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