Cartilage and Bone Tissue Flashcards
1
Q
Where is cartilage found in the body?
A
- articular joints of bones
- organs such as trachea and bronchi
- costal cartilage connecting ribs to sternum
- in the larynx
- in the growth plate of long bones
- in the nose, ears, epiglottis, and Eustachian tubes
2
Q
What are the properties of cartilage?
A
- connective tissue from mesenchymal stem cells
- tough and resilient, cushions joints
- contains 60-80% water
- covered w/ dense perichondrium (helps resist outer cartilage expansion when compressed, contains the stem cells)
- no nerves or blood vessels (nutrients/gases travel from BV’s of surrounding tissue by diffusion)
- difficult to repair if damaged
3
Q
What are the different types of cells found within cartilage?
A
- chondroblast: forms (builds) initial cartilage matrix and are located next to perichondrium; have mitotic capabilities; precursor of chondrocytes
- chondrocyte: mature cells embedded within the cartilage extracellular matrix in a space referred to as a cartilage lacuna; can proliferate to form clusters call isogenous groups (pictured in the other side of the flash card)
4
Q
What is the cartilage extracellular matrix composed of?
What are the fibers present?
A
- composition: hyaluronic acid, proteoglycans, and water
- fibers: type-II collagen, some have added elastin or type-I collagen
5
Q
- layer of dense irregular CT covering hyaline and elastic cartilage
- lacking in fibrocartilage and articular cartilage (a subtype of hyaline)
- essential for growth and maintenance of cartilage
- two layers: outer/fibrous layer and inner/chondrogenic layer
A
perichondrium
6
Q
What is the inner and outer layer of perichondrium composed of?
A
- inner/fibrous layer: type-I collagen and fibroblasts
- outer/chondrogenic layer: adjacent to cartilage ECM, contains mesenchymal stem cells for source of chondroblasts that divide/differentiate into chondrocytes
7
Q
- most abundant type of cartilage
- has a glassy, shiny, smooth surface
- plays key role in bone development and growth
- location: joint surfaces, costal cartilage, larynx, trachea, bronchi, and nose
- cartilage ECM cells secretes contain type-II collagen and proteoglycans (chondroitin sulfate, keratan sulfate, and hyaluronic acid) that all bind to H20 (well hydrated matrix)
- surrounded by perichondrium (except on articular surfaces)
- surrounded by synovial fluid in moveable joints = glides easily
- chondrocytes located within lacunae or isogenous groups: territorial matrix (immediately surround chondrocytes, type-II collagen random and high proteoglycans) and interterritorial matrix (surrounds territorial, contains more type-II collagen and less proteoglycans)
- TLDR: great shock absorbing properties, covers ends of adjoining bones in moveable joints
A
hyaline cartilage
8
Q
- type of cartilage
- contains abundant network of elastic fibers embedded in type-II collagen (w/ staining, elastic fibers appear as dark bundles throughout matrix)
- elastic fibers allow for flexible recoil/rebound = retains shape after deformation
- perichondrium is present
- locations: auricle of ear, walls of external auditory canals, auditory (Eustachian) tubes, epiglottis
A
elastic cartilage
9
Q
- type of cartilage that is a mix of hyaline cartilage and dense CT
- lacks perichondrium
- tough, resists tension, yet cushioning support tissue for bone
- locations: intervertebral discs, pubic symphysis, and some menisci of long bone joints
- chondrocytes typically arranged in single rows of isogenous aggregates
- sparse matrix of type-II collagen, w/ fibroblasts and dense bundles of type-I collagen (fibers oriented in the direction of functional stress and provides extra tensile strength)
A
fibrocartilage
10
Q
- type of cartilage
- found on surfaces of moveable joints (2-5 mm thick)
- comparable to hyaline cartilage (remnant of originial hyaline cartilage template used by the developing bone)
- no perichondrium present
- collagen fibers run perpendicular to the tissue surface, but bend gradually to form an arc
- establishes four zones
A
articular cartilage
11
Q
Briefly describe appositional growth as it relates to cartilage:
A
(chondroblasts adjacent to the perichondrium form new cartilage on the surface)
- perichondrial mesenchymal cells differentiate into chondroblasts
- chondroblasts secrete ECM and become surrounded to form chondrocytes
- process continues to keep adding layers of cartilage on top of previous layer
12
Q
Briefly describe interstitial growth as it relates to cartilage:
A
(growth expands within cartilage)
- chondrocytes within cartilage divide forming clusters of cells called isogenous groups
- they then deposit extracellular matrix, spreading themselves from one another thereby expanding cartilage from within the cartilage, creating territorial matrix
- territorial matrix: newly synthesized ECM adjacent chondrocytes, stains differently
13
Q
Describe the repair of cartilage:
A
- cartilage undergoes very slow, incomplete repair
- more efficient in young children
- poor capacity for repair due to its avascularity and low metabolic rate
- cells from the perichondrium invade damaged area and produce new cartilage or dense CT, may even replace it w/ bone
14
Q
What are the functions of bone?
