Skeletal System Part 1 Flashcards
primary function of bone and cartilage
support and locomotion/movement
secondary functions of bone and cartilage (3)
protection
mineral storage
hemopoiesis
bone vs cartilage (rigidity)
bone is rigid
cartilage is semi-rigid
both bone and cartilage are derived from
primitive mesenchymal cells
relative strength of each is due to properties of (2)
ground substance and extracellular fibers
cartilage is a — precursor
bone
Cartilage formation begins with
stellate mesenchymal cells
stellate mesenchymal cells differentiate into — —, grow & synthesize (2)
rounded chondroblasts
ground substance & fibrous extracellular matrix
ground substance & fibrous extracellular matrix trap chondroblasts in
lacunae
Further mitotic divisions produce clusters of mature chondrocytes, referred to as
isogenous groups
isogenous groups are separated by
extracellular matrix
territorial vs. interterritorial
Cartilage surrounded by
perichondrium
perichondrium
peripheral zone of dense connective tissue, containing fibroblasts, collagen, & immature chondroblasts
Interstitial growth
new cartilage forms within mass
with interstitial growth, chondrocytes retain the ability to
divide
Appostional growth
new cartilage forms at surface of pre-existing cartilage
which type of growth is more common?
Appostional growth
New chondrocytes derived from mesenchymal cells of inner perichondrium—differentiate first into
chondroblasts
More mature chondrocytes present at center of cartilage mass, with younger cells at
periphery
Cartilage is an — — —meaning most cartilage lacks blood vessels
avascular connective tissue
Exchange of metabolites occurs via
diffusion through ground substance
Limits thickness of
mature cartilage
thick cartilage contains blood vessels in
2’ cartilage canals
Cartilage contains extracellular matrix of amorphous ground substance containing
collagen
Matrix hydrated, contains ~ —, bound to proteoglycans
60-80% H2O
Accounts for its (2)
flexibility, incompressibility
GAG’s include (3)
hyaluronic acid (non-sulfated)
chondroitin sulfate
heparin sulfate
Most common glycoprotein is
chondronectin
variable types and amounts of fibers embedded within matrix produce three types of cartilage
hyaline
fibrocartilage
eastic
where is hyaline cartilage found? (6)
articular surfaces growth plates nasal septum costal cartilage (ribs) tracheal bronchial rings
hyaline cartilage is the precursor for
bone in most of skeleton
hyaline cartilage is characterized by
small aggregates of chondrocytes in amorphous matrix of ground substance, reinforced with Type II collagen fibers
fibrocartilage consists of
alternating layers of hyaline cartilage & dense connective tissue (contains Type I & Type II collagen); less cellular than either
what does fibrocartilage lack?
perichondrium
where is fibrocartilage found? (2)
intervertebral discs
some articular areas
elastic cartilage is histologically similar to
hyaline cartilage (contains Type II collagen), with addition of large #’s of elastic fibers in extracellular matrix
examples of elastic cartilage (3)
external ear
auditory & Eustacian canals
epiglottis, & larynx
examples of fibrocartilage (4)
knee
mandible [TMJ]
shoulder
sternum (ligaments, tendons, joint capsules, pubic symphysis)
Repair in cartilage is limited, because repair requires blood flow
blood flow
repair in cartilage results in
production of dense connective tissue (fibrosis)
Invasion of site by blood vessels frequently results in death of (2)
chondrocytes & formation of bone
Tendency for all hyaline cartilage to calcify with
age
Tendency for all hyaline cartilage to calcify with age, via
deposition of calcium phosphate crystals within matrix
cartilage is eventually
replaced by bone
bone is a specialized support tissue—extracellular components are
mineralized
mineralization results in (2)
rigidity & strength
two main forms of bone
woven
lamellar
Woven bone is
immature form characterized by random orientation of collagen fibers
Later remodeled into
lamellar bone
lamellar bone contains
concentric layers, called circumferential lamellae, with parallel collagen fibers
Lamellar bone can be (2)
dense & compact (e.g., cortex of long bones)
cancellous (=spongy—at ends of bones)
Cancellous bone contains network of (2)
thin, bony trabeculae (=spicules) & open spaces (marrow cavity)
