Cartilage and Bone tissue Flashcards
What cell type can create both cartilage and bone tissue?
Mesenchymal stem cells
What is the function of cartilage?
Absorb shock and resist compression
What is cartilage mostly made of?
60-80% water
What covers cartilage?
Perichondrium - Dense irregular CT that resists outer expansion of cartilage when compressed and contains mesenchymal cells that will differentiate into chondroblasts and chondrocytes
Describe the innervation and vascular supply of cartilage?
NONE! No nerves and no blood vessels within the cartilage
How does cartilage receive nutrients?
Diffusion from other surrounding tissues
How is cartilage’s ability to repair itself when damaged?
BAD.. cannot really repair itself at all
What are the cell types of cartilage?
Chondroblasts and chondrocytes
Function of chondroblasts?
Build cartilage matrix and terminally differentiate into chondrocytes
Function of chondrocytes?
Mature cells embedded within cartilage ECM in space known as lacunae
What is in the ECM secreted by cartilage cells?
Ground substance and fibers
What fiber is always present in ECM of cartilage cells?
Type 2 collagen, some cartilage types will add other types as well
Describe the properties of hyaline cartilage
Great shock absorber and most abundant; covers ends of adjoining bones in movable joints
- shiny, glassy, smooth appearance, key role in bone growth
Describe the properties of elastic cartilage
ECM contains more elastic fibers as well as some collagen type 2 which makes it more flexible and can tolerate repeated bending while maintaining shape
Where would you find hyaline cartilage?
Ends of movable joints, layrnx, trachea, nose, sternum/ribs
Where would you find elastic cartilage?
Eustachian tube, auricle of ear, auditory tubes
Describe the properties of fibrocartilage
Tough, resists tension and compression
ECM contains thick type 1 collagen and type 2
Chondrocytes arranged in rows of isogenous groups and fibers arranged in direction of functional stress
Where would you find fibrocartilage?
IV disks, pubic symphysis and some joint capsules
Describe the properties of articular cartilage
Similar to hyaline cartilage but lacks perichondrium, collagen fibers run perpendicular to tissue surface and creates 4 zones
Where would you find articular cartilage?
On surfaces of movable joints
What cartilage types lack a perichondrium?
Fibrocartilage and articular cartilage
What is chondrogenesis and how many ways can it be performed?
Growth of cartilage and can occur in 2 ways
What are the 2 types of chondrogenesis?
Interstitial growth and Appositional growth
Describe appositional growth
Chondroblasts building one layer on top of another
Describe interstitial growth
Chondrocytes within the cartilage divide and form isogenous groups
They then deposit a new ECM to spread and expand the cartilage
How can you differentiate interstitial growth?
The new territorial matrix formed from the new ECM stains differently
Why is it difficult for cartilage to repair itself?
Avascular and low metabolic rate, but is better off in children
What is bone?
Solid connective tissue and a living organ that is well vascularized and innervated
Where do nerves innervate bone?
Periosteum
Where do blood vessels run?
Within canals in bone
What are the functions of bone?
Support, movement, protection, mineral storage, blood-cell formation
What are the bone cell types?
Osteoprogenitor (osteogenic), osteoblasts, osteocytes, osteoclasts
Describe osteoprogenitor cells
Mesenchymal stem cells in the periosteum and endosteum that will create osteoblasts
Describe osteoblast cells
Build bone, mononuclear, housed on bone surfaces
They produce the osteoid and control mineralization of ECM
What is the osteoid?
Bone matrix
What are the 3 fates of osteoblasts?
- actively building bone, cuboidal shaped, become osteocytes
- Quiescent, line bone surface as flat cells
- death by apoptosis
Describe osteocyte cells
Mature osteoblasts in osteoid lacunae; sense strain on bone and control osteoblasts and osteoclasts
What connects osteocytes
Canaliculi - small channels that pass nutrients
Describe osteoclast cells
Resorb bone, multinucleated, create divots and tunnels in bone
What is the fate of osteoclast cells?
Apoptosis
Knobby regions at the proximal and distal end of bone
Epiphysis
Elongated shaft of bone
Diaphysis
Area of bone between epiphysis and diaphysis that consists of spongy bone
Metaphysis
Hyaline cartilage in metaphysis of children long bones that is necessary for elongation of bones
Epiphyseal plate
Once the epiphyseal plate fuses it becomes
Epiphyseal line
Cylindrical space in diaphysis containing bone marrow
Marrow cavity
Dense irregular CT covering external surface of bone
Periosteum
CT lining of all trabeculae and marrow cavity
Endosteum
Describe cortical bone (compact)
Outer walls, lamellar layers are either in circumferential or partial ring arrangement
Describe trabecular bone (cancellous/spongy)
Internal porous network of bony plates and rods at proximal and distal ends more towards the middle
No osteons, can be either woven or lamellar
Woven bone
Immature, new bone that was laid down in a quick, irregular pattern with low mineral content
Lamellar bone
Mature, laid down in organized layers with high mineral content and eventually replaces the woven bone during remodeling!
