Development and growth of bone Flashcards
What are the 5 functions of bone?
Support of the body shape Systems 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 and what is responsible for these properties?
Cable-like flexibility + resistance to tension because the framework is collagen + osteoid
Pillar-like stiffness + resistance to compression conferred by impregnation of collagen with crystalline mineral (hydroxyapatite))
What are the 2 main types of bone tissue?
Woven (immature)
Lamellar (mature)
When is woven bone found in adults?
Only found in repairing fractures
What is the technical term for the shaft of a bone?
Diaphysis
What is the technical term for the head of a bone? What type of bone is found here?
Epiphysis
Spongy bone
What type of bone is found around the outside of the bone?
Compact (cortical) bone
What is the term given to the cavity within the bone?
Medullary cavity (contains bone marrow)
What type of bone is found within the medullary cavity?
Trabecular/ spongy/ cancellous bone (still lamellar)
What units are lamellar bone in the compact bone arranged into?
Osteons
Have a central canal containing vessels + around the vessels you have concentric layers of bone maintained by concentrically arranged osteocytes
In what planes are osteons arranged?
Usually organised along pressure planes
What provides the main blood supply to the bone marrow?
Nutrient artery (passing through the nutrient foramen)
What are the 2 layers of the periosteum?
Fibrous
Cellular
What are the main roles of the periosteum?
Bone growth + repair
Vascular
Good sensory nerve supply
What do osteogenic cells give rise to?
Osteogenic cells
Osteoblasts
Osteocytes
What lineage do osteoclasts come from?
Derived from immune cell lineage (modified macrophages)
At what point in fetal life does the skeleton start to develop?
6 weeks
What are the 2 types of ossification?
Intramembranous
Endochondral
Describe intramembranous ossification.
Occurs within existing vascular connective tissue
Bone matrix is deposited around the collagen
This mineralises to form woven bone
Then remodels to form lamellar bone
Describe endochondral ossification.
Occurs within existing fetal cartilage models
Cartilage calcifies + chondrocytes die
Periosteal osteoclasts cut channels for sprouting vessels
Osteoblasts enter with vessels to build bone around them
Name 2 bones in which intramembranous ossification takes place.
Skull
Mandible
(Flat bones)
At what point do the epiphyses ossify in a child’s wrist?
2 years
Until what point do epiphyseal plates remain cartilaginous?
Until you stop growing: then epiphyseal plates will calcify
How does bone grow in length without disrupting terminal appositional growth?
Shaft ossifies 1st, followed by epiphyses
Growth continues by ossification at growing cartilage plate between them
Growth cessation when cartilage growth ceases + plate is over-run by ossification
Why is bone described as adaptable?
Can grow without compromising its support function
Increases/ decreases bulk + density in response to pattern of use
Can alter its external + internal shape in response to pattern of use (remodelling)
Can repair when fractured
Describe 3 features of bone that allow for remodelling
Bone has a large blood supply- cells never far from nutrients + O2
Osteocytes maintain matrix but can activate osteoblasts for new bone building
Osteoclasts are giant cells specialised for destruction of bone matrix
What is the name of growth in bone diameter? Describe this
Apposition: addition to exterior at periosteum
Osteoblasts + osteoclasts create ridges + grooves on surface
Blood vessels align in grooves
Osteoblasts build new osteons round vessels
Osteoclasts remove bone from endosteal surface
What is essential for intiating repair of a fracture?
Haematoma
Becomes infiltrated by fibrous matrix + invaded by cartilage/ bone progenitors
Describe the response to high blood calcium levels
Calcitonin released by parafolicular thyroid cells
Breakdown of bone matrix by osteoclasts INHIBITED
Uptake of Ca2+ into bone STIMULATED
Describe the response to low blood calcium levels
PTH released by chief cells of parathyroid gland
Osteoclasts bone resorption activity STIMULATED
Increases Ca2+ re-absorption by kidneys
