introduction to the limbs Flashcards
bones: explain and contrast the basic mechanisms of intramembranous and endochondral bone development; outline the properties of bone, and recall the different types of bone organisation in relation to function; recall the mechanisms of appositional growth of bones, long-bone elongation and bone remodeling. Understand the basic mechanisms involved in bone fracture healing
5 functions of bone
support of body shape, system of levers for muscle action, protection of internal organs, site of blood cell formation, mineral storage pool
2 bone mechanical properties
cable-like flexibility and resistance to tension, pillar-like stiffness and resistance to compression
structure of bone which allows cable-like flexibility and resistance to tension
framework is collagen and other bone proteins (osteoid)
structure of bone which allows pillar-like stiffness and resistance to compression
impregnation of collagen with crystalline mineral (hydroxyapatite - complex calcium hydroxyphosphate)
2 main types of bone tissue
woven (immature), lamellar (mature)
where is woven bone found in adults
earlier stages of repairing fractures
lamellar vs woven bone
lamellar has lamellar layers; woven is much more irregular
components of typical long bone, using femur as example
shaft (diaphysis), heads (epiphysis)
contents and components of bone in femur head, and femur shaft
femur head: proximal epiphysis, spongy bone, metaphysis, medullary cavity in diaphysis, compact bone (thicker and denser), articular cartilage on end at joint; shaft: nutrient foramen for nutrient artery, hollow medullary cavity for marrow and reduce mass
describe arrangement of lamellar bone
outer hard layer of compact lamellar bone (cortical bone), inner layer of interlacing struts of lamellar bone (cancellous / spongy / trabecular bone)
describe trabecular bone
lamellar but irregularly arranged
microscopy of lamellar bone
osteon (central canal with nerves and vessels, with concentric lamellae containing many osteocytes connected by gap junctions (share nutrients, get rid of waste), and calcium salt deposits)
rich blood supply of bones
major supply is from nutrient artery through nutrient foramen/canal; arteries at epiphysis also
what is the outer layer of bone called
periosteum
2 structural features of periosteum
fibrous and cellular
roles of periosteum
bone growth, repair
blood and nerve supply of periosteum
vascular and good sensory nerve supply
bone cell maturation pathway
osteogenic stem cell -> osteoblast -> osteocyte -> osteoclast
what do osteoblasts do
form bone matrix
what do osteocytes do
maintain bone tissue
what do osteoclasts do
function in resorption and breakdown of bone matrix (targeted to prevent bone loss)
describe border of osteoclasts
ruffled
when does the skeleton form in foetal life and when does growth of some bones continue until
starts at 6 weeks of foetal life, and can continue until 25 years of age
2 types of ossification
intramembranous, endochondral
where is intramembrous ossification
in existing vascular connective tissue
where is endochondral ossification
within existing foetal cartilage models
what happens in intramembrous ossification
bone matrix (ostein) deposited around collagen -> mineralises to form woven bone -> remodels to lamellar bone
what happens in endochondral ossification
cartilage calcifies and chondrocytes die -> periosteal osteoclasts cut channels for sprouting vessels -> osteoblasts enter with vessels to build bone round them
intramembrous ossification
development of ossification centre -> calcification -> formation of trabeculae -> development of periosteum
issue with long bones needing to support large forces while growing
would disrupt terminal appositional growth
solution to preventing disruption of appositional growth in long bones while growing and supporting large forces
shaft ossifies first, followed by epiphyses -> growth continues by ossification at growing cartilage plate between them -> growth cessation when cartilage growth ceases and plate is over-run by ossification
process of enochrondral ossification
development of cartilage model -> growth of cartilage model -> development of primary ossification centre (attracts osteoclasts) -> development of medullary (marrow) cavity -> development of secondary ossification centre -> formation of articular cartilage and epiphyseal plate
bone elongation: epiphyseal growth
chondrocyte-like cells arranged in columns; continuous proliferation and elongating shaft in one direction
age-related changes in appearance of normal bones: when do child’s wrist epiphyses ossify
2nd year (so anytime beforehand, gaps are epiphyseal plates not fractures)
age-related changes in appearance of normal bones: when do epiphyseal plates stop remaining cartilaginous
until growth ceases after puberty (so anytime beforehand, gaps are epiphyseal plates not fractures)
4 aspects of bone adaptability
can grow without compromising its support functions, increases or decreases bulk and density in response to pattern of use, can alter its external and internal shape in response to pattern of use (remodelling), can repair when fractured
3 keys to growth and remodelling of bone
bone has a large blood supply so cells are never far from nutrients and O2; osteocytes maintain matrix but can activate osteoblasts for new bone building; osteoclasts are giant cells specialised for destruction of bone matrix
name and location of process of bone growing in diameter
apposition (addition to exterior at periosteum)
how does bone diameter grow (apposition)
osteoblasts and osteoclasts create ridges and grooves on bone surface -> blood vessels align in grooves -> osteoblasts build new osteons round vessels -> osteoclasts remove bone from endosteal surface
9 fractures of bone
transverse, oblique, spiral, comminuted, segmental, avulsed, impacted, torus, greenstick
diagram of 9 fractures of bone
diagram
stages of fracture healing
haematoma -> new blood vessels -> bony callus of spongy bone trabecula -> healed fracture
what is an important part of fracture healing and why
bleeding, as haematoma becomes infiltrated by fibrous matrix and invaded by cartilage/bone progenitors
what bone tissue is fracture repair via
woven (immature healing bone) tissue, which then becomes lamellar bone
what does late fracture repair involve
reactive cartilage undergoing endochondrial ossification
what happens if blood [Ca2+] levels high
calcitonin released by parafollicular thyroid cells -> breakdown of bone matrix by osteoclast inhibitition, and uptake of Ca2+ into bone matrix is promoted
what happens if blood [Ca2+] levels low
parathyroid hormone (PTH) released by chief cells of parathyroid gland -> osteoclast bone resorption activity promoted, and increased Ca2+ reabsorption by the kidneys
