Cartilage and Bone
metaphysis
wider portion adjacent to the growth plate
why can cartilage undergo interstitial growth whereas bone cannot?
Bones can't undergo interstitial growth because their growth cells are only on the outside
why is bone remodeling important?
it repairs damage and helps with calcium metabolism
what has menopause have to do with an increased risk for developing osteoporosis?
Menopause makes estrogen levels low, which can cause loss of bone mass
how does the process of remodeling compact bone result in the formation of osteons?
Remodeling is responsible for the concentric lamellar orientation of osteons and for the interlamellar portions (partially removed osteons remaining from previous remodeling events)
describe the steps involved in lengthening of bones
a. Bone lengthening depends on the epiphyseal plate. i. Cartilage within the plate undergoes interstitial growth forming stacks of chondrocytes ii. Cells then deposit extracellular matrix spreading the chondrocyte cells apart from one another while they also increase in cell size. This is interstitial growth iii. This pushes the epiphysis away from the diaphysis lengthening the bone iv. Older cartilage cells then calcify the surrounding matrix and die v. Osteoblasts cover the hardened cartilage with bone matrix vi. Eventually osteoclasts remove this ossified cartilage and osteoblasts replace it with new trabecular bone
unique properties of cartilage
a. Cartilage is a firm but flexible supporting tissue containing a large amount of tissue fluid (80% water) b. Tough, resilient, great shock absorber and resists compression c. Not innervated and is avascular d. If damaged, difficult or impossible to repair itself
osteosarcoma
a. Form of bone cancer primarily affecting young individuals between 10-25 b. Usually originating in long bones of limbs c. Survival rates is 60-70% if found early
describe the steps involved in early endochrondral ossification of long bones
a. Hyaline cartilage forms initial model b. Perichondrium changes to periosteum. Osteoblasts form new bone on surface of the cartilage building an outer bony collar surrounding the shaft of the cartilage model. Responsible for bone growth in width c. Embedded chondrocytes begin calcifying the matrix and begin dying as the bone collar forms d. Dying cartilage cells stimulate blood vessels to invade bringing in osteoblasts. Osteoblasts deposit bone matrix on top of the dead calcified cartilage forming trabecular bone covering a calcified cartilage core. This area is referred to as a primary center of ossification e. Osteoclasts then move in and remove the ossified cartilage to create a marrow cavity f. Secondary centers of ossification begin developing in the head of the long bones through the same process beginning about the time of birth
how does the rate of bone formation and bone resorption typically change during one's lifetime?
a. In children and adolescents- bone formation exceeds bone reabsorption i. Calcium needs are high, skeleton grows until 18-21 years old b. In young adults- bone formation and bone reabsorption are in balance c. In old age- resorption predominates, bone mass declines, and calcium needs tend to be high due to poorer nutritive absorption.
osteoarthritis
a. Long-term degenerative condition b. Normal use causes joints to release metalloproteinase enzymes that break down the cartilage matrix while chondrocytes repair the damage by secreting more matrix. When strain on the joint is excessive or repeated, too much of the enzyme is thought to be released, causing OA
osteopororsis
a. Low bone mass b. Bone resorption faster than bone deposition
describe the structural organization of the osteon
a. Osteocytes must be within 3-4 layers of a blood vessel b. Has a central canal containing blood vessels and nerves providing osteocytes with a source of nutrition and oxygen (vessels referred to as a Haversian vessel) c. Osteocytes and matrix are arranged in concentric layers surrounding the vessels d. Canaliculi interconnect osteocytes and reach to central blood vessel of osteon
what happens if an individual has a prolonged deficiency in vitamin D?
a. Osteomalacia- softening of bones due to defective mineralization b. Rickets- occurs in children and is analogous to osteomalacia
functions of bone organs
a. Support- structural framework for the body b. Movement- act as levers for skeletal muscles c. Protect underlying organs d. Mineral storage- calcium e. Blood-cell formation- provides a protective space for red marrow
how does cartilage grow?
