Outcome 3 - Bone Tissue Flashcards
What are some fun facts about bone tissue?
- each individual bone is considered an organ
- they are constantly being remodeled
- bone tissue makes up ~18% of your weight
What are the six major functions of bone?
- Support
- Protection
- Aid in movement
- Mineral homeostasis
- Blood cell production
- Triglyceride storage
What is the red bone marrow?
it is a network of reticular fibres that contains blood cells, adipocytes, fibroblasts and macrophages
What is yellow bone marrow?
it is made up of adipose cells (which store tg)
What are long bones?
bones that are greater in LENGTH than width
What are the parts of long bones?
- epiphysis (ends)
- diaphysis (‘body’)
- metaphysis/epiphyseal line (“growth plate” in peds)
- articular cartilage (that protects epiphysis)
- periosteum (2 layers (inner - very immature bone cells) covers the bone)
- medullary cavity (contains marrow; red in adolescents and yellow in adults)
What is the difference between epiphyseal plate and epiphyseal line?
plate is seen in GROWING bones while the line is seen in MATURE bones
- in the plate, you see. hyaline cartilage to allow diaphysis to grow while in line, the cartilage is ossified
What is the articular cartilage responsible for?
it is a thin later of hyaline cartilage that reduces friction, and absorbs shock
forms the joint with another bone
What is the periosteum?
it is a 2 layered tough sheath of connective tissue that covers the entire bone (except for where the joint is)
What are the two layers of periosteum?
- outer fibrous layer
- inner osteogenic layer
What is the difference between the fibrous and osteogenic layer?
Osteogenic - has osteogenic cells that differentiate to osteoblasts
fibrous - dense irregular connective tissue
Osteoblasts are bone forming cells that allow for the lengthening of bone not thickening. T/F
False!
osteoblasts are bone forming cells but they allow for the thickening of bone NOT LENGTHENING
How are periosteum attached to bone tissue?
by perforating fibres (aka Sharpey’s fibres) - bundles of collagen fibres extending from periosteum to ECM of bone
What is the medullary cavity?
it is the hollow space in the diaphysis that holds yellow bone marrow and blood vessels
- hollowness minimizes the weight of bone
What is the endosteum?
a thin, single layer of bone forming cells and some connective tissue that lines the medullary cavity
Remember that connective tissues are made up of extracellular matrix and cells.
What is in the ECM of bone tissue?
- 15% water, 30% collagen fibres, 55% crystallized mineral salts
- Ca3(PO4)2 + Ca(OH)2 –> Ca10(PO4)(OH)2 [hydroxyapatite] which hardens around collagen and crystallize for hardened tissues
What is calcification?
It is the process of tissue hardening due to deposition of salt minerals into collagen fibre network
What are the 4 types of cells that are present in bone tissue?
- osteogenic (osteoprogenitor) - bone stem cells; develop into osteoblasts
- osteoblasts - bone forming; forms bone ecm
- osteocytes - maintains bone tissue
- osteoclasts - WBCs lineage –> large, phagocytic cells to break down bone tissues
Where do you find osteogenic cells?
the inner portion of the periosteum, in the endosteum, and the canals that house blood vessels
What are osteogenic cells derived from?
mesenchyme cells
What is the responsibility of osteoblast cells?
- secreting collagen fibres and ECM
- start the calcification process in bone tissue
Where do you find osteoblast cells?
the outer surfaces surrounded by ecm which results in them becoming trapped deep in the bone tissue where they become osteocytes
What are osteocytes? Role?
primary, and mature cells found throughout the bone tissues
- maintain metabolism within cells
What are osteoclasts? Where are they found?
huge cells derived from monocytes; ruffled ends of the cell secretes acids and enzymes to break down bone tissue
- in the endosteum
What is resorption?
the breakdown of bone ECM for normal repair, development, growth and maintenance
What are the two types of bone classification?
1) compact (80%)
2) spongy (20%)
What parts make up compact bones?
- osteons
> concentric lamellae (circular plate of calcified bone matrix surrounding the central canal)
–> central canal (where blood vessels and nerves are) - interstitial lamellae (areas between neighbouring osteons)
> lacuna (‘lake’ that has osteocytes)
> canaliculi (branches that allow for communication, and routes for nutrients and waste)
Where are compact bones found?
beneath the periosteum and makes up the majority of the shaft of long bones
- connected to the periosteum by sharpey’s fibres
What are perforating canals (aka Volkman’s canals)?
- it contains blood and lymphatic vessels and nerves from the periosteum
- it allows for the connection between central canals and medullary cavity
What is different about spongy bones?