What is the osteon?
Cylindrical, layered structures comprising mature compact bone
What forms the concentric lamellae?
Osteocytes and matrix arranged into layers around the vessels
Osteocytes reach the blood vessels of the osteon via what?
Canaliculi
What lines the entire inner and outer circumference of diaphysis
Circumferential lamellae
What are the remnant of previous concentric lamellae called?
Interstitial lamellae
Where does trabecular bone receive nutrients?
Surrounded by bone marrow so thats its source
What are the 2 methods of osteogenesis?
Intramembranous ossification and endochondral ossification
Bone formed directly from mesenchymal cells
Intramembranous ossification
Bone formed directly from hyaline cartilage
Endochondral ossification
What bones are from from intramembranous ossification?
Flat bones of skull, most facial bones and central clavicle
In both types of osteogenesis, what type of bone is formed first?
Woven bone
What are the basic endochondral ossification steps?
Perichondrium becomes the periosteum
Osteoblasts build bony collar
Chondrocytes within begin to calcify and die
Osteoblasts deposit bone matrix on calcified cartilage
– forms primary ossification center
Osteoclasts remove ossified cartilage
–forms marrow cavity
Secondary centers of ossification develop in epiphysis
Bone lengthening is dependent upon what?
Epiphyseal growth plate
Where is the epiphyseal growth plate?
Between the primary and secondary ossification centers (metaphysis)
What are the zones in the epiphyseal plate?
Resting zone Proliferation zone Hypertrophy zone Calcification zone Ossification zone
What happens at the proliferation zone of the epiphyseal plate?
Cartilage cells (chondrocytes) undergo mitosis and increase cell numbers
What is needed for correct proliferation at the proliferation zone?
FGFR3
What occurs without FGFR3
Achondroplasia = dwarfism; Shortening of long bones!
Autosomal dominant, defects in cranial base and spinal curvatures
What happens at the hypertrophy zone of the epiphyseal plate?
Chondrocytes enlarge and secrete ECM which spreads the cells apart and they increase in size
THIS LENGTHENS THE BONE by pushing the epiphysis further from the diaphysis
What happens at the calcification zone of the epiphyseal plate?
Cartilage cells calcify and die
What happens at the ossification zone of the epiphyseal plate?
Blood vessels invade and bring along precursors for osteoblasts that cover hardened cartilage with woven bone matrix
Why would bone remodel?
Repair microdamage and calcium metabolism
How much calcium can leave or enter the bone each day?
500 mg
What is responsible for the concentric lamellar orientation of osteons and for the interstital lamellae?
Remodeling of cortical bone
How often is trabecular bone replaced?
Every 3-4 years
How often is cortical bone replaced?
Every 10 years
Describe the process of cortical bone remodeling
-Osteoclasts tunnel though old bone forming a remodeling tunnel
-Osteoclasts signal for blood vessels to follow
-Mesenchymal cells follow blood vessels and become osteoblasts
-Osteoblasts begin depositing concentric rings of lamellar bone around the blood vessel until the tunnel is filled in
New osteon is formed!
Describe the process for fracture repair?
- Torn blood vessels within fracture clot and form hematoma
- Inflammation
- Hematoma removed by macrophages and replaced by soft callus from mesenchymal stem cells that create fibrocartilage and hyaline cartilage there
- Bone callus forms using endochondral ossification(osteoblasts from woven trabecular bone)
- Bone remodeling - woven bone replaced with lamellar bone and vascularization re-established
Condition due to low bone mass; bone resorption is occurring faster than bone building
Osteoporosis
What is controversial about osteoporosis treatment in post-menopausal women?
Estrogen inhibits bone loss, so without it, bone is lost faster
Estrogen replacement therapy has side effects such as cardiovascular risks and breast cancer
What is vitamin D needed for?
Calcium absorption in the gut
Osteomalacia
Occurs in adults; softening of bones due to defective mineralization
Rickets
Occurs in chidlren; more severe than osteomalacia
Weakened bones, abnormal head and ribs