appositional and interstitial growth
greenstick fracture
bone breaks incompletely, one side of bone shaft breaks but the other side doesn't
compression fracture
bone is crushed
comminuted fracture
bone is fractured in 3 or more places
osteoblasts
builds bones i. Cuboidal in shape, single nucleus ii. Located on bone surface iii. Produce bone matrix and control mineralization of extracellular matrix iv. Fate- eventually become embedded within bones and become osteocytes, quiescent ones rest on bone surface as flat bone lining cells, death by apoptosis
chondroblasts
builds the cartilage matrix and are located next to the perichondrium and within cartilage growth plates
hydroxyapatite
calcium and mineral salt crystals of inorganic molecules of the ostoid. Makes up 65% of bone matrix
articular cartilage
cape of hyaline cartilage found at ends of bones articulating with other bones
appositional growth
chondroblasts next to perichondrium deposit one layer of cartilage on top of another i. apply one layer on top of another
osteoclasts
cleaners; removes bone tissue (bone resorption) i. Macrophage like; dissolve bone matrix by secreting acids and proteases degrading the bone matrix ii. Multinucleated cells residing on bone surfaces iii. Create divots on bone surfaces or they can carve tunnels within the bone iv. Fate- apoptosis
periosteum/endosteum
connective tissue found on the outer surface and inner surface of hollow bones; contains osteogenic mesenchymal stems cells
endochondral bone formation
develops on a cartilage model or surface
list the primary sources of vitamin D
diet (dairy and fish), UV sunlight, dietary supplements
epiphyseal
epiphysis separates from diaphysis along the epiphyseal plate; will stunt growth in children and adolescents
interstitial growth
expanding from within the tissue; chondrocytes within cartilage divide forming isogenous groups (nests). Each cell then secretes a new extracellular matrix between one another so they become increasingly separated from one another i. Push away from each other
elastic cartilage
flexible and able to tolerate repeated bending while maintaining its shape i. Contains many elastic fibers within extracellular matrix ii. Location- ear, epiglottis, Eustachian tube
intramembranous bone formation
formed directly from mesenchyme, no cartilage involved i. Only gets bigger by appositional growth where osteoblasts keep adding bone to the outer surface layer by layer
where do chondroblasts, chondrocytes, and osteoblasts come from?
formed from mesenchymal cells
trabecular (cancellous) bone
forms a network of bony plates or rods surrounded by bone marrow i. No osteons found here ii. Found at proximal and distal ends of long bone
compact (cortical) bone
forms outer walls of bones i. Primary structure consists of layers either in a circumferential arrangement or partial rings
hyaline cartilage
great shock absorbing properties; most abundant type i. Covers ends of adjoining bones in moveable joints ii. Glassy, shiny, smooth surface iii. Key role in bone development and growth iv. Location- found in joint surfaces, costal cartilage, larynx, trachea, bronchi, nose
medullary cavity
hollow area, marrow cavity
epiphyseal plate
hyaline cartilage plate within metaphysis of children and adolescents; necessary for elongation of bones
three main types of cartilage
hyaline, elastic, and fibrocartilage
extracellular matrix
i. Ground substance containing hyaluronic acid, proteoglycans, glycoproteins, and water ii. Elastin or type I collagen, depending on the type of cartilage
describe the basic steps involved in the body's repair of a broken bone
i. Hematoma formation- fracture of blood vessels in the bone and clots form ii. Fibrocartilaginous callus formation- mesenchymal stem cells in periosteum and endosteum adjacent to the injury site begin generating chondrogenic precursor cells that invade the clot. Forms a soft callus of dense fibrous connective tissue that contains both fibrocartilage and hyaline cartilage iii. Bony callus formation- osteoblastic precursors invade and begin forming trabecular bone within soft callus by endochondral ossification thus forming a hard callus iv. Bone remodeling- bony callus is remodeling and replaced by compact bone
what does an ostoid contain?
i. Organic matrix- type I collagen and proteoglycans ii. Inorganic molecules- calcium and mineral salts
endosteum
layer of cells lining the internal surfaces of bone, specifically, lining the central canals of osteons and the medullary cavity, and veering the trabeculae of spongy bone
diaphysis
main middle shaft
chondrocytes
mature cells that are embedded within the extracellular matrix in a space referred to as a cartilage lacuna
perichondrium
membrane of fibrous connective tissue that covers external surface of cartilage i. Helps resist outer expansion of cartilage when compressed
periosteum
membrane of fibrous connective tissue that covers the external surface of bones
cell types present in bone tissue
mesenchymal stem cells, osteoblasts, osteocytes, osteoclasts
mesenchymal stem cells
on outer and inner surfaces of bones; make other cells
how are osteoblasts and osteoclasts involved in the process?
osteoclasts remove (clean) bone osteoblasts replace (build) bone
depressed fracture
portion of the bone is pressed inward
spiral fracture
ragged break due to twisting forces
osteocytes
residents inside the bone; osteoblast that has become embedded in the bone matrix and is occupying a space called lacunae i. Interconnected with each other via small channels called canaliculi, receive nutrients through channels, communicated with each other through gap junctions ii. Function is to sense strain on bone and help monitor the condition of the bone tissue; controls activity of osteoblasts and osteoclasts
bone tissue
rock hard connective tissue; comprised of cells embedded in a mineralized extracellular matrix i. Support and protect body structures ii. Very strong and fracture resistant
epiphysis
rounded end
primary and secondary osteogenic centers
sites of bone formation within the cartilage of developing long bones
canaliculi
small channels in the bone matrix connecting osteocytes
lacunae
space an osteocyte resides
mesenchymal cells
stem cells for connective tissues
ostoid
the bone extracellular matrix
where can mesenchymal cells be found?
they can be found in all connective tissues and in the perichondrium
what type of collagen is found in all forms of cartilage?
type II collagen
fibrocartilage
very tough, resists strong compression and tensional forces i. Contains thick type I collagen and type II collagen ii. Location- intervertebral disks, pubis symphysis joint, menisci of long bone joints
bone organ
well vascularized and well innervated