- they don’t have osteons but their concentric lamellae is found in the trabeculae*
- contain lamellae in irregular patterns of thin columns known as trabeculae
- major tissue in short, flat, sesamoid and irregular shaped bones
- lighter than compact bones
- support and protect red marrow
Where is bone marrow specifically found?
in the spaces between trabeculae
What is hematopoiesis?
the formation of blood cells
Where does hematopoiesis occur in infants? adults?
infants - everywhere
adults - spongy bones mainly in axial skeleton (trunk): HIP, PELVIS, RIBS, VERTEBRAE, STERNUM and PROXIMAL HUMERUS AND FEMUR
What is the nutrient artery?
the largest artery found in bones (mainly long bones), that carry blood to the bone tissue
- usually through the diaphysis (sometimes through metaphysis)
What is the difference in bone vasculature in adult bones and adolescent bones?
in adolescent bones, the nutrient artery does not feed pass the epiphyseal plate whereas in adult bones, the nutrient artery will supply blood to the epiphysis area as well!
What are the different types of arteries found in bone tissue and where do they supply blood?
- periosteal - enters the diaphysis through perforating canals and supplies the periosteum and OUTER portions of compact bone
- nutrient - center of diaphysis, enters through nutrient foramen; can be more than one, and supplies INNER part of diaphysis
- metaphyseal - supplies the metaphysis
- epiphyseal - supplies the epiphysis
Where are nerves found in spongy bones?
along the trabeculae of epiphysis, metaphysis and especially in the growth plate!
The pain from having a bone marrow biopsy is due to passing through the periosteum which has many sensory nerves. T/F
TRUE!
there will be little pain when the needle is actually in the bone and marrow!
What is ossification?
the process in which bone is formed
What type of cells do all connective tissue come from?
mesenchymal cells
What are the 4 situations in which ossification occurs?
- initial bone formation (in utero)
- growth (length and thickness)
- fracture repair
- remodelling (resorption and deposition)
What are the two types of initial ossification?
1- intramembranous
2- endochondral *most long bones are formed by this type
What are the steps to intramembranous initial ossification?
- developing ossification center where osteoblasts secrete organic ECM
- calcification by calcium and other mineral salts being deposited and ECM hardening
- ECM develops into trabeculae that fuses to form spongy bone
- mesenchyme at the periphery of the bone develops into periosteum
What are the steps to endochondral initial ossification?
- mesenchymal cells develop into chondroblasts which form the cartilage model
- growth of cartilage occurs by cell division of chondrocytes
- develop primary ossification center (diaphysis) where bone tissue replaces most of the cartilage *artery enters the diaphysis; growth starts OUTSIDE inwards
- osteoclasts now break down some of the bone tissue to form the medullary cavity
- development of secondary ossification in the epiphysis *artery enters the epiphysis; growth starts INSIDE outwards
- form articular cartilage and epiphyseal plate
what are the 4 zones of the epiphyseal plate?
- resting cartilage
- proliferating cartilage
- hypertrophic cartilage
- calcified cartiliage
When does the growth plate close?
between 14-24
sooner in females than males
What is the zone of resting cartilage?
area where cells anchor the plate to the epiphysis
contains scattered chondrocytes
What is the zone of proliferating cartilage?
contains larger, stacked chondrocytes
- chondrocytes will divide to replace those that die at the diaphyseal side of the growth plate
What is the zone of hypertrophic cartilage?
- contains large chondrocytes that are maturing and also arranged in columns
What is the zone of calcified cartilage?
layers of only a few cells thick of large mature cells
- where cells start to die due to calcification of ECM
- newly calcified cartilage will be destroyed by osteoclasts
- osteoblasts and capillaries from diaphysis will invade the area
Epiphyseal side has the cartilage and the diaphyseal side will contain the newly formed bone. T/F
True.
What is appositional growth?
the growth of the width of bones
How does appositional growth occur?
- cells at the surface of the periosteum differentiate into osteoblasts (secrete ECM and collagen fibres)
- osteocytes develop and form ridges for periosteal blood vessels
- ridges fuse and form an endosteum-lined tunnel
- osteoblasts build new concentric lamellae to form new osteon
- bone grows outward and process is repeated as ridges form again
Bone starts developing ___ after conception.
6 weeks
Bone stops growing completely after the epiphyseal line is formed. Even width-wise. T/F
False.
it’ll continue to grow in thickness and in diameter as a response to stress from increased muscle activity or weight
What is bone remodelling?
replacement of old bone with new bone through processes of resorption and deposition
what’s deposition? resorption?
deposition - addition of minerals and collagen fibres to bone by resorption…
resorption - removal of mineral and collage fibres from bone by osteoclasts
how does resorption occur?
osteoclasts:
- form a leak proof seal at the edge of ruffled borders
- release lysosomal enzymes and several acids
- enzymes break down fibres and acid breakdown bone minerals
- endocytosis occurs to “suck up” the degraded protein
- deposition through exocytosis where substances will then diffuse into nearby capillaries
In a bone scan, what would it look like in normal adult remodelling?
areas undergoing remodelling will be gray
In a bone scan, what would it look like in places where deposition is higher?
black because the bones are taken up more phosphate/calcium
In a bone scan, what would it look like in places where resorption is higher?
white, because the bones are breaking down the bone tissue for minerals not taking up minerals
What are minerals that are needed for bone growth and remodelling?
