ToB - Bone Flashcards
What are the functions of bone?
Haemopoiesis
Support and protection
Mineral storage (calcium and phosphate)
What is the composition of bone?
65% hydroxyapatite crystals
23% type 1 collagen
10% water
2% other proteins
How do PTH and calcitriol affect bone?
They cause osteoblasts to release cytokines which stimulate the activity and differentiation of osteoclasts.
This means the bone is broken down more, releasing the Ca2+ required.
What are the steps in repairing a fracture?
1) . Haematoma formation and bone cells near haematoma die. Phagocytes and osteoclasts remove dead cells.
2) . Infiltration of new blood vessels means a procallus of granulation tissue forms, which converts into a fibrocartilagenous callus.
3) . Fibroblasts produce collagen to span break and some hyaline cartilage.
4) . Bony callus formed as endochondral ossification replaces hyaline cartilage with spongy bone, and intramembranous ossification creates new spongy bone.
5) . Remodelling converts some of the spongy bone into compact.
What occurs during bone remodelling?
A cutting cone forms, where the osteoclasts are at the front, secreting acid and lysosomal enzymes onto the bone to break it down. The osteoblasts follow behind in the resorption bays, and fill in the gap created.
What is intramembranous ossification?
Develops flat bones and contributes to the thickening of long bones.
A primary centre of ossification forms from mesenchymal tissue and mineral deposit radiates outwards from that point (the mesenchymal cells differentiate into osteoblasts and secrete matrix which is then mineralised.)
What is endochondral ossification?
A hyaline cartilage precursor is mineralised to form bone.
1) . Compact bone forms collar periosteal bone on the shaft.
2) . Central cartilage calcifies and a nutrient artery supply develops in diaphysis = aid to osteogenesis cells
3) . Medulla becomes spongy bone whilst cartilage calcifies to form the epiphysial growth plate with their own secondary ossification centres.
4) . Epiphyses ossify and growth plates move apart until epiphyseal plates calcify upon adulthood.
What are the 5 zones of the epiphyseal plate?
RPHCR
1) . Reserve cartilage - no cell proliferation or matrix production.
2) . Proliferation - chondrocytes divide and form a column, whilst secreting extra cellular matrix.
3) . Hypertrophy - chondrocytes enlarge, compressing the cartilage between them into columns,
4) . Calcified cartilage - chondrocytes degenerate
5) . Resorption - calcified matrix is in contact with marrow, so CT and blood vessels can invade where chndrocytes died = spicules.
What is the effect of growth hormone on bone?
Prepubertal, an excess will cause gigantism by promoting the activity of the epiphyseal plates. A deficiency will cause pituitary dwarfism.
In adulthood, no epiphyseal plates, so an excess will cause acromegaly by promoting periosteum growth.
What is the effect of thyroid hormone on the bones?
A deficiency will cause congenital neonatal hypothyroidism (also known as cretinism).
What is the effect of sex hormones on the bone?
Testosterone and oestrogen both influence the development of ossification centres.
If an excess occurs in childhood (e.g. Tumour) it fuses the epiphyses = retarded growth.
If there is a deficiency, the person often grows very tall due to epiphyseal plates persisting later into life.
What is osteogenesis imperfecta and its symptoms?
It is an autosomal dominant disorder due to a mutation in the gene for type 1 collagen.
Symptoms include thin, blue sclerae, disfigured and fragile bones and bad hearing due to the ossification of auditory bones.
What is osteoporosis?
This is where the osteoblasts don’t fill the resorption bays left by the osteoclasts, meaning the bone mass decreases due to demineralisation of the trabeculae and breakdown of the collagen framework.
What are the risk factors for osteoporosis?
1) . Old age as bone mass is decreasing already.
2) . Being female as oestrogen inhibits the work of osteoclasts whilst stimulating the osteoblasts. After the menopause, the fall in oestrogen means osteoclasts activity increases.
3) . Poor Ca2+ and Vitamin D in the diet means that the body begins to break down bone in order to release serum Ca2+ levels.
4) . Immobility as bone only remodels under stress, so if immobile, bone loss occurs.
5) . Long term steroid use, as these inhibit the action of osteoblasts.
6) . Hypogonadism because testosterone and oestrogen both act to maintain the bone, so if these aren’t present this doesn’t occur.
What is achondroplasia?
It is an autosomal dominant disorder which leads to a mutation in the fibroblast growth factor (central to CT).
Decreased endochondral ossification
Decreased proliferation and hypertrophy of chondrocytes in growth plate
Decreased cartilage matrix production
OVERALL SMALLER GROWTH PLATE AND IT CAN’T EXPAND DUE TO SEALING OFF OF MARROW = NO NUTRIENTS
