Limbs 1: Development & Growth of Bone Flashcards
Function of bone
Support of the body shape System of levers for muscle action Protection of internal organs Site of blood cell formation Mineral storage pool
What are the 2 mechanical properties of bone
Cable-like flexibility/resistance to TENSION
Pillar-like stiffness/resistance to COMPRESSION
What allows for cable-like flexibility in bone
collagen + other bone proteins (= osteoid)…. resistant to tension
What allows for pillar like stiffness in bone
by impregnation of collagen with crystalline mineral… allowing resistance to COMPRESSION
Which mineral is collage impregnated with in bone
(hydroxyapatite – a complex calcium hydroxyphosphate)… it’s crystalline
Types of bone tissue
Lamellar (=mature bone)
Woven (=immature bone)
T/f woven bone is commonly found in adult bone
F In adults woven bone is only found in repairing fractures… and pagets
What are the ends of bone called, and what is between this and the shaft
Ephiphysis (PROXIMAL= nearer to trunk, DISTAL=further)
metaphysis separates epiphysis from the shaft (diaphysis)
What is the name of the shaft
Diaphysis
What is the name of the hollow part inside bone
Medullary cavity
What is the name of the arteries that enter the epiphysis, metaphysis and diaphysis
Epi- eiphysial artery
Meta- metapyseal artery
Diaphysis - nutrient arteries which go through a nutrient foramen into the medullary cavity, then branch to supply the bone, and even back out to the periosteum
T/f periosteum is purely fibrous
F. it also is cellular
Role of periosteum
Key roles in bone growth and repair
Vascular
Sensory nerve supply is good
T/f periosteum is vascularised, but with poor sensory nerve supply
F… both vasuclarised and good sensory supply
What is an osteogenic cell
A cell which develops into an osteoblast (precurosr)
What is osteoblast a precursor to
osteocyte
What is the function of an osteoblast
forms bone marrix (i.e. secretes the collagen fibrils)
What is the function of osteocyte
Maintains bone tissue
T/F an osteocyte differentiates into an osteoclast
F, osteoblast forms osteocyte, but osteoclast separate
Function of osteoclast
Resoprtion (breakdown of bone matrix using lysosomal enzymes)… they have ruffled border
When does skeleton begin to form, when does growth stop
The skeleton starts to form at 6 weeks of fetal life and growth continues in some bones until 25 years of age.
How is lamellar bone arranged
CORTICAL (Outer hard layer of compact lamellar bone)
TRABECULAR/CANCELLOUS/SPONGY (Inner layer of interlacing struts of lamellar bone)
T/f spongy bone is woven as it is immature
FALSE!!! the spongy bone is lamellar…. woven is immature bone, which spongy bone is not
Structure of cortical bone
Osteon, the chief structural unit of compact (cortical) bone, consisting of concentric bone layers called lamellae, which surround a long hollow passageway, the Haversian canal. Made up of osteocytes with lots of processes
As well as instersitital lamellae
What is contained within the harvesian canal
neurovascular bundle
Structure of trabecular bone
Trabeculae are the spikes, and there are spaces between them which bone marrow fits into
Also in concentric circles but not called osteons…. it’s all interstital lameallae. No harvesian canals running inside. Osteoblasts are aligned along trabeulae of new bone (underneath is the osteocyte network)
State the 2 tpes of ossification and when each happens.. both in developng foetus
Intramembranous (in existing vascular connective tissue) –> FLAT BONES
endochondral (within existing foeatal cartilage models) –> OTHER BONES
In which type of ossification is ostein deposited around collagen
Intramembranous
What happens in intramembronous ossification
Mesenchymal stem cells within fibrous connective tissue (vascular connective tissue) differentiate into osteoblasts. These form ossification centres
Osteoid laid down (collagen). Osteoblasts which get trapped in the bone matrix called osteocytes
Mineralises to form spicules then trabeculae. This is woven bone
It then remodels further to form lamellar bone.
(note, there is still trabcular and cortical within this)
https://www.youtube.com/watch?v=xXgZap0AvL0
What happens in endochondral ossification
Within existing cartilage
There are chondrocytes which are secreting a matrix. Enclosed in a perichondrium.
Then hypertrophy of chondrocytes in the centre of the cartilage model. They resorb the surrounding matrix. The remaining cartilage matrix is calficied and the condrocytes die
Stem cells in the perichondrium divide to form osteoblasts.
Periosteal bud with capillaries and osteoblasts invade the calcified cartilage reason–> Primary ossification centre. PERIPHERAL OSTEOCLASTS CUT CHANNELS FOR SPROUTING VESSELS
Bone is built on the calficied cartilagte
Then later on, a secondary ossification centre forms in the epiphysis. This replaces calcified cartilage with mostly spongy bone.
Osteoclasts resorb bone in the diaphysis creating medullar cavity.
The gap between the primary and secondary ossification centres is the epiphyseal growth plate…. all future growth oiccutrs here
An area of cartilage remains over the epiphysis *=articular cartilage)
How does osteoblast get into foetal calcified cartilage
Periosteal osteoclasts cut channels for sprouting vessels
Osteoblasts enter with vessels to build bone round them
Stages of intramembranous ossification
osteoblasts secrete osteoid, which they becomeme trapped in forming ossification centre
Osteoblasts become osteocytes… as they do this, they cause osteogenic cells to convert into osteoblasts… so you get osteocytes in the cnetre and a ring of osteoblasts around outside. Calficiation occurs
Osteocytes in the centre become trabecular bone and cortical bone
The new osteoblasts on the outside become periosteum
Why is endochondral ossficiation needed
in children, there are large forces on the long bones, so you can’t really get frowth from the end of the bone (as it’s being compressed by force)….
What is the solution fo disruption of terminal appositional growth due to large forces on bone
- Shaft ossified
- Epiphysis ossifies
- The region in between the ossified shaft and epiphysis conitnues growing (growing cartilage plate)….
the bit in between ossified epiphysis and diaphysis is called epiphyseal plate… it keeps growing, and then then becomes calcified, grows some more, that bit gets calfified etc.
When will growth cessation occur
Growth cessation when cartilage growth ceases and plate is over-run by ossification
State stages of endochondral ossification
- Primary ossification centre forms in the shaft. Shaft becomes calcified. At this stage the eiphysis is still cartlage
- Secondary ossification centre forms in epiphysis, and ossification ocrrus here..
epiphyseal plate left in between
When does the child’s writst ossify
In child’s wrist (lower) epiphyses ossify in 2nd year
When do eiphyseal paltes remain until
Epiphyseal plates (dark) remain cartilaginous until growth ceases after puberty
What is the key to growth and remodelling in bones
large blood supply – 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
What is apposition
Apposition – addition to exterior at periosteum
How does apposition occur
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
Identify different fracture types
…
How do fractures heal
- Bleeding- haematoma is infiltrated with fibrous matrix and invaded by cartilage/bone progenitors
The haematoma is contained within the periosteum
What type of bone occurs in fracture repair
woven
What if high blood Ca2+ level (hypercalcaemia)
Calcitonin released by parafollicular thyroid cells; breakdown of bone matrix by osteoclasts inhibited; uptake of Ca2+ into bone matrix is promoted.
What if blood Ca2+ low
Parathyroid Hormone (PTH) released by chief cells of parathyroid gland; osteoclast bone resorption activity promoted; increases Ca2+ re-absorption by the kidneys.
Outline he adaptable features of bone
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
