Bone tissue, Case study 4 Flashcards
necrosis
- cell or tissue death
- if blood flow is cut off to femoral head, the bone tissue & marrow will die
- if blood supply stops for a long period of time, bone tissue and joint structure will degenerate
what is a DEXA scan?
what does it measure?
(or DXA) Dual Energy X-ray Absorptiometry
measures mineral component of bone (inorganic) and determines fracture risk
- does not measure info re: levels of organic components (protein) in bone
how does a DEXA scan work?
sends x rays through body w 2 energy peaks
- one peak is absorbed by soft tissue
- one peak is absorbed by bone and so we can see both
osteoporosis
- a loss of bone density
happens when osteoclast activity is greater than osteoblast activity
some factors affecting osteoporosis
- menopause: loss of estrogen results in lack of osteoblast cells to come build bone
- calcium and phosphorus levels in the blood: if too low, increases osteoclast activity
why is weight bearing physical activity used to treat/prevent osteoporosis?
any force on bone stimulates osteoblast cell activity
resistance exercise is best
what drugs are typically used to treat osteoporosis?
bisphosphonate drugs
- slow resorption (process of breaking down bone tissue)
- triggers osteoclast cells to undergo apoptosis
functions of the skeletal system
support - bone is rigid, cartilage is flexi&strong
movement - muscles attached to bones via tendons
storage - Ca & P in bone. Fat in yellow marrow
protection - cranium, ribs, vertebrae
blood cell production - red bone marrow
red bone marrow
produces blood cells and platelets
- replaced by yellow bone marrow as we age
yellow bone marrow
a means of fat storage
types of cartilage
hyaline cartilage
elastic cartilage
fibrocartilage
hyaline cartilage
- fairly strong
- present in moveable joints (ie usually synovial)
- found in nose, trachea (rings)
elastic cartilage
- has elastic fibres in it, along w collagen
- found in external ear
fibrocartilage
- strongest
- found in weight bearing joints (ex. disks b/w vertebrae, meniscus of knee)
- no perichondrium therefore very hard to fix, repair
some things about cartilage
- avascular: must get blood supply from outside
- composed of cartilage cells and matrix
- matrix composed of 70-85% water, proteins, ground substance
main cell type in cartilage is ? tell me more
chondrocyte
located in a cavity called a lacuna
- an immature chondrocyte is called a chondroblast
chondroblast
- produce matrix: collagen, proteoglycans
- produce matrix around them and then get trapped inside the matrix and thus become chondrocytes
perichondrium
- double layer of dense irregular CT that covers most cartilage
- composed of fibroblasts & gets pushed out as chondroblast layer beneath grows
- – the blood vessels and nerve supply for cartilage is here so nutrients and such must diffuse from here
articular cartilage
a type of hyaline cartilage
- no perichondrium therefore, it must get blood supply from nearby bone tissue
what are the name for which cartilage grows?
interstitial growth
appositional growth
interstitial growth
growth from within
- 2 chondrocytes split and secrete matrix between them, this pushed other cells outwards
- occurs during childhood and into adolescence
appositional growth
growth outside of cartilage w chondroblasts
bone composition? what’s it like?
- made of extracellular matrix and bone cells
- bone cells are trapped in matrix, constant breakdown and replacing of old bone matrix
bone matrix
55% inorganic; crystallized mineral salts, white portion of bone, what mineralizes our bones
hydroxyapatite=calcium phosphate crystals
– gives compressive, weight bearing strength
45% organic: collagen / proteoglycans, water
– gives flexible strength
osteoblasts
build bone
- produce collagen & proteoglycans (vesicles)
- form matrix vesicles of hydroxyapatite
- when these vesicles are released, bone matrix is formed (mineral framework and then add organic)
- has extensions called processes, inside of one cell is attached to the inside of another blast cell
osteochondral progenitor cells
stem cells that can become osteoblasts or chondroblasts
can then turn into osteocytes and chondrocytes
osteocytes
- an osteoblast surrounded by bone matrix, located in a cavity called lacuna
- considered inactive
canaliculi of osteocytes
matrix doesn’t form where processes are
- this is where nutrients and oxygen move through towards the cell
osteoclasts
- located on inside and/or outside of bone
- large multinuclear cells, formed by fusion of bone
- resorption
- attaches itself to bone and creates a cavity w protein attachments, plasma membrane ruffles and gives surface area to digest bone
resorption of bone
breakdown of bone
- acid dissolves minerals ( calcium and phosphate)
- enzymes digest proteins / proteoglycans
- fragments of these guys are engulfed and digested
classifications of bone
woven bone
lamellar bone
woven bone
- randomly oriented collagen fibres
- how bones start out and end up when repaired
- remodelled to create lamellar bone
remodelling of woven bone
clast cells break down bone and blast cells rebuild bone into lamellae
- cyte cells are sandwiched between lamellae
lamellar bone
mature bone organized into sheets/layers/rings called lamellae
spongy/cancellous/trabecular bone
- less bone matrix, more space
more affected by osteoporosis bc of surface area - found inside bones: long bones, flat bones, vertebrae
- makes up ~20% skeletal mass
- protected by compact bone
- nutrients rec’d through canaliculi
- osteoctes sandwiched b/w lamellae
why do we need spongy bone?
