MSK- Physiology Flashcards
What are the functions of the skeleton?
- locomotion (movement)
- bone marrow: RBC production
- support
- endocrine regulation
- mineral storage
- protection
How many bones are there in the human skeleton?
206
How many axial and appendicular bones?
axial = 80 appendicular = 126
What are the classifications of bone?
- long bone
- short bone
- flat bone
- irregular bone
- sesamoid bone
Give some examples of each bone…
- long = femur, humerus
- short = carpals and tarsal bones
- flat = skull, scapula
- irregular = vertebrae, clavicle, mandible
- sesamoid = patella
What are the two types of bone?
woven and lamellar
Give some characteristics of woven bone?
- forms quicker than L
- mechanically weak
- no organisation
- no clear structure
- primary bone
Give some characteristics of lamellar bone?
- forms slower than W
- mechanically strong
- highly organised
- clear structure
- secondary bone
- many collagen fibres parallel to other fibres in same layer create osteons
When is woven bone present?
- in ALL foetal bones
- after fractures during repair process
- Paget’s disease
When comparing woven to lamellae what is the comparison in number of osteocytes?
woven bone = more osteocytes per unit volume and higher rate of turnover (spongy bone has NO osteocytes)
What are the two types of secondary bone?
Compact (dense/cortical)
OR
Trabecular (spongy/cancellous)
What are the different types of bone marrow and what do they produce?
Red- produces RBC’s in childhood
Yellow- nutrient reservoir in adults
What are epiphyses?
contain spongy bone and resist compression
What is the periosteum?
outer fibrous layer
What are Sharpies fibres?
perforating fibres attaching tendons (have a rich nerve supply)
What does bone marrow contain?
haemotopoietic tissue and adipocytes
What are the constitutes of bone and what percentages?
Organic compounds = 50-70%
Inorganic compounds = 20-40%
Water = 5-10%
What organic compounds make up bone?
type I collagen (90%), glycosaminoglycans
What inorganic compounds make up bone?
hydroxyapatite and calcium phosphates
What do collagen and minerals do to the bone?
collagen provides elasticity and minerals provide stiffness
What is endochondral ossification?
the formation of bone in which a cartilage skeleton is gradually replaced with a bone matrix
What are the 5 stages of endochondral ossification?
Bone collar formation Cavitation Periosteal bud invasion Diaphysis elongation Epiphysis ossification
What are the stages of bone collar formation?
- periosteum forms around the cartilage
- progenitor cells differentiate into osteoblasts
- osteoblasts secrete osteoid which lines the outer surface of the cartilage forming a bone collar
What are the stages of cavitation?
- calcification of central cartilage occurs (primary ossification centre)
- cartilage hardens, nutrients cannot diffuse to inner compartment therefore it degenerates
- cavities begin to form
What are the stages of periosteal bud invasion?
- periosteal blood vessels invade inner cavity
- through hole called nutrient foramen
- remaining cartilage is broken down by osteoclasts and osteoclasts secrete osteoid forming trabecular (spongy bone)
What are the stages of diaphysis elongation?
- epiphysis lengthens and medullary cavity formed
- blood vessels invade secondary ossification centres in epiphyses
What are the stages of epiphysis ossification?
- spongy bone is formed
- hyaline cartilage left on ends of bones = articular cartilage
- growth plate forms between primary and secondary ossification centres
What are osteoblasts derived from?
mesenchymal cells
What are osteoclasts derived from?
haematopoietic cells / monocytes
When do the growth plates fuse?
they ossify in mid 20’s
What is responsible for the lengthening of bones during childhood?
the growth plates
Which cartilage is particularly responsible to growth hormone and to sex hormones?
epiphyseal cartilage and undergoes increased activity at puberty when the growth spurt occurs
What are the cell layers of endochondral ossification )epiphysis - diaphysis) ?
Resting cartilage Hyperplasia (zone of) Hypertrophy (zone of) Ossification (zone of) Primary bone
What happens during the resting cartilage phase?
resting cartilage begins to divide
What happens during hyperplasia?
cells form column progeny
What happens during hypertrophy?
the cells grow and erode into the cartilage, chondrocytes are reabsorbed and calcified
What happens during ossification?
osteoblasts attach to the calcified substrate and lay down primary bone
What happens during primary bone stage?
at the same time bone is eroded and deposited on the outside of the bone shaft = appositional growth
What is intramembranous ossification?
