Ossification Flashcards
What is endochondral ossification?
The replacement of a pre-existing hyaline cartilage template by bone. This is the way most bones of the body develop.
What are epiphyses?
The end parts of the bones; the last bit to ossify.
What are the diaphyses?
The middle parts of the bone that are the first bits to ossify.
How does growth of a bone occur?
More cartilage is formed and then this cartilage is ossified.
What are the steps of long bone formation?
initial cartilage model forms in embryo, collar of periosteal bone appears, central cartilage calcifies, arteries penetrate bone, primary ossification centre formed, medulla becomes cancellous bone, epiphyseal growth plates formed, epiphyses develop secondary ossification centres, epiphyses ossify and growth plates continue to move apart
- growth plates replaced by bone
What is intramembranous ossification for?
increase in bone girth
formation of flat bones
What are the zones of growing bone from outer to inner?
zone of reserve cartilage, zone of proliferation, zone of hypertrophy, zone of calcified cartilage, zone of resorption
What occurs in the zone of proliferation?
chondrocytes actively divide to produce columns and the cells enlarge and secrete matrix
What occurs in the zone of hypertrophy?
cells (chondrocytes) enlarge greatly and the matrix is compressed into linear bands
What occurs in the zone of calcified cartilage?
The enlarged chondrocytes begin to degenerate and the matrix calcifies
What occurs in the zone of resorption?
small blood vessels and connective tissue invade regions occupied by dying chondrocytes, calcified cartilage is left as spicules and bone is laid down on these spicules
Where does intramembranous ossification take place?
within condensations of mesenchymal tissue
Name some flat bones that develop by intramembranous ossification
skull, scapula, clavicle, pelvis
What is osteogenesis imperfecta?
An autosomal dominant group of genetic disorders of connective tissue. Caused by mutations in the gene for Type I collagen.
What are the signs of osteogenesis imperfecta?
blue sclerae (whites of eyes), fractured and callused bones, bowed tibia, bowed forearms, bone deformity, bone displacement at joints, thin and attenuated forearms
How does growth hormone cause gigantism?
excess of GH before puberty which promotes epiphyseal growth plate activity
What is the condition called when you have insufficient GH?
Pituitary dwarfism
Why can’t excess GH cause gigantism in adults and what does it cause?
cannot cause gigantism because there are no longer any epiphyseal growth plates instead it causes acromegaly by periosteal growth
How does early sexual maturity affect bones?
increased sex hormones retards bone growth because epiphyses close prematurely
What happens to bones if sex hormones are deficient?
prolonged bone growth so tall stature
How does hypothyroidism affect stature?
Short stature
What is osteoporosis?
A metabolic bone disorder in which mineralised bone is decreased in mass to the point it no longer provides adequate support, there is enhanced bone resorption and susceptibility to fracture.
What is Type 1 primary osteoporosis?
occurs in post-menopausal women with increased osteoclast activity due to decline in oestrogen
What is Type 2 primary osteoporosis?
occurs in elderly people and reflects diminished osteoblast function
What are the risk factors for osteoporosis?
genetics, calcium uptake, vitamin D, exercise and smoking
What is achondroplasia?
The most common form of short limb dwarfism, normal mental function and average lifespan. An autosomal dominant mutation that causes a gain of function of the FGFR3 gene and decreased endochondral ossification.
What is the action of vitamin D?
promotes bone resorption to release calcium and increases calcium uptake in gut
What is rickets?
A childhood disease where the bones don’t harden due to a deficiency in vitamin D. There is insufficient calcium deposition in the bone so they are soft and malformed.
What is osteomalacia?
The adult counterpart of rickets caused by significant calcium or vitamin D deficiency.
What are the signs of osteomalacia?
bone pain, back ache, muscle weakness
What are the most common fracture sites due to bone disorders?
femoral neck, pubic ramus, spine, ribs
What makes up 65% of bone?
hydroxyapatite crystals
