Histology: Bone and Cartilage Flashcards
Cartilage origin
Mesenchyme
Cartilage considered _____ tissue
Considered specialized CT due to supportive properties
What is this tissue?
Hyaline Cartilage - shown w/ perichondrium
Label
Blue - osteoid
Red cells - osteoblasts
isolated cells - osteocytes
Differences between Bone and Cartilage
Bone matrix can become mineralized. If cartilage matrix mineralizes it will degenerate
Cartilage is avascular, bone is highly vascular
Cartilage lacks nerve innervation
Cartilage growth is appositional and interstitial; bone grows only appositionally
Cartilage cell types
chondroblasts – active
chondrocytes – considered to be inactive
Cell morphology (Cartilage)
lacunae
few mitochondria – predominantly anaerobic
typical Golgi, RER
Cartilage matrix is 60-80% _______
Water
Cartilage matrix contains
Ground substance and fibers
Cartilage ground substance contains
proteoglycan (aggrecan - hyaluronate - extremely hydrophilic, binds water to create stiff gel) and glycoproteins (chondronectin - help bind various components of cartilage)
Cartilage matrix fibers
Collagen (+elastin for elastic cartilage)
Microfibrillar
Difficult to see d/t same refractive index as ground substance
Cartilage matrix is _________ (blood/lymph)
Avascular
Cartilage types
Hyaline cartilage
Elastic
Fibrocartilage
Most common cartilage
Hyaline
Hyaline cartilage locations
Fetal skeleton, epiphyseal plate in children
nose, larynx, trachea, ribs articular cartilage in adult
Morphology of Hyaline Cartilage
glossy, collagenous fibers (Type ____) difficult to see
______ with 2 or more chondrocytes = ________
outer layer = ___________
glossy, collagenous fibers (Type II) difficult to see
lacunae with 2 or more chondrocytes = isogenous group
perichondrium
Perichondrium of hyaline cartilage (fibrous layer, chondrogenic zone, function, articular cartilage)
fibrous layer – contains fibroblasts and type I collagen
chondrogenic zone – contains chondroblasts
function
protection
continuous supply of chondrocytes
lacking on articular surface of articular cartilage
Hyaline cartilage nutrition
diffusion – matrix is permeable to nutrients, oxygen and metabolic waste
mineralization prevents diffusion
Growth of hyaline cartilage (appositional, interstitial, regeneration)
appositional – addition of chondroblasts onto surface
interstitial – mitotic activity of chondroblasts (formation of isogenous nests) and synthesis of matrix - note: not possible in bone
regeneration of damaged cartilage is difficult
Elastic cartilage location
pinna of ear, eustachian tube, external auditory canal
epiglottis, some laryngeal cartilages
Elastic Cartilage morphology
abundance of ______ fibers
______ fibers and ground substance also present
higher density of _________ than hyaline
_______________ (outer layer)
abundance of elastic fibers
collagen (Type II) and ground substance also present
higher density of cells/isogenous nests than hyaline
perichondrium
Nutrition of elastic cartilage
Same as hyaline cartilage (diffusion)
Fibrocartilage Locations
Intervertebral discs, pubic symphysis, tendon/ligament attachments
Fibrocartilage morphology:
large ______ fibers (____)
_______ in ground substance
_____ cells per unit area
Perichondrium?
large collagenous fibers (Type I)
reduction in ground substance
fewer cells per unit area
no perichondrium
Herniated intervertebral disc
Rupture of annulus fibrosis allowing expulsion of nucleus pulposus
Dislocation of annulus and compression of spinal cord
Fibrocartilage
General Characteristics of Bone
Dynamic - living tissue, Undergoes continuous remodeling, repair
Structural support
Calcium reservoir
Bones contains ____% of body calcium and for what purpose
99%
Mineral metastasis
3 bone cell types
osteoblasts, osteocytes, osteoclasts
Bone matrix contains
Ground substance, type I collagen, minerals (ca, MN, FE, SR)
Bone is _____ vascular/innervated (vs cartilage)
Bone is HIGHLY innervated/vascular - cartilage is not
Osteoblast function
synthesis of organic matrix = osteoid prior to mineralization
deposition of inorganic components
alkaline phosphatase secretion → concentrate phosphate ions → organic matrix (calcium added)
Osteoblast location and appearance
Bone surface
cuboidal to columnar when active
basophilic
Cell process of osteoblasts
in contact with neighboring osteoblasts
Osteoblasts have receptors for ____
receptors for parathyroid hormone: binding of parathyroid hormone causes release of osteoclast stimulating factor from the osteoblast
Osteoblasts –>
Osteocytes (completely surrounded by matrix)
Osteocytes have ______ protein synthesis (compared to osteoblasts)
Reduced
Function of osteocytes
maintenance of matrix and regulation of calcium; death of osteocyte → resorption of the matrix
Osteocytes are located in __________
lacunae
Osteocyte cell processes
canaliculi = channels through matrix for osteocyte processes
Used to be “arms” of osteoblasts - now canaliculi
Osteocyte communicationn
communicate via gap junctions
cell-cell coordination
nutrient transfer
Describe and function
Sharpey’s fibers: anchor periosteum to bone
What are black dots?
