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
