Bone Flashcards
what is the endosteum and the periosteum?
tissue lining the internal (endo) and external (perio) surfaces of bone containing osteogenic cells
what are canaliculi?
thin cylindrical spaces that penetrate the matrix and allows the exchange of materials between osteocytes and capillaries
what organic components do osteoblasts synthesize?
type 1 collagen, proteoglycans, and glycoproteins
what do active osteoblasts look like compared to inactive?
active: cuboidal/ columnar w basophilic cytoplasm
inactive: flattened w/ less basophilia
what is in a lacuna where osteocytes are found?
osteocyte
small amount of ECM non-calcified
what is an osteoid?
new uncalcified matrix
what is bone apposition?
process of secreting new matrix and calcifying it
how to osteocytes communicate?
gap junctions + through exchanging material in the small amount of matrix b/w them
what is in a osteocyte?
condensed chromatin
reduced rER
golgi
what are the depressions osteoclasts are found in during active resorption?
Howship’s lacunae
what are the 2 borders of the osteoclasts during active resorption?
ruffled- facing bone marrow that is folded irregularly
clear zone- site of adhesion b/w cell and bone matrix (sealed)
how do osteoclasts break down bone?
- secrete collagenase and other enzymes into microenvironment
- pump protons into the pocket = acidic
- dissolves Ca+ and digests collagen
what controls osteoclast activity?
hormones and cytokines
what do calcitonin receptors do to osteoclasts?
when activated, they turn off the osteoclasts in order to lower the calcium level in the blood
what does parathyroid hormone do to osteoblasts and osteoclasts?
osteoblasts have a parathyroid receptors
when activated they produce a cytokine (osteoclast activating factor) that stimulated osteoclasts
INCREASES blood Ca+
what accounts for 50% of dry bone weight?
calcium and phosphorus (hydroxyapatite crystals + calcium phosphate)
what gives bone harness and resistance?
minerals+ collagen fibers
what are sharpey’s fibers?
collagen fibers that penetrate bone matrix and bind the periosteum to the bone
what are the 2 layers of the periosteum?
outer layer- collagen fibers + fibroblasts
inner layer - osteoprogenitor cells (fibroblast-like)
what makes up the endosteum?
a single layer of osteoprogenitor cells
what are key features of primary bone?
random deposition of fine collagen fibers, lower mineral content, and higher proportion of osteocytes
where can you find primary bone in an adult?
tooth sockets
sutures of the skull
some tendon insertions
what is the typical organization of secondary bone?
collagen fibers are in lamellae (‘layers’)
lamellae are parallel and concentric around a vascular canal
the lacunae containing the osteocytes are between the lamellae
what are Haversian systems?
concentric lamellae between the inner and outer circumferential lamellae
what are interstitial lamellae?
irregularly shaped areas between haversian systems
what is the basic organization of the haversian system or osteon?
lamellae are laid down successively from the periphery inward
fiber are arranged parallel to each other in a helical course within a lamellae
fibers change direction w/ each successive lamellae
how do the central canals in the osteons communicate w/ marrow cavities, periosteum, or other canals?
transver or oblique Volkmann’s canals (perforate lamellae)
what bones are formed by intramembranous ossification?
frontal and parietal bones
part of occipital and temporal bones
mandible
contributes to growth of short bones and thickening of long bones
what is the basic process of intramembranous ossification?
- primary ossification centers form
- cells differentiate into osteoblasts
- osteoblasts make matrix that calcifies
- developing bone forms walls that make cavities
- ossification centers grow and fuse
- bone formation dominates over resorption= compact bone
what bones undergo endochondral ossification?
short and long bones
what are the basic steps of endochondral ossification?
- starts in a piece of hyaline cartilage
- bone collar forms through intramembranous ossification
- the local cartilage undergoes matrix calcification
- blood vessels penetrate bringing in osteoprogenitor cells
- osteoblasts begin laying down bone matrix over the primary ossification centers
- secondary ossification centers appear at the ends (articular and epiphyseal cartilage remains)
- ossification centers leave cavities that fill w/ bone marrow
what are the 5 zones of the epiphyseal cartilage?
(superior to inferior) resting zone proliferative zone hypertrophic cartilage zone calcified cartilage zone ossification zone
what is the resting zone?
hyaline cartilage w/o any changes
what is the proliferative zone?
chondrocytes divide rapidly and form columns of stacked cells
what is the hypertrophic cartilage zone?
large chondrocytes w/ cytoplasmic glycogen
what is the calcified cartilage zone?
the chondrocytes die and the septa become calcified
what is the ossification zone?
osteoblasts form and deposit bone matrix
blood and capillaries and osteoprogenitor cells invade
what are the two mechanisms of calcium mobilization?
- hormone action (calcitonin/ parathyroid)
2. simple ion transfer from hydroxyapatite crystals to the interstitial fluid
what are the two layers of synovial joint capsule connective tissue?
fibrous layer (external) synovial layer (internal)
synovial fluid has a high concentration of what in it?
hyaluronic acid
