MS System: Bones Flashcards
Function of bones? (5)
- movement
- protection
- structural support
- storage of minerals
- haematopoiesis - blood cell formation
Structure of bone?
- collagen fibre framework - tensile strength
- calcium phosphate (hydroxyapatite) crystals within matrix- compressional strength
- osteoblasts, osteocytes, osteoclasts
- blood vessels and nerves
- bone marrow
What is cartilage?
similar to bones but not calcified
Parts of a long bone?
> epiphysis - head, articular surface - covered by hyaline cartilage - spongy bone
diaphysis - shaft, hollow cylinder - contains bone marrow in medullary cavity. - nutrient foramen (blood supply) - compact bone
periosteum - fibrous connective tissue sheath covering external surfaces
metaphysics - between epiphysis and diaphysis - region of growth
Cells of periosteum?
- fibroblasts - synthesise collagen
- mesenchymal cells - differentiate into osteoblasts and chondroblasts
- osteoclasts - mature bone cells
Trabecular/cancellous bone?
- spongy
- porous
- supporting strength to weight bearing end of bone
- trabeculae allow distribution of stresses - have a high surface area for metabolism
Cortical bone?
- compact
- forms outside of shaft
- provides stiffness and strength
Blood supply to/from bone?
> Haversian canals - blood along axis of bone
Volkman’s canals - blood perpendicularly
- highly vascularised - majority of cells in very close contact to blood vessels (except osteocytes)
Structure of cortical (compact) bone?
- cells arranged in concentric circles
- collagen fibres in each layer
- fibres in each layer can be orientated differently - flexible
- osteocytes surround h canal in repeating units
- calcium hydroxyapatite to add strength and harden
Structure of spongy (cancellous/trabecular) bone?
- fewer lamellar layer
- less coordinated
- trabeculae create spaces - where haemospoiesis is found - bone marrow
Composition of bone matrix?
- collagen - organised parallel arrangement
- crystallised mineral salts - hydroxyaptite
- water
Osteoblast?
bone forming cell
- covers surface of bones
- becomes trapped as an osteocyte
- deposit organic matrix (collagen) then hydroxyapatite
Osteoclast?
(osteophage) reabsorbs bone matrix by demineralisation - stress and physiological response - large - multinucleated cell - derived from haematopoeitic cells
Osteocyte?
mature bone cell
- formed from trapped osteoblasts
- embedded in lacunae
- relatively inactive
- cell- to - cell communication via projections called canaliculi
- influence bone remodeling
Osteoprogenetor cell?
stem cell population - gives arise to osteoblasts (but also other cells)
Vitamin D deficiency causes?
rickets - failure of Ca+ absorption
Vitamin C deficiency causes?
scurvy - lack of collagen
What controls the equilibrium between osteoblast and osteocyte activity?
signalling between bone cells via hormones
- calcitonin - decrease activity of osteoclasts, decreases blood calcium level
- parathyroid hormone (PTH) - increase activity of osteoclasts, releases calcium ions
Trabecular bone remodeling cycle?
function - deal with micro damage, scheduled turnover, role in calcium regulation
- quienscence - inactivity
- resorption by osteoclasts
- surface exposed to osteoprogenitors - osteoblasts differentiate
- osteoblasts lay down new bone
Cortical bone remodelling?
- cutting cone - osteoclasts reabsorb bone at resorption front
- osteoblasts lay down new matrix - become surrounded and become osteocytes - closing cone
(more complicated process)
Wolff’s law?
bone adapts to the load under which it is placed - weight bearing, orthodontic braces, head binding
What increases bone mass and density?
excessive mechanical stimulation
What decreases bone mass and density?
- non weight bearing
- sex-hormone deficiency - menopause
- endocrine/nutritional disorders
What happens in osteoporotic bone?
spaces between trabeculae increase
