Bone tissue Flashcards
main functions:
- mechanical support
- movement, protection
- fat and mineral storage (cal, phos.)
- encloses red bone marrow (hemopoiesis- production of blood cells)
primary bone tissue: features
(immature/ woven)
- temporary -> replaced by mature
- irregular array collagen fibres
- low mineral content
- high proportion of oseteocytes
secondary bone tissue: features
(mature, lamellar)
- collagen fibres arranged in lamellae (thin plate-like structure)
main parts of long bone:
- diaphysis (shaft) with medullary cavity
- epiphysis (ends)
- metaphysis (middle) with epiphyseal plate
(a)vascular? for? major blood supply in long bone
- highly vascular, allow growth and change
- epiphyseal A
- metaphyseal
- nutrient (distal/ proximal) - mid shaft
- periosteal
osteogenic cell: features/ location
unspecialised stem cell, can undergo cell division
- for growth/ remodelling
- inner portion of periosteum, endosteum, blood vessel canals
osteoblast cell: features/ location
- for synthesis of organic extracellular matrix, influence inorganic components’ deposition
- only on the cell surface (cuboidal/ columnar/ squamous)
- when completely surrounded by matrix = osteocyte
osteocyte cell: features/ location
- maintain bone matrix
- respond to mechanical forces, lay down new/ remove matrix
- in lacunae (cavities) within/between lamellae
- communicate to other osteocytes via canaliculi (small canals) -> processes travel through
osteoclasts: features/ location
- stimulated by the parathyroid hormone (indirectly) and inhibited by calcitonin (thyroid gland)
- bone resorption (breaking down)
- uses lysosomes -> matrix
- large, multinucleated, motile, phagocytic, ruffled border (invaginations)
- fusion of monocytes/ macrophages
- attached to bone matrix (tight seal)
compact bone structure: general features
Haversian system/ osteon
- cylindrical unit (concentric lamellae bone matrix) around central canal
- osteon parallel to long axis of bone
- 1-2 capillaries, lymph vessels and nerves
compact bone structure: between/surround Haversian systems features
between: interstitial lamellae/ outer-circumferential
surrounded by cementing substance: mineralised matrix, few collagen fibres
compact bone structure: Volkmann’s canals
perpendicular to Haversian canals, transversely from periosteum -> endosteum, connecting osteons
- blood vessels
spongy bone structure: features
- no osteons, lamellae in irregular lattice of thin columns (trabeculae)
- spaces in btw contain red and yellow bone marrow
- each trabecula-> osteocytes (in lacunae)
- blood supply directly form surrounding blood vessels
difference between periosteum and endosteum: features
Periosteum:
- tough sheet, outer surface of bone (excl. art cartilage)
- outer (fibrous) layer DICT
- inner layer: osteogenic
Endosteum:
- thin membrane, lines internal cavities within bone
- single layer: bone-forming cells, lil ct.
bone formation: before birth
intramembranous and endochondral
bone formation: after birth
length and width
features: intramembranous growth
flat bones of skull (parietal, frontal), mandible
- apposition (growth) on tissue within embryonic connective tissue membrane (mesenchyme)
- bony tissue will develop directly from mesenchyme
intramembranous growth: development stages (formal)
development of ossification centre –> calcification –> formation of trabeculae –> development of periosteum (stimulates compact bone)
endochondral ossification: features
- cartilage first -> replaced with bone
- more common
endochondral ossification: stages of development (formal)
(cartilage model) hyaline cartilage covered in perichondrium (DICT layer) -> interstitial/ appositional cartilage model growth –> periosteum develops (primary ossification centre) —> dev. medullary cavity –> dev. secondary ossification centres –> formation of articular cartilage and epiphyseal plates
intramembranous growth: development stages (informal explanation)
mesenchyme differentiates: osteoblasts, activated -> patches of bone matrix- ossify, merge= trabeculae (spongy bone), blood vessels help, periosteum forms (new osteoblasts outside)-> make compact bone
endochondral ossification: stages of development (informal explanation)
mesenchymal cells: differentiate later in chondrocytes–> calcify and kill cells, nutrient artery (feeds inside) cells differentiate= osteoblasts –> make bony matrix, (primary ossification centre) –> moves towards ends of bones (epiphyses)
secondary ossification centre- ossification from surface which penetrates deeper –> cartilage will only stay at metaphysis
growth in width: features
appositional growth (new layers) of bone tissue on pre-existing bone surface (under periosteum) = increase in width - osteoclasts also on endosteum surface remove bone -> expand medullary cavity
bone growth always regulated
growth in length: features
interstitial growth (length) via formation of new cartilage within existing cartilage mass
growth in length: epiphyseal plate zones
- resting cartilage: connects cartilage to bone (epiphysis)
- proliferating cartilage: new chondrocytes- matrix grows/ stack cartilage, push closer to bone side- will die
- hypertrophic cartilage: mature chondrocytes enlarge leaving large spaces
- calcified cartilage: where cartilage is replaced with bone tissue
leaves epiphyseal line
danger of bone fracture in children:
- this cartilage-> bone growth will stop during teens once all cartilage is replaced
- fracture prematurely disrupts growth/ blood supply = early ossification (shorter)
bone remodelling: how?
- stress to periosteum of bony prominences –> osteoblasts activation (stimulate more bone tissue)
- stronger bones
- create more ridges for muscle attachment
- no stress= loss of bone tissue
Wolff’s law
bone is healthy person/ animal will adapt to the loads it is placed under
eg of bone remodelling:
Patagonia skull modelling
- bandaging skulls
- culturally beautiful
bone repair:
fracture:
- Heamatoma (blood collection outside bl. vessel) - swollen
- -> once cleaned up temporary fibrocartilaginous callus forms (quick framework)
- -> replaced by bony callus, osteoclasts clean up
- -> bone remodelling (try to fix bump)
osteoporosis:
more likely in older female
- after menopause, sharp decline of oestrogen
- brittle bones, easier to break bones
- really slow recovery
- Vitamin D and calcium good, active lifestyle too