Ca + P (makes bone ecm hard)
F (help form ECM), Mg (helps strengthen ECM), Fe and Mn (activates enzymes involved in synthesis of ECM)
What vitamins are needed for bone growth?
- vitamin c - for collagen synthesis
- Vit K/B12 - for protein synthesis
- vit a - stimulation of osteoblasts
- vit d - for absorption of Ca by GI tract (vit d’s active form = calcitriol)
What factors affect bone growth?
- minerals
- vitamins
- hormones (hGH stimulates production of – IGF and sex hormones)
What is the number one hormone in childhood to affect growth?
insulin-like growth factors which is produced by liver and bone tissue to promote osteoblasts and cell division and protein synthesis
What hormones are responsible for closing the epiphyseal plate? What else are they responsible for?
sex hormones; they’re also responsible for the stimulation of osteoblasts and growth spurts
Why do women typically suffer from osteoporosis?
because of estrogen!
it promotes apoptosis of osteoclasts (increase in resorption but less bone building)
What are the other types of hormones that effect bone?
PTH and Calcitonin
What is the Ca blood plasma level?
9-11 mg/100 ml
Describe the negative feedback loop of PTH on Ca levels.
decreased level of blood ca2+
parathyroid gland cells detect lowered calcium levels
PTH gene turned on – increase release of PTH
osteoclasts are now increasing bone resorption and kidneys are retaining ca2+ in blood and produce calcitriol (which is responsible for the ca2+ reabsorption in GI tract)
increase blood ca2+
What hormone decreases blood Ca2+ levels?
calcitonin (secreted by parafollicular cells in thyroid)
it promotes bone formation and inhibits osteoclast activity
What are two principle effects of aging?
1) demineralization - decrease of Ca and other minerals (increase when sex hormones decrease)
2) brittleness - decrease in protein synthesis due to decrease in hGH which results in increase of fracture probability
deposition > resorption (growth) - __________
deposition = resorption - _____________
d > r – birth to adolescence
d = r – young adults
What are the categories of fractures (#)?
complete, incomplete
open, closed
traumatic
pathological/fragility/insufficiency
stress
occult
what is the difference between complete and incomplete fractures?
complete - right through the bone, disrupting both cortical surfaces
incomplete - one cortical surface disrupted, bone still in one bone
what is the difference between open and closed #?
open - breaks through skin (aka compound #)
closed - doesn’t break through the skin
What is an impacted #?
impacted - one end of the fractured bone is driven INTO the interior of the other bone
What is a comminuted #?
bone is splintered, crushed or broken into pieces at the site of impact; has smaller bone fragments between the two main fragments
What is a greenstick #?
type of incomplete # which means that one cortical layer is broken, and the other side is bent
*only occurs in children
What are traumatic #?
caused by external force acting on the body
What is pathological/insufficiency/fragility #?
occurs as a result of a pathological condition that weakens the bones
What are stress #?
Repetitive, low stress injury to bone
Results in microscopic cracks in bone
What are occult #?
Fractures that are not seen in normal radiographs
What are the steps in fracture repair?
- Reactive phase
2a. Reparative phase: fibrous cartilage formation
2b. Reparative phase: bony callus formation - Bone remodelling
What is occurring in the reactive phase?
Inflammatory.
- the blood vessels crossing the fracture is broken
- after 6-8 hours, a mass of blood forms (fracture hematoma)
- bone cells die due to lack of blood circulation
- swelling and inflammatory happens
- phagocytes and osteoclasts begin to remove dead/damaged tissue
What is occurring in the reparative phase that results in fibrous cartilage callus formation?
- blood vessels grow into the fracture hematoma
- fibroblasts from periosteum invade fracture site and produces collagen fibres
- some cells develop into chondroblasts which results in fibrous cartilage
- cartilage then bridges the fracture gaps
What is occurring in the reparative phase that results in bony callus formation?
- at the area that is well-vascularized, osteoprogenitor cells (aka osteogenic) develop into osteoblasts
- osteoblasts then start to produce spongy bone trabeculae
- spongy bone trabeculae join living and dead portions of the bone
- fibrous cartilage then is converted into spongy bone
What is occurring in the bone remodelling phase?
- dead portions of the original fragment is absorbed by osteoclasts
- compact bone replaces spongy bone around the periphery of the fracture
How do you determine if a bone has been healed after a fracture?
A thickened area on the surface of the bone
