Chapter 5-Skeletal System Flashcards
2 types of bone tissue
- compact(dense smooth bone)
- spongy(bone with open spaces within)
Components of Skeletal system
- cartilage
- bone
- tendons
- ligaments
functions of skeletal system
- protection
- support (rigid structure)
- movement (bones as levers)
- storage (ca, P, fat)
- blood cell protection
cartilage consists of
-cells
extracellular matrix
cells in cartilage
chondrocytes found in compartments called lacunae
extracellular matrix
- collagen/elastic fibers
- ground substance of chondrotin sulfates
types of cartilage
hyaline
elastic
fibrocartilage
why does cartilage heal slowly?
no arteries, veins or lymphocytes
hyaline cartilage
- most common
- made up of chondrocytes, chondrotin sulfate, some collagen
location of hyaline cartilage
embryonic skeleton, articular surfaces, respiratory passages, nasal septum, between ribs and sternum
elastic cartilage
- flexible
- structure: chondrocytes, chondrotin sulfate, densely packed elastic fibers
- location: auricle, tip and lateral walls of nose, epiglottis
fibrocartilage
- very strong
- structure: chondrocytes, chondrotin sulfate, densely packed collagen fibers
- location: intervertebral disc, public symphysis, articular cartilage in knee
perichondrium
- fibrous connective tissue
- surrounds cartilage
- provides support and protection; new chondrocytes
perichondrium location
hyaline cartilage and elastic cartilage
absent form perichondrium
articular surfaces and fibrocartilage
layers of perichondrium
- outer: binds cartilage to adjacent tissues; provides support and protection
- inner: for growth and maintenance
apposition growth
- starts in perichondrium
- mesenchymal cells at periphery form in inner layer of perichondrium
- mesenchyme move towards matrix to become chondrogenic cells
how are chondrocytes formed from apposition growth
- chondrogenic cells aggregate and become chondroblasts
- chondroblasts secrete matrix-force cells apart
- chondroblasts become enclosed in matrix and become chondrocytes
interstitial growth
- chondrocytes enclosed in matrix and divide
- as the move apart, matrix forms between them
- growth of cartilage from within
osseous tissue
- supportive CT
- contains specialized cells
- solid extracellular matrix
- –osteoid (organic portion, protein fibers)
- –ground substance (Ca salts)
- –water
osteoprogenitor
- bone cell
- mesenchymal cells
- predecessor to osteroblasts
- play role in initial growth and fracture repair
osteoblasts
- derived from osteogenic cells
- secrete osteoid
- common in growing bone
- predecessor to osteocytes
- more osteoblasts=stronger bone
osteocytes
- mature cells
- exist within bone matrix
- maintain Ca and PO4 homeostasis
- found in spaces called lacunae
osteoclasts
- involved in osteolysis (bone break down)
- increase osteoclast activity=weaker bone
- very large
- formed from fusion of many white blood stem cells
bone matrix is composed of…
Inorganic material -65% -brittle salts --mostly hydroxyapatite Osteoid -orgaic -35% -flexible fibers (collagen, glycoproteins, proteoglycans
2 types of bone
compact bone
-arranged in osteons
spongy bone
-arranged in trabeculae
compact bone osteocytes communicate how?
osteocytes
-osteocytes communicate through canaliculi that radiate outward and connect one cell to the next cell
osteons
a unit of compact bone
- concentric lamellae of matrix surrounding acentral canal
- contains blood vessels and nerves
how are osteons connected to each other
perforating canals
3 types of lamellae
-concentric
interstitial
circumferential
concentric lamellae
- layers of bone surrounding the central canal
- make up osteons
interstitial lamellae
- found between osteons
- represents older osteons partially removed during tissue remodeling
circumferential lamellae
surround the compact bone
-directly produced from periosteum
spongy bone contains
trabeculae
- osteocytes in lacunae
- canaliculi
- matrix
spongy bone does not contain
- osteons
- central canal
trabeculae
- latticework of thin plates of bone oriented along lines of stress
- spaces are filled with red marrow where blood cells develop
- found in ends of long bones and inside flat bones
- lightens the bones, allows for movement
periosteum
- encloses bone
- absent at site of attachment of muscles, tendons and ligaments; surfaces covered by articular cartilage
layers of periosteum
outer fibrous: gives rise to collage
Inner: for growth or new cells and maintenance
endosteum
- 1 cell layer
- covers surfaces of spongy bone and medullary cavity
cell types of endosteum
osteogenic
osteoblasts
osteoclasts
anatomy of a long bone
diaphysis: shaft
epiphysis: one end of long bone
metaphysis: growth plate region
articular cartilage: over joint surface; acts as friction and shock absorber
medullary cavity: marrow cavity
2 types of bone marrow
- yellow marrow
- red marrow
yellow marrow
- areolar and adipose CT
- in medullary cavity of long bones
- energy storage
- absent in infants
red marrow
- areolar and myeloid (precursor to red blood cells) tissue
- produces all types of blood cells
location of red marrow
- medullary cavities of infants
- spongy bones in adults
blood and nerve supply of bone
- periosteal arteries: supply periosteum
- nutrient arteries
- -enter through nutrient foramen, supplies compact bone of diaphysis and yellow marrow
- metaphyseal and epipheyseal arteris
- -supply red marrow ad bone tissue of epiphysis and metaphyses
how does bone growth occur
ossification (replacing CT with bone)
2 types of ossification
intramembranous
-mesenchymal cells->spongy bone
endochondral
-hyaline cartilage->spongy bone
intramembranous ossification begins when and forms what
about 8 week in embryo -mainly finished by week 15 Forms: -cranial flat bones -facial bones -dentary bones -clavicle -sesmoid bones
primary ossification center
- intramembranous oss.