A
- support: provides structural framework
- movement: acts as levers for skeletal muscles
- protection: of organs
- mineral storage: reservoir for minerals including 99% of body’s calcium
- blood-cell formation: protected space for red marrow
15
Q
- type of bone cell
- mesenchymal cells that produce osteoblasts (found in periosteum and endosteum)
A
osteoprogenitor cells
16
Q
- type of bone cell
- produce osteoid, non-mineralized organic matrix, then initiate and control mineralization of osteoid (organic matrix: type-I collagen and proteoglycans; inorganic matrix: calcium and hydroxyapatite crystals (mineral salts) between fibers)
- produced from mesenchymal stem cells, when active are cuboidal mononuclear cells
- fates: osteocytes embedded in bone, bone lining cell on surface, die by apoptosis
A
osteoblasts
17
Q
- type of bone cell
- mature osteoblasts trapped in bone matrix, located in space called lacuna
- cell processes extend in canaliculi (tiny canals within matrix): communicate w/ other cells by gap junctions, receive nutrient flow via canaliculi
- maintain bone health: mechanosensory cells, control activity of osteoblasts and osteoclasts
A
osteocytes
18
Q
- type of bone cell
- differentiate from monocytic cells (macrophage-like from the blood)
- multinucleated (labeled O): located on bone surfaces, create Howship’s lacunae (labeled H)
- remove bone tissue (bone resorption) by degrading the matrix: secreting acids and proteases
- fate: eventually apoptosis
- important endocrine target for regulating calcium levels
A
osteoclasts
19
Q
What is the overall structure of long bones?
A
- epiphysis: knobby regions at ends of bones, compact bone is superficial w/ trabecular bone deep to surface, contains epiphyseal plate
- diaphysis: elongated shaft
- metaphysis: between diaphysis and epiphysis, consists of spongy bone
- epiphyseal line: within metaphysis, epiphyseal plate has fused
- marrow (meduallary) cavity: cylindrical space in diaphysis containing bone marrow
- articular cartilage: cap of hyaline cartilage found at ends of bones articulating w/ other bones
- primary/secondary osteogenic centers: sites of osteogenesis within cartilage of developing long bones
20
Q
What are the 2 bone coverings?
A
- periosteum: dense irregular CT covering external surface, does not cover articular cartilages, neurovascular, anchored by perforating fibers embedded in bone matrix, contains osteoblasts and osteoblast precursors
- endosteum: CT lining of all trabeculae and marrow cavity; contains osteoprogenitor cells, reticular cells of bone marrow, and CT fibers
21
Q
What are the 2 different types of bone?
A
- compact (cortical) bone: forms outer walls of bones, primary structure (lamellar (layers) either as circumferential arrangement (osteon) or partial rings (interstitial lamellae))
- trabecular (cancellous or spongy) bone: forms network of bony plates or rods surrounded by marrow, no osteons, proximal/distal ends of long bones, can be woven or lamellar bone
22
Q
What is the organization of the osteon (Haversian system)?
A
- osteon: cylindrical/layered structures comprising mature compact bone, run parallel to diaphysis, consists of concentric lamellae (bone matrix surrounding a central canal), has osteonal canal w/ blood vessels/nerves
- concentric lamellae (layered appearance): layers of osteocytes surrounding vessels
- lacunae: where osteocytes reside
- canaliculi: interconnect osteocytes by gap junction channels and reach central blood vessel of osteon
- cement line (CL): outer boundary of the osteon
- circumferential lamellae: line entire inner and outer circumferences of the diaphysis
- interstitial lamellae: remnants of previous concentric lamellae
(lamellar bone = mature bone b/c of layers)
23
Q
Inner _________ bone is surrounded by bone marrow and has source of blood from vessels within the bone marrow cavity
A
trabecular
24
Q
- immature or primary bone, usually replaced by lamellar bone (aka nonlamellar or bundle bone)
- characterized by loose arrangement of collagen fibers
- lower mineral content, more cells
- forms during fracture repair and remodeling: alveolar sockets, tendons insert into bone
A
woven bone
25
Q
- laid down in highly organized layers w/ higher mineral content
- replaces woven bone during remodeling and in maintaining compact bone
A
lamellar (mature) bone
27
Q
- type of osteogenesis
- osteoblasts differentiate directly from mesenchyme and begin secreting osteoid
- no cartilage model, no cartilage involvement
- occurs: flat bones of the skull, most facial bones, mandible, central part of clavicle
A
intramembraneous ossification
28
Q
- type of osteogenesis
- hyaline cartilage forms the initial model
- occurs in all bones except some bones of skull and central clavicle
- primary centers of ossification begin late in the 2nd month of development
- secondary centers of ossification are in epiphysis
- completed in early adulthood
A
endochondral ossification
29
Q
What are the 6 steps of endochondral ossification?
