Cartilage and Bone Flashcards
What type of CT is bone/cartilage?
specialized
Connective Tissue
Primarily Structural
often the stroma of organs
includes cushioning CT found almost everywhere
cells organized in specialized ECM
classified based on ECM
Properties of Connective Tissue
Cells → mostly fibroblasts and immune cells; other specialized cells for specific function
Collagen (or collagen-based) fibers in a matrix
Matrix contains carbohydrates-based protein complexes that retain water → absorb force, maintain shape
Cell types that make collagen
- Fibroblasts
- Reticular cell
- smooth muscle cells
- epithelial cells
- equivalents
Cartilage Basics
- Avascular Tissues
- Structural Support (absorb stress)
- fibrous matrix more rigid than other CT → less rigid than bone
- water content
- proteoglycans and other glycoproteins retain water
- water has limited compressibility
- provides flexibility and resiliency, diffusion
- collagen fibers provide tensile strength
- elastic fibers allow the collagen to regain original shape
Define: Chondrocytes
Mature cells
same progenitor as fibroblasts
produce collagen and other parts of cartilage matrix → proteoglycans, multiadhesive glycoproteins
Define: Territorial Matrix
matrix around cell
stains darker
Define: Interterritorial Matrix
matrix between cells
stains lighter
Cartilage Development
From mesenchyme
progenitor cells differentiate to chondroblasts
chondroblasts produce matrix
What are the two types of cartilage growth?
Appositional
Interstitial
no exclusive (both may occur in same cartilage)
Define: Appositional Cartilage growth
new cartilage forms at the surface of existing cartilage
cartilage added from outer edges
chondroblasts in perichondrium
Define: Interstitial Cartilage Growth
new cartilage forms within existing cartilage
Cartilage Growth
- Matrix surrounds chondroblast
- fully surrounded → chondrocyte
- Newer matrix
- territorial matrix → stains darker
- Interstitial Growth
- chondroblasts in middle of cartilage divide mitotically
3 Types of Cartilage
Hyaline
Elastic
Fibrocartilage
What is found in all three types of cartilage?
chondrocytes in lacunae
Identifying Cartilage: Fibrocartilage
visible fibers; no perichondrium
associated with dense CT
Identifying Cartilage: Elastic Cartilage
elastic stain; perichondrium
similar to (and often continuous with) hyaline cartilage
Identifying Cartilage: Hyaline Cartilage
Glassy appearance; perichondrium
high proteoglycan content
Where is Hyaline Cartilage found?
fetal skeletal tissue, epiphyseal plates, articular surface, respiratory system
Major features of Hyaline Cartilage
- avascular
- surrounded by perichondrium
- high water content makes matrix glassy
Function of the Hyaline Matrix
Provides low friction, smooth surface
participates in lubricating synovial joints
distributes applied forces to the underlying bone
Components of Hyaline Matrix
collagen (mostly type II)
proteoglycan aggregates
chondrocytes
water
Ground Substance
Water and salts (primary cation is sodium)
complex carbohydrates (water retention)
proteoglycans (water retention)
Where is elastic cartilage found?
external ear
epiglottis
larynx (auditory tube)
Define: Elastic cartilage
hyaline cartilage with elastic fibers
avascular
surrounded by perichondrium
Elastic Cartilage Matrix Function
provides low friction, smooth surface
participates in lubricating synovial joints
distributes applied forces to the underlying bone
can stretch and regain original shape (less prone to breaking)
Components of Elastic Cartilage Matrix
collagen (mostly type II)
elastic fibers and lamellae
proteoglycan aggregates
chondrocytes
water
What is the difference between Elastic and Hyaline Cartilage?
presence of elastic fibers in elastic cartilage and not in Hyaline cartilage
Where is fibrocartilage found?
tendon-bone junction
intervertebral discs
menisci (knee)
etc.
Features of Fibrocartilage
fewer proteoglycans, more collagen fibers
often associated with dense regular CT
avascular
lacks a perichondrium
chondrocytes and fibroblasts surrounded by type I collagen
Function of Fibrocartilage Matrix
resistance to compression, shear stress
less likely to deform
Components of fibrocartilage matrix
collagen (type I and II)
proteoglycan aggregates
chondrocytes (isogenous rows)
fibroblasts
Water
What is the difference between fibrocartilage and dense regular CT?
Dense regular CT → cells have no lacunae
Fibrocartilage → cells have a lacunae, cells lined up
What is the structure of long bones?
