Bone tissue Flashcards
State the functions of bone tissue
- Structure
- Mobility
- Support
- Protection
- Store for minerals (mainly calcium)
- Blood cell production
- Fat production & storage
(Many functions = lots to go wrong - needs good upkeep)
Common features of long bone
ends = epiphysis
middle = diaphysis
between these is a widening = metaphysis which separates growth plate from diaphysis
- endosteum = inner layer
- periosteum = 2 layers around outside
- outermost is where tendons/ligs attach
What is the make-up of bone
Matrix of collagen fibres and ground substance that becomes calcified to give bones their firmness
(25% water, 25% collagen, 50% crystalized mineral salts - mainly calcium)
so bone is
- hard yet brittle
- light per unit of volume
Name the two types of bone tissue
Compact = 80% of bone mass
- solid hard layer (strong in longitudinal axis)
- external layer of all bones
Spongy = 20% of bone mass
- honeycomb network
- inner parts of axial skeleton + ephiphyses of long bones
- light
- good shock absorber
Describe Compact bone + its formation
- dense + less flexible - hard external layer of all bones
> Formation - osteoblasts lay collagen down in criss-cross around blood vessels
- 1 ring = lamellae
- many lamellae = osteon (a.k.a haversian system)
- many osteons form to give compact bone its strength
- between osteons = interstitial lamellae
- between lamellae = lacuna of extracellular fluid & osteocytes
- Osteocytes = mature bone cells (osteoblasts that have walled themselves in)
- projections called canaliculi allow osteocytes to communicate & regulate bone tissue + nutrients
Describe Spongy bone and its formation
Spongy/ Trabecular/ Cancellous Bone
- Lattice-like
- Collagen fibres = laid down on stress lines = trabeculae (little beans)
- able to cope with multi-directional stress - distributes to longitudinal axis of compact bone
- light
- osteocytes reside in lacunae on surface of trabeculae
(gain nutrients via canaliculi = projections which pick up blood in medullary cavity)
what are the 4 bone cell types
> Osteogenic (osteoprogenitor) cell - undifferentiated - develops into osteoblast - found in endosteum + inner periosteum > Osteoblasts - builds matrix and collagen fibres (can't divide) - generally on outside of bone > Osteocytes = mature cells in lacunae - maintain bone tissue > Osteoclasts - clear bone cells - developed from monocytes - phagocytosis (ruffled border to stick to edge + form seal, releases enzymes to kill bone cells, absorbs debris)
Define Remodelling and Coupling of bone
Remodelling = constant process of building + destroying bone cells Coupling = Balance between building and destroying (uncoupling = loss of balance)
Describe Bone growth
- Cartilage grows at outer end of bone
- cartilage on inner end is replaced by bone
- remodelling - changes in width - resorbed at wider parts/ added at thinner parts (appositional growth)
Occurs in women til around 18-19 years
men til around 18-25 years
What can go wrong with bone growth
- Osteoporosis- low bone density
- Osteogenesis imperfecta - brittle bone disease (not enough collagen)
- Paget’s disease (bone = replaced faster than usual - doesn’t form as well so it weaker)
- Bone cancer
- Bone infection
Blood supply to the bones
> periosteal arteries - periosteum and outer osteons of compact bone > nutrient arteries via nutrient foramen - medullary cavity and osteons of inner compact bone > Metaphyseal arteries - spongy bone and marrow in metaphysis > Epiphyseal arteries - spongy bone and marrow in epiphysis
Affectors of remodelling
> Age
- osetopenia = demineralisation of bone from 40 years on, accelerated by menopause
- osteoporosis = accelerated demineralisation
Mechanical stress
- weight bearing allows development + healing
- loss of activity = weaker bone (50% loss in 12 weeks)
Genetics
Environment
Nutrition - phospate + calcium = key in blood clotting so bone may be destroyed if levels in blood are low
Hormones - hgh, sex hormones, parathyroid hormone, calcitonin
Bone disorders - developmental
> Agenesis = limb doesn’t form/malforms
osteogenesis imperfecta = brittle bone disease
spina bifida = spinous processes malform - exposing spinal cord + fluid
achondroplasia = dwarfism
Bone disorders - remodelling + nutritional
Remodelling > age > hormone levels > calcium + phosphate levels > Mechanical stress + activity
Nutritional
> rickets - lack of vit d
> osteomalacia
> scurvy - lack of vit c
Bone disorders - Endocrine
> Gigantism - too much hgh pre-puberty
acromegaly - over dense bone = >hgh post puberty
pituitary dwarfism = too little hgh
hyper/hypothyroidism = too much/little calcium
post-menopausal osteoporosis
Bone disorders - ageing
> osteopenia
- normal decrease in mineral levels due to osteoblast ability decreasing with age
osteoporosis = accelerated decrease in bone density
- Primary = high risk categories e.g women/elderly/non-weight bearers
- Secondary = due to disease/malnutrition
* Modifiable factors = smoking/alcohol/caffeine/protein/calcium/sunlight levels
How are fractures named
- Severity
- Shape
- Position
- Name
State the types of severity classification in fractures
- open/compound = through skin
- impacted = breaks forced into each other
- comminuted = many pieces
- closed/simple= skin is intact
- displaced - fragments have moved usually due to muscle spasm
State the types of shape classification in fractures
- spiral - twisting forces
- oblique - twisting with force applied
- greenstick - splinters rather than breaks - usually kids
- depressed - disappears down - usually in skull
- transverse - straight across
State the types of position and name classification of fractures
Position
- distal/proximal
- shaft
- neck
- epiphyseal
Name
Colle’s - distal radius
Potts - ends of malleoli
Describe the bone healing after fracture
- hematoma formation (72 hours but clear up = 3/52)
- bleeds - clots within 6-8 hours and cells die
- inflammation - dead bone + debris is cleared by phagocytosis
- ANGIOGENESIS - new capillaries grow into area - Fibrocartilaginous callus forms (~3 weeks)
- fibroblasts invade procallus and lay down collagen
- chondroblasts produce fibrocartilage - Formation of bony callus (takes 3-4 months)
- osteoblasts create spongy bone that joins bone ends
- fracture site = firmly held - Bone remodelling (up to 1 year)
- compact bone replaces spongy bone
- surface = remodelled but lump may remain
Rate of fracture healing is affected by:
> Type of fracture > Site of fracture + vascular supply > age > movement > separation of bony ends > infection > bone pathology
Spiral fractures UL = union in 3/52 and consolidated in 6/52 LL - union - 6/52, consolidated - 12/52 Transverse fractures UL union - 6/52, consolidated - 12/52 LL union - 12/52, consolidated - 24/52
Symptoms of fracture
> Pain + tenderness > swelling + bruising > deformity/angulation > impaired function > shock
Treatment of different fractures
> Closed (simple) - realigned + immobilised - rehab if necessary > Open (simple) - open reduction and internal fixation - rehab for damaged soft tissue > Open (complex) - open reduction + external fixation - rehab for damaged soft tissue
Complications of fracture healing
> delayed/mal-union
avascular necrosis
sudeck’s atrophy - disturbance to SNS
compartment syndrome -swelling cuts of blood
Volkmanns ichaemia - pressure in forearm
myositis ossificans = bone laid in muscle
blood vessel/nerve/visceral damage
tendon injury
fat embolus - yellow bone marrow in blood stream -stroke/heart attack risk
OA
growth impairment