bc it allows skeleton to be lighter but still sturdy
trabeculae
connecting rods/ plates
- spaces are filled w blood vessels or bone marrow
- oriented along lines of stress (in direction of muscle pulling)
compact/cortical bone
- dense, fewer spaces and only for cells and blood vessels
- found on outside of all bones and shafts of long bones for strength
- makes up ~80% of skeletal mass
name the diff ways that lamellae are organized in compact bone
- concentric lamellae
- circumferential lamellae
- interstitial lamellae
blood vessels are found within compact bone organized in which ways?
as perforating canals (Volkmann)
and as central canals (Haversian)
concentric lamellae
- organized in osteons (osteon is the cylinder of bone tissue)
- rings form around blood vessels (Haversian)
- blood gases and nutrients diffuse outwards
circumferential lamellae
- lamellae sheets that line of the bone of the bone (around the outside hence, “circumference”)
interstitial lamellae
columns formed in spaces between osteon circles
- are the leftover remnants of osteons that were broken down previously
perforating canal
aka Volkmann canal
- carry blood vessels
- run perpendicular to the long axis in bone
think perforating as in they perforate the periosteum
central canal
Haversian
- blood vessels that run parallel to long axis of bone
the layers of periosteum are
outer - dense fibrous layer
inner - osteogenic layer
dense fibrous layer of periosteum
outer layer of periosteum
- contains periosteal arteries and veins (blood supply to bones)
inner osteogenic layer of periosteum
contains osteoblast, osteoclasts and osteochondral progenitor cells
endostenum
connective tissue lining all internal surfaces of bones
ex. medullary cavity, spongy tissue, Volkmann’s canals, Haversian canals
medullary cavity
contains yellow bone marrow
- infants born w red bone marrow here and it is replaced by yellow bone marrow as we age
diaphysis
shaft of long bone - mostly compact bone
epiphysis
end of long bone - mostly spongy bone
metaphysis
the bit between the diaphysis and epiphysis
osteogenesis/ossification
- the process of forming bone tissue
- begins in embryo at 8 weeks, when blood vessels start forming
- mesenchyme becomes osteochondral progenitor cells
types of bone development
- intramembranous ossification
- endochondral ossification
both ways produce woven bone which gets remodelled into lamellar bone
explain the process of intramembranous ossification
- mesenchyme cells create a membrane of connective tissue made of a collagen fibre framework
- osteochondral progenitor cells become osteoblast cells that start to ossify the membrane at 8 weeks
explain the process of endochondral ossification
- mesenchyme cells become osteochindral progenitor cells, turn into chondroblasts that form a hyaline cartilage skeleton
- blood vessels invade perichondrium of hyaline cartilage, stimulates osteochondral progenitor cells to become osteoblasts
- perichondrium becomes the periosteum
how does bone growth occur
appositional growth of bone tissue only: formation of new bone on the surface of old bone at epiphyseal plate w cartilage
- no interstitial growth bc bone matrix is too rigid
growth of bone in length
- takes advantage of interstitial growth of cartilage at epiphyseal growth plates
- from bottom to top (anatomically) we have 4 zones of hyaline cartilage :
zone of resting cartilage
zone of proliferating cartilage
zone of hypertrophic cartilage
zone of calcified cartilage
zone of resting cartilage
contains very slowly dividing chondrocytes (interstitial)
- stays connected to epiphysis
zone of proliferating cartilage
rapidly dividing chondrocytes that divide into what looks like stacks of coins
zone of hypertrophic cartilage
chondrocytes enlarge and mature, then secrete matrix vessels containing hydroxyapatite which starts to calcify the zone above it
zone of calcified cartilage
chondrocytes die off and blood vessels and osteoblasts invade into this area from the endosteum
growth of bone thickness
- osteoblasts beneath the periosteum lay down bone matrix and periosteal ridges form around the region where there’s a blood vessel
- ridges meet forming a tunnel that pinches off , periosteum becomes endosteum of the tunnel
- osteoblasts from the endosteum form new concentric lamellae, (build towards blood vessel)
- osteoblasts from periosteum from new circumferential lamellae
bone remodelling
continuous action of osteoclast and osteoblast activity
- as we grow w age, we need to increase the size of medullary cavity while thickness of bone remains relatively constant
- it takes 10 years for entire skeleton to be rebuilt