Osteocytes - cells that are alive, communicated via caniculi/gap junctions
label zones of epiphyseal plate
Resting
Proliferative
Hypertrophic
Calcified Cartilage
Ossification
Large multinucleated motile bone cells
osteoclasts
Osteoclasts are responsible for
bone resorption
Osteoclasts are derived from ______ and amitotic/mitotic
derived from circulating monocytes (not “related” to osteoblasts/osteocytes)
amitotic
Osteoclast ruffled border and process
“Ruffled border” - where osteoclast lies against bony surface
Membranes pump H+ into sub-osteoclastic compartment
Lower pH and mineral is liberated
Minerals enter osteoclast and are then delivered to nearby capillaries
Osteoclast secretes lysosomal hydrolases, collagenase, and gelatinase into sub-osteoclastic compartment
Degrade organic components of decalcified bone matrix
Degradation products are endocytosed by osteoclast
Broken down into amino acids, monosaccharides, and disaccharides and released into capillaries
Howship’s Lacunae
regions of resorbed matrix containing an osteoclast - looks like a depression in surface of bone w/ osteoclast
Bone matrix composition
Inorganic (mostly calcium) and organic (type 1 collagen and ground substance)
Organic part of bone matrix
type I collagen
ground substance
chondroitin sulfate form proteoglycan
hyaluronate aggregates
glycoproteins: osteonectin; osteocalcin; osteopontin → bind everything to everything else
Types of bone
Cancellous, compact
primary, secondary
Cancellous bone
spicules or trabeculae of bone united to form network
found in interior of bone (e.g. idploe of skull, ends of long bones)
Compact bone
found on bone exteriors
dense, thick layers
Primary bone
first bone tissue to appear during growth or repair
woven bone
irregular array of collagen fibers
Secondary bone
replaces primary bone
parallel arrays of collagen
lamellar deposition of matrix
production of Haversian systems
Diaphysis of long bone
bone shaft between opposing epiphyseal plates
primarily compact bone, but metaphysis is cancellous (spongy)
periosteum
endosteum
marrow cavity
Metaphysis of long bone
distal end of diaphysis
cancellous/spongy
Epiphysis of long bone
distal end of long bone
articular hyaline cartilage cap (no perichondrium - just adjacent to synovial fluid)
medullary cavity is cancellous with marrow cavity
Epiphyseal plate of long bone
junction between diaphysis and epiphysis
hyaline cartilage in a child
perichondrium continuous with periosteum
Responsible for bone growth
Periosteum of compact bone
fibrous layer
-fibroblasts, collagen, elastin, protection of bone
Osteogenic layer (can’t normally see, unless fracture/growing)
- Osteoblasts adjacent to bone surface, Osteoclasts if remodeling is underway, Osteoprogenitor cells – precursors to osteoblasts
Blood vessels, nerves
Sharpey’s fibers: anchor periosteum to bone
endosteum of compact bone
between bone marrow and bone matrix
layer of osteoblasts, osteoclasts and few osteogenic cells
Haversian System (Osteon)
concentric lamellae of bone
usually don’t exceed 10/osteon
canaliculi (little processes) of osteocytes
plane of collagen deposition perpendicular to adjacent lamellae - strength
surround vascular passageways running longitudinally
blood vessels, nerves, lymphatics
Volkmann’s Canals
vascular passageways running radially
not surrounded by bone lamellae
blood vessels, nerves, lymphatics → Haversian canals or bone marrow cavity
Interstitial Lamellae of compact bone
remnants of partly resorbed osteons (incomplete osteons visible between complete osteons)
no vessels
Outer Circumfrential Lamellae of compact bone
beneath periosteum
usually do not completely encircle bone shaft
Inner circumfrential lamellae of compact bone
adjacent to endosteum
incomplete
Bone development: _______ growth only
Appositional Growth Only (cannot grow by interstitial growth - mineralized)
osteocytes are amitotic
calcified matrix cannot expand - deposit onto already existing bone