The laying down of bone straight into mesenchyme
Which bones originate from intramembranous ossification?
Flat bones
When does the process of intramembranous ossification begin?
In 2nd trimester of embryonic life
What are the 4 stages of intramembranous ossification?
- Development of ossification centre
- Calcification
- Woven and trabeculae formation
- Periosteum formation
Describe the first stage of intramembranous ossification…
Development of ossification centre in the fibrous sheath
- progenitor cells transform into osteoblasts
- they secrete an organic extracellular matrix
Name and describe the second stage of intramembranous ossification…
Calcification
- deposition of calcium and other mineral salts
- extracellular matrix calcifies
- trapped osteoblasts become osteocytes
Name and describe the third stage of intramembranous ossification…
woven bone and trabeculae formation
- osteoid forms around embryonic blood vessels forming a random network of trabeculae (NO OSTEONS)
Name and describe the fourth stag of intramembranous ossification…
periosteum development
- peripheral mesenchyme forms into periosteum
- bone closest to periosteum thickens and becomes compact bone either side of central spongy bone
What are lacuna?
pockets where osteocytes sit
What are cannaliculi?
communication between osteocytes
What are perforating volksmann canal
blood from periosteum to blood in central canal
What are lamellae?
thin layers of matrix which comprise solid bone
What is the Haversian Canal?
a longitudinal canal containing blood vessels
When does intramembranous ossification occur?
- formation of flat bones of skull
- formation of jaw and clavicle
- internal fixation of bone healing (not plaster cast)
What is bone modelling?
- gross shape is altered, bone is added OR taken away
What is bone remodelling?
all of the bone is altered, old bone is replaced by new bone
What are the 4 stages of bone remodelling?
- activation
- resorption
- reversal
- formation
What happens in the activation step of bone remodelling?
osteoclasts gather in small pits on the surface of the bone called lacunae
What happens in the resorption step of bone remodelling?
Osteoclasts adhere to the surface of the bone and break down the bone in 2 ways:
- organic component broken down by acidification of matrix
- inorganic component broken down by lysosomial enzymes
What happens in the reversal step of bone remodelling?
- end of the resorption phase
- reverse cells (macro-phage like) remove debris
What happens in the formation step of bone remodelling?
- osteoblasts are attracted to the area by growth factors released from the breakdown of bone matrix
- osteoid secreted from osteoblasts forming a collagen matrix
- the osteoblasts then mineralise this to form new bone
What growth factors are release in the formation stage of bone remodelling?
TGF-beta and FGF’s (fibroblast growth factors)
What enzymes are released during the resorption phase of one remodelling?
collaginases and MMP-9
Describe the steps of osteoblastogenesis…
- wingless-int stimulates MSC’s»_space; osteoprogenitor cells
- osterix stimulates osteoprogentior cells»_space; osteoblasts
Describe the steps of osteoclastogenesis…
- PU-1 and M-CSF stimulates HSC’s»_space; osteoprogenitors
M-CSF stimulates 2 things:
1. proliferation of osteoclast progenitors
2. up-regulation of RANK expression
» osteoclast formation
Give 4 reasons for bone remodelling?
- response to loading (exercise)
- replace woven bone with lamellar bone
- repair damage
- obtain calcium
Osteoclasts have a high expression of what two things?
TRAP and cathepsin K
What does deregulated modelling lead to?
disease
What cells release RANKL?
osteoblasts
How do osteoblasts mineralise the extracellular matrix?
depositing hydroxyapatite crystals within the collagen fibres
How do the osteoblasts create sit for the calcium dn phosphate deposition?
secrete alkaline phosphatase
What is bone called before it is mineralised?
osteoid
What are osteoblasts called when bone is surrounded by a calcified matrix (after mineralisation)?
osteocytes
How much of the calcium we ingest is absorbed?
30%
What is the DRA of calcium?
800mg
What are the major sources of dietary calcium?
dairy products which make up 2/3 of our intake
What are the minor sources of dietary calcium?
cereal, vegetables (broccoli) and cereal
What is the average calcium intake per day?
1000mg