Bones in limbs =
long bones
Have shaft (diaphysis) composed of — in cortex & — in medullary cavity (marrow)—
dense, compact bone
spongy, cancellous bone
bone contains (2)
red (hematopoietic) marrow or yellow (fatty) marrow
Ends of bones =
epiphyses
epiphyses are composed of
spongy, cancellous bone, covered with hyaline articular cartilage
Flared region between epiphysis & diaphysis =
metaphysis
Metaphysis contains — — of long bones (“physis” of radiologists)
epiphyseal plate
External surface of bone covered by
periosteum
periosteum
layer of fibrous connective tissue
what does periosteum contain? (2)
fibroblasts
osteoprogenitor cells
Internal marrow cavity lined by
endosteum
Sharpey’s fibers
parallel bundles of collagen fibers, extend from periosteum or Mm tendon & insert into superficial layer of bone
function of Sharpey’s fibers
provide anchorage & support
Osteoprogenitor cells
resting mesenchymal cells
where do osteoprogenitor cells reside? (2)
periosteum & endosteum
what can osteoprogenitor cells differentiate into? (2)
osteoblasts & osteocytes
Osteoblasts
roughly polygonal, mesenchymal cells derived from osteoprogenitor cells
osteoblasts are very basophilic due to synthesis of large amounts of (2)
protein & proteoglycans
Osteoblasts responsible for
synthesis of extracellular matrix & collagen
extracellular matrix & collagen is collectively referred to as
osteoid
Osteoid similar to cartilage, later mineralized to form
new bone
Osteoblasts are responsible for calcification of matrix via secretion of
matrix vesicles
Contain alkaline phosphatase, bud off osteoblasts into matrix, causing
precipitation of mineral salts (e.g., Ca & PO4)
Osteoblasts mature into osteocytes within — after matrix mineralizes
lacunae
Osteocytes
mature “bone cells”
Osteoclasts
large, multinucleate cells, probably derived from monocyte-macrophage lineage
osteoclasts are
phagocytic
osteoclasts are actively involved in (2)
resorption & remodeling of bone
osteoclasts are usually found on endosteal/ periosteal surface in depressions, called
Howship’s lacunae, or resorption bays
Osteoclasts function in Ca homeostasis by producing
organic acids & lysozymes that digest bone
Osteoclasts function in Ca homeostasis by producing organic acids & lysozymes that digest bone—secreted into ECS by
ruffled border (modified, folded plasma membrane, containing microvilli-like structures)
Bone serves as a reservoir for – & functions in
Ca
Ca homeostasis
Regulated by 2 antagonistic hormones
parathormone & calcitonin
what is parathormone secreted by?
parathyroid gland
what does parathormone stimulate?
osteoclasts activity, results in bone resorption
parathormone increases — and decreases —
increase blood ca levels
decreases renal excretion by kidneys
what is calcitonin secreted by?
thyroid gland
what does calcitonin stimulate?
osteoblast activity
what does calcitonin inhibit?
osteoclasts, results in bone deposition
what does calcitonin decrease
blood calcium levels
somatotropin stimulates
growth of epiphyseal cartilage and bone
somatotrophin decreases
blood calcium
over secretion of somatotrophin can lead to
gigantism, or acromegaly
undersecretion of somatotrophin leads to
pituitary dwarfism
Mature, compact bone composition
~ 70% inorganic salts & 30% organic matrix
> 90% of organic component is
Type I collagen
Type I collagen is synthesized by
osteoblasts
GAG’s of ground substance consist mostly of (3)
hyaluronic acid & chondroitin sulfate, as well as keratin sulfate
Non-collagenous organic molecules include (3)
osteocalcin
osteonectin
sialoproteins
osteocalcin
binds intracellular Ca during mineralization
osteonectin
bridges/ binds collagen & minerals
sialoproteins
rich in sialic acid; concentrated from plasma
Mineralized component of bone formed by inorganic salts, 1’ Ca & P, in form of
hydroxyapatite crystals–Ca10(PO4)6(OH)2
Bone also has affinity for (2)
heavy metals (e.g., Pb, Hg) & radioactive isotopes
Compact bone contains
Haversian systems, also called osteons
Osteons produced via — — —removal of existing bone by osteoclasts and redeposition of new bone by osteoblasts
bony remodeling
Size of average Haversian system ~=size of
osteoclast
Outer margin of osteon delimited by
“cement line”
Followed by invasion of
empty canal by osteoblasts