A
- hyaline cartilage forms initial model
- perichondrium changes to periosteum (outer surface): osteoblasts form new bone on the surface of cartilage building an outer bony collar surrounding shaft of cartilage model, responsible for bone growth in width (diaphyseal growth)
- embedded central chondrocytes begin calcifying the matrix and begin dying (starving) as bone collar forms
- dying cartilage cells stimulate blood vessels to invade bringing in osteoblastic precursors > osteoblasts, deposit bone matrix on surface of calcified cartilage forming trabecular bone covering calcified cartilage core, this is the primary ossification center, begins forming late in 2nd mo of dvlpmnt
- osteoclasts move in and remove ossified cartilage to create marrow cavity
- secondary ossification centers develop in the head (epiphysis) of long bones through same process beginning around time of birth
30
Q
- hyaline cartilage found between the primary and secondary ossification centers
- bone lengthening is dependent on this cartilage plate
- damage to this plate (e.g. fractures) during growth will disrupt lengthening of the bone
A
epiphyseal growth plate
31
Q
What are the different zones within an epiphyseal growth plate?
A
- resting zone (reserved cartilage zone)
- proliferation zone: chondrocytes within plate undergo mitosis and increase cell numbers forming stacks of chondrocytes (FGFR3 plays key role in maintaining chondrocyte proliferation, autosomal mutations in this receptor are responsible for achondroplasia)
- hypertrophic zone: chondrocytes deposit ECM spreading them apart while they increase in size (interstitial growth), initiate vascular invasion of cartilage, pushing the epiphysis away from diaphysis and lengthening the bone
- calcification zone: cartilage cells calcify surrounding matrix and die
- ossification zone: invading BV’s bring in osteoprogenitor cells that differentiate into osteoblasts and cover hardened cartilage w/ woven bone matrix
(eventually osteoclasts remove ossified cartilage and osteoblasts replace w/ trabecular bone, bony collar of long bone is also added on periphery by appositional growth on the outer surface of long bone)
32
Q
What is the mechanical regulation of bone? (bone design)
A
- anatomy of bone reflects stresses
- bone adapts to force placed on it
- fracture resistant
- exercise increases bone mass; prolonged bed rest or disuse results in bone loss (osteopenia/osteoporosis)
33
Q
How does bone growth in diameter occur?
A
- occurs via osteoblasts in the periosteum
- begins w/ formation of bone collar on the cartilaginous diaphysis
- accompanied by enlargement of the marrow cavity by activity of osteoclasts in the endosteum
35
Q
- process that repairs bone microdamage
- also provides calcium metabolism (500 mg of calcium may enter or leave skeleton each day)
- coupled activity: resorption by osteoclasts (removal) followed by formation of ostseoblasts (replacement), these two must be linked to maintain bone density
- responsible for the concentric lamellar orientation of osteons and for the interlamellar portions (partially removed osteons remaining from previous remodeling events)
A
bone remodeling
36
Q
- type of bone remodeling
- this type of bone is replaced every 3-4 years
- osteoclasts remove (resorb) bone matrix and signal osteoblasts to come in
- osteoblast depost fresh new bone
A
trabecular bone remodeling
37
Q
- type of bone remodeling
- occurs every 10 years
- old osteons are resorbed by osteoclasts, creating tunnels and signaling for BV’s
- osteoprogenitors invade tunnels > osteoblasts > secrete osteoid
- new osteon forms w/ concentric lamellae and trapped osteocytes
- interstitial lamellae remain
A
compact bone remodeling
38
Q
What are the 4 steps of bone fracture repair?
A
- fracture hematoma forms: torn BV’s w/in fracture release blood > clots and produces the hematoma
- fibrocartilaginous (soft) callus forms: hematoma removed by macros > replaced by fibrocartilage-like mass (soft callus) within 2-3 weeks; if torn, periosteum reestablishes continuity over soft callus
- hard (bony) callus forms: procallus invaded by BV’s and osteoblasts; fibrocartilage is replaced by woven bone > forms hard callus within 2 months
- bone is remodeled: woven bone is remodeled as compact/cancellous bone; vasculature is reestablished
39
Q
- bone disorder of low bone mass
- cause: bone resorption is faster than bone deposition
- 30% of caucasian women will experience bone fracture due to this condition
- occurs most often in women after menopause, but also occurs in elderly
- risk factors: strong genetic component, poor diet, insufficient exercise to stress bones, inadequate calcium in diet, insufficient vitamin D
- estrogen deficiency also a risk factor; estrogen therapy used as prevention, however it causes increased risk of CV dz and BrCa, thus its use is controversial
A
osteoporosis
41
Q
- vit D deficiency in children
- analagous to osteomalacia but is more severe
- weakened long bones, abnormal head and rib cage
A
rickets
