Development and growth of bone Flashcards
What are some of the 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 two mechanical properties of bone and what is responsible for these properties?
Cable-like flexibility – and resistance to tension because the framework is collagen and other bone proteins (osteoid) Pillar-like stiffness – and resistance to compression conferred by impregnation of collagen with crystalline mineral (hydroxyapatite – a complex calcium hydroxyphosphate)
What are the two main types of bone tissue?
Woven (immature) Lamellar (mature)
When is woven bone found in adults?
It is 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?
Epiphysis
What type of bone is found around the outside of the bone?
Compact lamella bone (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 this cavity?
Trabecular/spongy bone (this is still lamellar bone)
What units is lamellar bone in the compact bone arranged into?
Osteons/Haversian Systems They have a central canal containing vessels and around the vessels you have concentric layers of bone maintained by concentrically arranged osteocytes
In what planes are these units arranged?
They are 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 two layers of the periosteum?
Fibrous Cellular
What are the main roles of the periosteum?
Bone growth and repair It is vascular It has a good sensory nerve supply
What do osteogenic cells give rise to?
Osteogenic cells Osteoblasts Osteocytes
What lineage do osteoclasts come from?
They are derived from the immune cell lineage – they are modified macrophages
At what point in fetal life does the skeleton start to develop?
6 weeks
What are the two types of ossification?
Intramembranous Endochondral
Describe intramembranous ossification.
Occurs within existing vascular connective tissue Bone matrix (ostein) is deposited around the collagen This mineralises to form woven bone It then remodels to form lamellar bone
Describe endochondral ossification.
Occurs within existing fetal cartilage models Cartilage calcifies and the chondrocytes die Periosteal osteoclasts cut channels for sprouting vessels Osteoblasts enter with the vessels to build bone around them
List some bones in which intramembranous ossification takes place.
Skull bones Jaw bones Part of the clavicle
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 the epiphyseal plates will calcify
What is the mechanism of appositional growth of bones?
Apposition – addition to exterior at periosteum 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
What is the problem and solution of long bone growth?
Most long bones must support large forces while growing
These would disrupt terminal appositional growth
Solution?
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
How can bone be remodelled?
Blood Ca2+ levels high:
Calcitonin released by parafollicular thyroid cells;
breakdown of bone matrix by osteoclasts inhibited;
uptake of Ca2+ into the bone matrix is promoted.
Blood Ca2+ levels low:
Parathyroid Hormone (PTH) released by chief cells of parathyroid gland;
Bind to receptors on osteoblasts (osteoclasts don’t have PTH receptors)
Osteoblasts release osteoclasts activating factor
osteoclast bone resorption activity promoted - more calcium released into the bloodstream
increases Ca2+ re-absorption by the kidneys.
How is a fracture healed?
- Bleeding is an important part of the process.
- If the bone is stable this heamatoma will become infiltrated by fibrous matrix and invaded by cartilage/bone progenitors and becomes cartilaginous to form a callus - a connective tissue structure
- callus forms spongy bone
- spongy bone remodelling
Woven bone forms first then becomes lamella bone
