individual cells fusing
- Forms a sealing zone on the edge of the bone matrix, releases H+ ions and hydrolytic enzymes in order to dissolve the material, liberate calcium and break down the extracellular matrix.
- Regulated by hormones (e.g oestrogens) and osteoblasts.
What are Osteocytes?
How are they formed?
How do they communicate?
What do they do when these structures are damaged?
- Osteocytes are mature bone cells.
- They are formed when osteoblasts become entombed in the matrix during bone formation
- They communicate via finger like structures in the canaliculi
- If the canaliculi become damaged, osteocytes will attract the attention of osteoblasts to repair them.
Why is bone described as being a dynamic tissue?
- It is dynamic because it cycles through being reduced to its primary components via resorption to being built back up again from these components by osteoblasts
How is bone formation and resorption balanced?
What can cause this to become unbalanced?
- Equilibrium between osteoblast and osteoclast activity is controlled by signalling between the different cells in bone and via the actions of hormones such as Calcitonin and Parathyroid Hormone (PTH)
- Calcitonin – Reduces activity of Osteoclasts and reduces Calcium blood levels
- PTH – Increases activity of Osteoclasts which increases Calcium blood levels
What is the trabecular bone remodelling for?
How is it triggered?
Describe the process. QRRO
- The trabecular bone remodel cycle is triggered by microdamage or hormonal responses
- It is generally scheduled repair/turnover
- The 4 stages of the cycle are:
- Quiescence
- Resorption by osteoclasts
- Reversal
- Osteoblasts laying down new bone
Give a description of the cortical bone remodelling cycle and how it relates to the trabecular bone remodelling cycle. => builders with waterworks
- The remodelling cycle for cortical bone is more complex than the remodelling cycle for trabecular bone as cortical bone is more solid.
- To start, a cutting cone is developed by osteoclasts at the resorption front.
- The osteoclasts tunnel into remote regions of bone via haversion canals
- Osteoclasts than then drill down behind haversion canals and surface cells
- The release H+ ions and hydrolytic enzymes to dissolve the bone matrix (broken down components released into extracellular fluid)
- Osteoblasts will then rebuild and lay down new matrix
- Some osteoblasts will become entombed in the new matrix and become osteocytes.
- A closing cone is formed by red stained osteoid lined with osteoblasts.
What can cause bone mass and density to increased = 1
decreased = 4
What is Wolffs law?
- Bones mass and density can be increased by excessive mechanical stimulation and increased stresses, such as running.
- Bone mass and density can decrease because of non-weight bearing (immobilisation from injury ie atrophy)
- Sex-hormone deficiency (e.g menopause)
- Endocrine/nutritional deficiency (inability to absorb calcium because of lack of vitamin D, can’t form hydroxyapatite – rickets)
- Natural aging process
- Wollf’s law – Bone adapts to load under which its placed (ie more load placed on bone, the more bone will form within limits)
Describe the age-related change in bone mass graph for men and women.
- Ages 1-27 – Attainment of peak bone mass
- Ages 27-40 Consolidation of peak bone mass
- More than 40 – Age related bone loss
- Woman go through menopause at around 50, which leads to an accelerated decrease in bone mass.
- At around 60, women will pass the fracture threshold for bone mass, which makes them more susceptible to fractures/breaks.
- This is indicated when they suffer a fracture or break from a relatively minor fall
What are the differences between normal and osteoporotic trabecular bone?
What are consequences.
- In Osteoporotic bone, there are significant breakages and gaps between the trabeculae compared to the normal bone
- If trabeculae are not present, or are weak and thin, they will not direct stress well away from the head of bones, making them more susceptible to fractures and breaks.
How does bone initially grow in foetuses?
What is it replaced by?
NAME OF OSSIFICATION FOR LONG VS FLAT BONES
Where is the primary centre of growth?
- Initially a cartilage model is formed by chondroblasts and reshaped by chondrocytes (mature cartilage cells)
- This cartilage model is replaced by bone via ossification
- Endochondral ossification for long bones and intermembranous ossification for flat bones
- During foetal endochondral ossification, the primary centre of ossification is in the bony shafts known as diaphysis
- This primary centre is active before birth.
How does bone growth change after birth?
What is the secondary center of growth?
What is between the primary and secondary centers of growth?
Under what circumstances will growth continue?
- After birth, bone begins to develop in the ends of long bones in the epiphysis
- The epiphysis is the secondary center of ossification
- The epiphyseal plate is cartilage that exists between the primary and secondary centers of ossification and is located in the metaphysis of long bones,
- Bone is laid down in the diaphysis and the epiphysis
- As long as the epiphyseal plate of cartilage is between the 2 centers and active, and new bone is laid down at the centers of ossification, the bone will increase in length
Describe the process of bone growth at the epiphyseal plate.
RGHCO
What occurs to bones by the end of puberty and why?
- At the end of the puberty, the epiphyseal growth plates fuse, leaving the epiphyseal line
- The epiphyseal growth plate of cartilage is no longer active and the bone forms.
How long do fractures take to heal?
What does a fracture lead to?
What is the proces of fracture healing?
- Fractures take 2-4 weeks to heal, depending on age, severity and position of fracture
- A fracture leads to inflammation and an increase in blood flow
- This leads to callus formation – osteoblasts quickly form woven bone to bridge the gap, which is weak as the collagen fibres are not organised or mineralised well.
- Lamellar bone is then laid down – collagen is now organised in regular sheets to give strength and resilience
What are the 6 different types of bones? What are examples of each?
At the time of birth, what stage of growth in long bones has typically been achieved?
Mineralisation in the diaphysis only