- location where bone growth begins
where does bone growth begin plus beginning steps
primary ossification center
- mesenchymal cells arrange around BVs
- bone morphogenic proteins release
- mesenchymal cells divide and become osteoblasts
what do osteoblasts do after formation
- secrete osteoid
- become isolated->osteocytes
- produce spicules of bone that interconnect
how does spongy bone form during intramembranous ossification
- mesenchymal cells at surface form inner layer of periosteum
- calcified matrix is degraded by osteoclasts to form spongy bone
- end up with spongy bone covered in thin layer of compact bone
when does endochondral ossification begin and what forms
-bone relaces cartilage model
-begins at week 7 of embryo
-continues to adulthood
Forms:
-long bones
-most short bones
-non-cranial irregular and flat bones
-middle ear ossicles
step 1 of endochondral ossification
- hyaline cartilage forms model of future bone
- cartilage enlarges; chondrocytes near center hypertrophy
- -matrix reduced to struts
- -chondrocytes deprived of nutrients and die
step 2 of E.O.
BV’s grow around and penetrate cartilage
- cells differentiate into osteoblasts
- compact bone forms around diaphysis
step 3 of E.O.
- spongy bone forms in center of model
- -primary ossification center (creates diaphysis)
- nutrient artery in spongy bone forms and penetrates
step 4 of E.O.
remodeling of the shaft
- formation of the medullary cavity
- length increases
step 5 of E.O
- BV’s penetrate ends of model
- secondary ossification centers form at both epiphyses (created here)
step 6 of E.O.
- ends with incomplete ossification of epiphysis
- some cartilage remains
- -articular cartilage
- -epiphyseal plate (growth plate)
bone growth: elongation
-occurs at epiphyseal plate
growth in length continues until 2 ossification centers meet
-relative thickness of epiphyseal plat does not change until growth almost complete; then:
–cartilage depleted and epiphyseal plate narrows to epiphyseal line
bone growth: appositional
- compact bone deposited beneath periosteum
- bone thickens
- bone remodeling occurs throughout life
- -due to osteoclasts and osteoblasts
bone remodeling
- ongoing since osteoclasts carve out small tunnels and osteoblasts rebuild osteons
- continual redistribution of bone matrix along lines of mechanical stress
- 4% of compact bone, 20% of spongy bone remodeled per year
- distal femur fully remodeled every 4 months
fractures: break in a bone (types)
closed (simple): break that does not penetrate skin
open (compound): broken bone penetrates through skin
bone repair
-fractures treated by reduction and immobilization
stages of bone repair
- fracture hematoma
- fibrocartilage callus
- bony callus
- remodel tissue
fracture hematoma formation
- facture hematoma forms within hours of injury
- mass of blood
- swelling and inflammation occur in response to dead bone cells
- phagocytes and osteoclasts eliminate dead cells/broken matrix
fibrocartilaginous callus formation
- consists of mass bridging broken ends of bone
- fibroblasts in periosteum produce collagen
- periosteum cells differentiate into chondrocytes
- results in fibrocartilage
- about 3 weeks
bony callus formation
- endochondral ossification
- formation of bony callus occurs as fibrocartilaginous callus is converted to spongy bone trabeculae
- bony callus lasts 3-4 months
bone remodeling
- remaining dead bone fragments are resorbed, compact bone replaces spongy bone
- well-healed fracture is virtually undetectable
- process can take weeks to months depending on severity
factors affecting growth, repair, development
- nutrition=vitamin D
- sunlight (vit D)
- hormones: PTH, calcitonin, GH, thyroid hormone, sex hormones
- physical stress
osteoporosis
- abnormal reduction of bone mass
- reasons:
- loss of estrogen at menopause
- deficiency of minerals in youth
- imbalance in activity between osteoblasts and osteoclasts
fibrodysplasia ossificans progressiva
- CTP gets ossified when injured
- genetic
- injury results in inappropriate bone formation
- early adulthood: freezing of joints
- early 20s: confined to wheelchair
- starvation and pneumonia result
- no treatment
