Unit 2 Bone Flashcards
structure of bone
connective tissue
mineralized matrix-cells in lacuna
vascularized
functions of bone
support
protection (organs, myeloid tissue)
movement
mineral storage (Ca, PO4)
bone classification
long
short
flat
irregular
long bone
longer than wide
limb bones
short bone
cube-shaped (wrist/ankle)
sesamoid (w/in tendons)
vary in size and number
flat bones
thin, flat, slightly curved
sternum, scapulae, ribs, most skull bones
irregular bones
complicated shapes
vertebrae, hib bones
sutural bones
aka wormian, accessory
random, usually on skull
histological organization
spongy
compact
spongy
cancellous
trabecular
compact
lamellar
cortical
dense
histological preparation
decalcified - preserves cells
ground - preserves architecture
typical long bone structure
shaft, epiphyses, membranes
diaphysis
tubular shaft that forms long axis
consists of compact bone surrounding central medullary cavity that is filled with yellow marrow in adults
epiphyses
ends of long bones that consist of o impact bone externally and spongy bone internally
articular cartilage covers articular surfaces
epiphyseal line
remnant of childhood epiphyseal plate where bone growth occurs
compact bone
dense outer layer on every bone that appears smooth and solid
aka lamellar bone
consists of osteon, canals, canaliculi, interstitial & circumferential lamellae
spongy bone
made-up of honeycomb of small, needle-like or flat pieces of bone call trabecular
open spaces filled with red/yellow marrow
stress resistant
no osteons, but have lamellae, osteocytes, canaliculi
membranes
periosteum
endosteum
periosteum
covers outside of compact
white double-layered membrane that covers external surfaces except joints
contains many nerve fibers, vessels through nutrient foramen
anchoring points for tendons/ligaments
endosteum
covers inside portion of compact
delicate CT covers trabecular of spongy bone
contains osteogenic cells that can differentiate into other bone cells
short, irregular, flat bone structure
thing plates of spongy bone (dipoë) covered by compact bone
compact bone sandwiched between CT membranes
bone marrow scattered throughout
hyaline cartilage covers articular surfaces
periosteum layers
fibrous
osteogenic
fibrous periosteum layer
outer layer consisting of dense irregular CT consisting of Sharpey’s fibers
osteogenic layer
inner layer, contains primitive osteogenic stem cells that give rise to most all bone cells
red marrow
found within trabecular cavities of spongy bone and diploë of flat bones
in newborns, medullary cavities and alls spongy bone
in adults, head of femur, humerus, flab bone diploë, some irregular bones
yellow can convert to red in anemic
four cell types
osteogenic cells
osteoblasts
osteocytes
osteoclasts
osteogenic cells
aka osteoprogenitor, stem
mitotically active stem cells in inner layer of periosteum, endosteum and lining of Haversian canal
when stimulated, differentiate into osteoblasts
osteoblasts
bone forming cells that secrete unmineralized bone matrix called osteoid
begins mineralization of matrix
extend cellular process to maintain contact with other cells as matrix deposited
found on surface of growing bones
osteoid
made of collagen I, ground substance
osteocytes
mature bone cells in lacunae that no longer divide
maintain bone matrix
respond to mechanical stimuli
maintain contact with other cells via canaliculi
osteoclasts
part of mononuclear phagocytic system from bone marrow
derived from same stem cells that become macrophages
giant, multinucleate cells
bone resorption
when active, located in Howship’s lacunae
ruffled borders to increase SA for enzyme degradation
osteon
structural unit of compact bone
consists of elongated cylinder runs parallel to long axis
lamellae
several rings of bone matrix within osteon
contain collagen fibers that run in different directions in adjacent rings
withstands stress and resist twisting
bone stalk found between collagen fibers
Haversian canal
aka central canal
runs through core of osteon
contains vessels and nerves
Volkmann’s canal
aka perforating canal
lined with endosteum that occur at right angles to central canal
connect vessels/nerves of periosteum, medullary cavity, central canal
interstitial lamellae
not part of osteon
some fill gaps between forming osteons
others are remnant os osteons cut by bone remodeling
circumferential lamellae
deep to periosteum, superficial to endosteum
extend around entire surface of diaphysis
prevents twisting
organic components
cells and osteoid
osteoid
secrete by osteoblasts
makes up 1/3 of organic bone
consists of ground substance, collagen fibers
inorganic components
mineral salts
hydroxyapatites
mineral salts
65% of bone by mass
tiny calcium phosphate crystals around collagen
responsible for hardness/resistance to compression
intramembranous ossification
begins with fibrous CT membranes formed by mesenchymal cells
called membrane bones
frontal, parietals, occipital, clavicle
ossification
osteogenesis
process of bone formation
begins in month 2, end in early adulthood
bone remodeling/repair lifelong
endochondrial ossification
bone forms by replacing hyaline cartilage
called cartilage bones
forms most of skeleton
primary/secondary centers
intramembranous ossification steps
- ossification centers are formed when mesenchymal cells cluster and become osteoblasts
- osteoid is secreted, then calcified
- woven bone is formed when osteoid is laid down around vessels, resulting in trabeculae (periosteum)
- lamellar bone replaces woven bone, red marrow appears
primary ossification center
vessels infiltrate perichondrium converting it to periosteum
mesenchymal cells specialize into osteoblasts
endochondral ossification steps
- bone collar forms around diaphysis of cartilage
- central cartilage in diaphysis calcifies, develops cavities
- periosteal bud invades cavities => spongy bone
- diaphysis elongates, medullary cavity forms, secondary ossification centers appear in epiphyses
- epiphyses ossify, hyalin cartilage remains only in epiphyseal plates, articular cartilages
periosteal bud
made of vessels, nerves, red marrow, osteogenic cells, osteoclasts
postnatal bone growth
lengthwise by interstitial (longitudinal) growth of epiphyseal plate
bones increase thickness through appositional growth
bones top growing during adolescence
interstitial growth requires presence of epiphyseal cartilage
epiphyseal plate
maintains thickness
rate of cartilage growth on one side balances by bone replacement on other
epiphyseal plate zones
resting (quiescent) zone proliferation (growth) hypertrophic calcification ossification
resting zone
aka quiescent zone
area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive
proliferation zone
aka growth zone
areas of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing
new cells move upwards, pushing epiphysis away from diaphyses
hypertrophic zone
area of chondroytes flower to diaphysis
cartilage lacunae enlarges and erode, forming interconnecting spaces
calcification zone
surrounding cartilage matrix calcifies
chondrocytes die and deteriorate
ossification zone
- chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction
- spicules eroded by osteoclasts, covered with new bone by osteoblasts
- replaced with spongy bone
- medullary cavity enlarges as spicules are eroded
woven bone
- first bone formed
- can be remodeled into mature spongy or compact
- lower mineral content, higher osteocytes
- irregular orientation of collagen
epiphyseal plate closure
18-25yo, women first
hormonal control
parathyroid
calcitonin
PTH
produced by parathyroid in response to low blood Ca
- stimulates osteoclasts to resorb bone
- calcium released in blood
- PTH ceases in homeostasis
calcitonin
produced by parafollicular cells of thyroid gland in response to high blood Ca
pituitary dwarfism
hypo secretion of GH during childhood, 4’ max
gigantism
hyper secretion of GH during childhood, 8-9’ common
acromegaly
hyper secretion after long bone growth stops
