SKELETAL TISSUE Flashcards
what does the skeletal system include?
bones of skeleton cartilage ligaments tendons CT
what is the function of skeletal system?
Structural support
Levers:change direction of forces generated by skeletal muscle
protection, storage, blood cell production
what is cartilage?
supporting CT
what does cartilage contain?
gelatinous matrix: ground substance and fibres
what are cartilage cells?
chondrocytes occupy lacunae
what are the characteristic of cartilage?
Poorly vascularised
Exchange nutrients/waste occurs by diffusion
heals slowly
what is cartilage derived from?
embryonic mesoderm
what is mesoderm made of?
mesenchyme
how is cartilage separated from surrounding tissue?
by perichondrium
how many layers does perichondrium have?
2 layers
Outer fibrous irregular CT layer
Inner cellular layer
what are the 3 types of cartilage?
hyaline, elastic, fibrocartilage
what does hyaline cartilage contain?
translucent matrix
covered by dense perichondrium
what does the matrix contain?
closely packed collagen fibres
what does the matrix provide?
Provides tough but flexible support
give examples of hyaline cartilage
Connect ribs & sternum
Nasal cartilages & resp tract
what is articular cartilage?
cover opposing bone surfaces joints e.g. knee & elbow
what is elastic cartilage?
Contains many elastic fibres: resilient & flexible
Tolerates distortion - returns back to shape
give examples of elastic cartilage?
External flap outer ear, epiglottis, larynx
what does fibrocartilage contain?
little ground substance
matrix dominated by large collagen fibres which are densely interwoven
what is a characteristic of fibrocartilage?
Tough & durable:
resists compression
absorbs shocks
prevents damaging bone to bone contact
give examples of fibrocartilage
Pads between spinal vertebrae
Between pubic bones in pelvis
Around/within some joints & tendons
what are the 2 mechanism of cartilage growth?
interstitial
appositional
what happens in interstitial growth?
Chondrocytes: undergo cell division -additional matrix
Enlarges cartilage from within
what is interstitial growth important in?
Important during embryonic development
what happens in appositional growth?
New layers added to surface
Inner layer of perichondrium divides
what happens to cells in appositional growth?
cells - immature chondrocytes - cartilage matrix - differentiate mature chondrocytes
what is the source of new cartilage cells?
fibroblasts
why is appositional growth important?
increases size of cartilage by adding to outer surface
what is the role of hyaline cartilage in growing bone?
Initial skeleton of foetus
Each cartilage is miniature bone model
what is the precursor of bone developed by?
endochrondral ossification
what is osteogenesis?
Bone formation & growth
when does osteogenesis take place?
begins 6 wks after fertilisation, continues through fertilisation
what is ossification?
replacement of cartilage & CT by bone
what are the 2 forms of ossification?
Endochondral
Intramembranous
what is endochondral ossification?
Bone replaces existing cartilage
6 wk embryo cartilaginous models of limb bone replaced by bone
what happens in endochondral ossification?
Begins near middle of shaft 1o centre of ossification
Centre of epiphyses (head) calcify: 2o ossification centre
Epiphyses: filled with spongy bone
what bones are affected by endochondral ossification?
extremities & axial weight bearing
e.g. Femur, vertebrae
what is intramembranous ossification?
Bone develops from mesenchyme / CT
Stem cells within connective tissue differentiate osteoblasts
what happens in intramembranous ossification?
Mesenchymal cells cluster & secrete matrix
Calcification occurs mesenchymal cells osteoblasts
Ossification begins = Ossification Centre
1st forms spongy bone: remodelling:
compact bone
what bones are affected by intramembranous ossification?
flat bones: skull, mandible, clavicle
what are the components of bone?
supporting CT, specialised cells, extracellular fibres, ground substance, calcium phosphate, collagen fibres, cells
how is blood supplied to bone?
Nutrient artery
Metaphyseal vessels
Periosteal vessels
what are long bones?
long & slender
give examples of long bone
thigh (femur)
arm (humerous)
what are short bones?
small & boxy
give examples of short bone
carpals (wrist)
tarsals (ankles)
what are flat bones?
thin & parallel surfaces
give examples of flat bones
parietal, ribs & scapula
what are irregular bones?
complex, notched/ridged surfaces
give examples of irregular bones
vertebrae, pelvis
what are sesamoid bones?
Small & flat
give examples of sesamoid bones
develop inside tendons near joints eg kneecap
what are sutural bones?
Small, flat / irregular
give examples of sutural bones
Between flat bones of skull
what does a long bone contain?
Central shaft (diaphysis) Expanded ends (epiphyses) Central: marrow cavity epiphyses of adjacent bones - articulate & covered by articular cartilage: hyaline
what are compact/dense bones?
relatively solid
located on surface of bone
forms diaphysis
what is spongy/cancellous bone?
forms open network
interior of bone
forms epiphysis
what does the outer surface periosteum contain?
Fibrous outer layer & cellular inner layer
what are osteocytes?
mature bone cells cannot divide, occupy a lacuna
what is a lacuna?
pocket / layers of matrix = Lamellae
what is a canuliculi?
passageways – link osteocytes
what is the function of osteocytes?
maintain normal function by recycling Ca2+ salts
repair damaged bone
released from lacunae- less specialised cell type
what are osteoblasts?
precursor cells
production of new bone: osteogenesis
what is the function of osteoblasts?
make & release proteins / organic components of matrix
increase local conc of Ca2+ phosphate
what do osteoblasts form?
Form osteocytes / develop from osteoblasts- surrounded by bone matrix
what are osteoprogenitor cells?
mesenchymal cells =
stem cells which divide daughter cells -osteoblasts
what do osteoprogenitor cells do?
maintain populations of osteoblasts
what are osteoclasts?
giant cells
remove bone matrix
derived from monocytes
what do osteoclasts do?
Secrete acids & proteolytic enzymes dissolve bone matrix:
osteolysis
what is the importance of osteoclasts?
regulation of Ca2+ & phosphate conc of body
what is the functional unit in compact bone?
osteon / Haversian system
how are osteocytes arranged in compact bone?
in concentric layers around central canal with blood vessels
how are the lamellae arranged in compact bone?
form cylinders around central canal
what are the perforating canals?
passageways
Blood vessels in canals supply blood to osteons
what is compact bone surrounded by?
periosteum
how is lamellae arranged in spongy bone?
form rods - trabeculae
how is an open network created in spongy bone?
Frequent branching thin trabeculae
what are the characteristics of spongy bone?
No capillaries or venules
Nutrients reach by diffusion along -
cannuliculi
red marrow found between trabeculae
what is the structure of compact bone?
stresses come from limited range of directions
osteons aligned in same way
what is the structure of spongy bone?
bones not heavily stressed / stresses arrive in many directions
lighter than compact
what is the effect of aging on bones?
become thinner & weaker =osteopenia
what is the effect of reduction in bone mass?
Osteoblast activity decreases
what is osteoporosis?
Function of bone compromised
what else is important in bone maintenance?
hormones