- contain 3 parts:
- epiphysis
- metaphysis
- diaphysis
Define: Periosteum
fibrous CT
inner layer of osteoblasts
Define: Endosteum (osteoblasts)
marrow cavity
Define: Articular Surface
where two bones that move in apposition meet
Structural Function of Bone
protects internal organs
mechanical movements (w/ skeletal muscle)
Metabolic function of Bone
- Hematopoiesis (blood cell production in marrow)
- calcium/phosphate storage
- regulated by hormones
- amount of hormone released depends on blood calcium levels
Bone Basics: ECM: Bone Matrix
collagen and hydroxyapatite crystals (calcium phosphate)
proteoglycans and glycoproteins
growth factors
cytokines
Bone Basics: Cells
Osteoblasts → not surrounded by matrix
Osteocytes → surrounded by matrix
Osteoclasts → cleaves bone matrix to free up Ca and Phosphate
Types of Bone: Macroscopic
Compact bone
cancellous bone
Define: Compact Bone
Dense, continuous
outer layer
Define: Cancellous Bone
spongy bone
network of trabeculae
interior of bones
surrounded by marrow
Types of Bone: Microscopic
Woven
Lamellar
Define: Woven Bone
immature
developing
not as organized
Define: Lamellar Bone
Mature
visible layers
Define: Circumferential Lamellae
Goes around entire circumference of long bone
Define: Haversian Canals
run parallel to long axis
Define: Volkman’s Canals
perforating canal
connect HC
Define: Canaliculi
connect osteocytes to one another or to HC/VC
Define: Osteons
chief structural unit of compact bone
degraded and reformed in regular manner
Define: Interstitial Lamellae
remnants of old osteons
Define: Osteoprogenitor Cells
line marrow cavity
differentiate into osteoblasts
Define: Osteoblast
line marrow cavity; deposit matrix
active cells
produce collagen (I)
lay down hydroxyapatite matrix
become encased in matrix (osteocytes)
Define: Bone-lining cells
inactive osteoblasts
cover static bone
Define: osteocytes
mature bone cell; maintain matrix
encased in matrix
located in lacuna
extends processes through canaliculi
Define: Osteoclasts
phagocytic bone cell; bone resorption
large multinucleate cells
lie in howship’s lacuna on surface
degrade matrix by releasing enzyme
have small projections to absorb degraded matrix
Bone Mineralization
- increase local calcium, phosphate concentrations
- osteocalcin binds calcium
- osteoblasts secrete alkaline phosphatase, which increases local phosphate
- Secretion of vesicles that accumulate additional calcium and phosphate
- increase in local isoelectrical point crystallizes CaPO4
- Additional crystallization into hydroxyapatite crystals
initial deposit called osteoid (less mineralized) → stains more lightly than fully mineralized matrix
Two Methods of Bone Development
Intramembranous ossification
Endochondral ossification
Define: Intramembranous Ossification
similar cartilage
mesenchymal cells differentiate into osteoblasts
osteoblasts lay down matrix
Define: Endochondral Ossification
- Long bone development
- from hyaline cartilage template
- Multiple steps:
- Proliferation
- Hypertrophy
- Calcification
- Resorption
Endochondral Ossification: Proliferation
Increase number of cells
Endochondral Ossification: Hypertrophy
Increase size of cells
Endochondral Ossification: Resorption
replace cartilage and lay down bone matrix
Endochondral Ossification: Calcification
Matrix Darkens
Bone remodeling
bone is not static
- osteoclasts bore through tissue
- osteoblasts lay down new matrix (osteoid)
- lamellae reach minimum circumference
- Haversian canal is lined by bone-lining cells (endosteal cells)
What are the two types of synoviocytes in Synovial Membrane?
Phagocytic
Productive
Synovial Membrane: Synoviocytes: Phagocytic
digests debris “clean up” in synovial fluid
Synovial Membrane: Synoviocytes: Productive
makes synovial fluid
Contents of synovial fluid
hyaluronan → important for cushioning
lubricin
nutrients (including oxygen)
Function of Synovial Fluid
cushioning impact
lubrication of the articular cartilage
support of the articular cartilage
Bone Breaks
- bone breaks
- blood clot forms
- soft callus formation → granulation tissue and fibrocartilage form
- sponge bone fills
- bone remodeling → new compact bone
Blast vs. Cyte
Blast Builds
Cyte is Surrounded (Cyte sits)
Clasts cleave
Blast v. Cyte: Chondroblast/Osteoblast
lay down new matrix
build up tissue
Blast v. Cyte: Chondrocyte/Osteocyte
maintain tissue
surrounded by matrix
Both cartilage and bone have cells in…
lacuna
Cartilage is support without…
rigidity
collagen fibers in substantial water-based solid matrix
Bone is more __ that cartilage, but still has some flexibility
rigid
bone ___ constantly, and can heal from __. Cartilage is __ in both respects.
bone remodels constantly, and can heal from breaks. Cartilage is limited in both respects.