Types of bone development
intramembranous, endochondral ossification
Note: both types of ossification result in compact and cancellous bone tissue formation
Intramembranous ossification
embryonic CT precursor
CT template is vascular
gives rise to “membrane” bones = Skull, mandible, maxilla, clavicles
Endochondral ossification
hyaline cartilage precursor/template
cartilage is avascular
calcified cartilage matrix is removed
Intramembranous ossification: Primary Ossifcation center, Mineralization of Matrix, Spicule Formation, Cancellous and compact bone
differentiation of mesenchymal cells into osteoblasts, osteoid secretion
encapsulation of osteoblasts –> osteocytes, immature woven bone, mature lamellar bone
small mineralized “fingers” of bone, surrounded by osteoblasts, fusion of adjacent spicules –> trabeculae
depends on degree of lamellar bone deposition and spacing of spicule and trabeculae
Endochondral ossification: bone collar formation
intramembranous ossification around diaphysis of cartilage template
prevents diffusion into cartilage matrix
calcification of cartilage matrix
hypertrophy and destruction of chondrocytes
resorption of matrix surrounding chondrocytes
Endochondral ossification: Primary Ossification Center
osteogenic bud invasion
penetration of calcified cartilage by capillaries
introduction of osteoprogenitor cells
differentiation of osteoprogenitors into osteoblasts
deposition of bone matrix on remnants of cartilage matrix
first appearance of bone marrow precursors
osteoclast resorption of cartilage matrix and remodeling of bone spicules, formation of medullary cavity
expansion of bone collar
further calcification of cartilage
longitudinal expansion of bone deposition
Endochondral Ossification: Secondary OC
ossification of epiphysis
no bone collar formation
bone growth is radial
articular cartilage remains
epiphyseal cartilage continues appositional and interstitial growth
Ossification of Epiphyseal cartilage
Five zones based on chondrocyte disposition
Closure of epiphyseal plate in young adult
5 zones based on chondrocyte diposition
resting – normal hyaline cartilage
proliferative – high mitotic activity, columns of isogenous nests formed (stack of pancakes)
hypertrophic – glycogen accumulation, very little matrix
calcified – death of chondrocytes, deposition of hydroxyapatite + calcification
ossification – osteoblasts and bone matrix appear
Synovial Joint
Synovial membrane, matrix, blood and lymphatic vessels
Synovial membrane
Fibroblasts (type B cells) - secrete synovial fluid, hyaluronate and GAGs - viscosity, hydrophilic, lubrication of joint, provides nutrients for articular cartilage
macrophages (type A cells)
not an epithelium (epithelioid-like though)
Synovial joint matrix
collagen
ground substance
adipose cells
Bone plasticity
stress induced remodeling (i.e. braces)
fracture
disuse
hormone changes, developmental and pathological
Bone- calcium homeostasis, 2 hormones
99% of body calcium is in bone
Parathyroid hormone – increases Ca resorption
stimulates osteoclast activity (via binding to parathyroid hormone receptors on osteoblasts) and osteoclast numbers
resorption of matrix
Calcitonin – promotes calcium deposition
inhibits osteoclast activity
matrix deposition
Produced by Thyroid gland
Scurvy
vitamin C deficiency
improper collagen synthesis (hydroxyproline)
weakness in epiphyseal plate, diaphysis
loosening of teeth
Rickets
calcium deficiency in children
Incomplete bone matrix calcification
spicules distort under strain → bone deformation
Osteomalacia
calcium deficiency in adults
deficient calcification of new bone
decalcification of existing bone
no bone distortion
Osteoporosis
Most common in postmenopausal women
Bone tissue diminished – due to a more rapid destruction of bone by osteoclasts than osteoblast formation of bone
Estrogen therapy helps alleviate this tendency but has many side effects (cancer, heart attacks), bisphosphonates more common now
