Bone 1 Flashcards
How is the skeleton a dynamic living tissue
Respond o body demand changes for minerals eg pregnancy lactation
Haematopoiesis done by skeleton spec in bone marrow
Bone needed for Ca homeostasis
Mineral store involved in acid-base balance maintenance as release mineral salts into blood that act as buffer
Ltd fat storage in BM too
Topographical classification
Cranial skeleton
Post cranial skeleton
(Axial, appendicular)
Ontogeny based classification
Somatic (form in body wall)
Visceral (form from brachial arches)
Phylogeny based classification
Preformed in cart
Ossify directly in fibrous CT ie flat bones
Class of individual bones
By shape: Long Flat Irregular Short
Bone components
Organic (dry 30-35%, live 30%)
Inorganic (d 65/70%, live 45%)
Water (d 0, live 25%)
Inorganic component
Mainly Ca and P in form of Calcium hydroxyapatite small amount of other salts eg CaF2 CaCO3 MgF2
Responsible for rigidity
If removed bones become bendy
Organic component
Mainly C1 95%
Some amorphous GS
C gives strength and resilience
If removed bones become brittle
Woven bone
Immature form
Primary bone tissue
C fibres laid in random orientation, not aligned along stress lines
Produced in rapid osteoid production eg foetal development fracture repair too
Lamellar bone
Mature replacement of woven in 2 forms compact & cancellous(spongy)
C fibres form regular pattern in cancel lamellae parallel in compact form concentric sheets around vascular channel
Cell types
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
Osteoprogenitor cells
Mesenchymal cells lining bone cavities found in periosteum endosteum haversion channels and Volkmann canals
Differentiate in response to stimulus and give rise to bone producing cells
Osteoblasts
Bone producing cells
Synth organic part of bone matrix (osteoid) and facilitate matrix mineralisation
Cuboidal shape basophilic cyt when active look like epithelium
Act as partial barrier
Extensive rer and Golgi as active pro synth and excretion
Why is osteoblast barrier fx key
Osteoblast inhib
Sep ECF and bone fluid so mineral concs can be regulated
Osteocytes
Mature osteoblasts embedded in own secretion occupying lacuna
key in matrix maintenance
Stellate with less rer and Golgi as reduced metabolic activity than osteoblasts more condensed chromatin - less active DNA
How osteoclasts communicate
Numerous filopodia in small canaliculi that interact with each other via gap jctn allowing hormone and metabolite transport between cells
Osteoclasts
Myeloid progenitor lineage
(Monocytes in blood migrate to tissues and become osteoclasts or macrophages)
Giant mobile multinucleated cells acidophilic cut some rer and Golgi
Abundant mitochondria and lysosomes reflect bone resorption fx
How osteoclasts carry out bone resorption
In howships lacunae (make themselves) on bone matrix surface
Form enclosed area between themselves and matrix by folding membrane many times to create micro environment ideal for bone resorption
Micro environment conditions for bone resorption
Low pH
High proteolytic enz conc
Where is mineralisation detrimental
Most area of the body
What inhibits mineralisation of soft tissue
Pyro phosphate (PP)
How C1 is involved in mineralisation
C1 fibrils produced and packaged in rer and Golgi
Secreted by osteoblast at cell surface producing osteoid
In maturation phase C fibrils form polymers and line up forming hole zones.
How long is the maturation phase
Several days
How is amorphous CaPO4 salts involved in mineralisation
The salts precipitate into the hole zones formed
Forming initial mineralisation sites
Ca salt deposition maybe accelerated by osteoblast ability to conc them in intracytoplasmic vesicles which are released into the ECM along with high alkaline phosphatase (ALKP) levels
ALKP fx
Breaks down PP allowing for mineralisation
Calcitonin as bone mineralisation regulator
Hormone secreted by C cells of the thyroid gland (tones down blood calcium)
Inhib osteoclast fx so reduce bone resorption and reduce Ca released into plasma
Parathyroid hormone (PTH) role in bone mineralisation regulation
Hormones secreted by chief cells of PTgland
Interact directly with osteoblasts and increase RANK ligand and reduce osteoprotegerin (OPG) release
Indirectly stimulate osteoclast activity leading to incr bone resorption
2 mechanisms of bone formation
Endochondral ossification
Within a membrane of CT
Skeleton fx
Structure & support for the body
Permit locomotion
Scaffold for muscle and teeth attachment
Carries vital organs and so is optimised for protection in some areas but this an compromise movement eg skull
Other areas balance between movement and protection eg thorax
Intramembranous formation
Source of most flat bones
Many primary ossification centres form in fibrous CT when mesenchymal cells diff into osteoblasts which produce osteoid and mineralisation ensues
Cells trapped and mature. Islands of dev bone spicules form and after a while fuse and woven bone is produced with Areas of trapped CT
In intramembranous ossification how do blood vessels etc permeate it
The trapped CT areas are penetrated by blood vessels and undiff mesenchyme cells which give rise to the BM
Bones grow radially and fuse replacing original CT
New born skull formation
Fontanelles are soft areas of the skull that correspond to unossified areas. Post birth bone formation in flat bones incr and outstrips bone resorption esp at int/external surfaces forming 2 compact bone layers with a cancellous centre (diploe) other mesenchyme cells give rise to end/periosteum
How is periosteum of skull specialised
Outer fuses with the deep scalp layers
Inner constitutes the dura mater (outermost brain membrane)
Endochondral ossification
Mainly responsible for short and long bone formation
Endochondral ossification step 1
Small hyaline cart model formed
Endochondral ossification stage 2 internal
Chondrocytes in shaft enlarge, surrounding cart resorbed and only thin trabeculae of cart left which are calcified. Therefore death of Chondrocytes leaving large spaces.
Endochondral ossification stage 2 external
Simultaneously perichondrium of shaft dev osteogenic potential becomes periosteum and bone collar formed around shaft by intramembranous ossification
This adds to degen of Chondrocytes cutting of nutritional supply
Endochondral ossification stage 3
Blood vessels invade empty spaces via channels in the bone collar made by osteoclasts
Primitive mesenchyme cells follow and diff into osteoblasts and blood forming cells of BM
Endochondral ossification stage 4
Osteoblasts form layer on the surface of calcified cartilage remnants and start to produce woven bone
Endochondral ossification stage 5
2 ends of cartilage model now sep by primary ossification in centre of shaft
2 cart ends grow in diameter forming epiphyses and each develop a secondary ossification centre
Endochondral ossification stage 6
Interface between shaft and epiphysis that continues to undergoes regressive changes then ossification leading to elongated bony diaphyseal shaft formation with semilunar cartilage epiphysis at each end
Interphase between the two is the growth plate
Endochondral ossification stage 7
Within GP cartilage proliferate continuously leading to bone elongation
Endochondral ossification stage 8
At each end a layer of hyaline remains which becomes art cart
Endochondral ossification stage 9
Woven bone remodelled under influence of fxal stress into lamellae bone formin cortical layer of compact with cancellous centre
