Endocrine Control of Bone Health Flashcards
Define each of the following:
diaphysis
epiphysis
periosteum
endosteum
Diaphysis: shaft of bone
Epiphysis: end of bone
Periosteum: covers outside of compact bone
Endosteum: inside of bone
What % of bone is organic and what does this include?
35% of bone is organic, mostly osteoid matrix (collagen and calcium binding proteins) and bone cells
What is the benefit of collagen in osteoid?
Provides flexibility and tensile strength to bone
What % of bone is inorganic and what does this include?
65% inorganic, made of mineral salts, calcium phosphate and other minerals
What do inorganic minerals in bone privde?
bone hardness
Differentiate between the two types of bone ossification.
Intramembranous ossification where bone is created from fibrous membranes, skill, mandible and clavicle made this way
Endochondral ossification where bone replaces hyaline cartilage, most bones made this way
List the 5 main steps of endochondral ossification.
1) bone collar forms around diaphysis of cartilage
2) cartilage calcifies in centre of diaphysis
3) periosteal bud invades cavities within diaphysis calcification
4) diaphysis elongates, medullary cavity forms, secondary ossification centres appear in epiphyses
5) epiphyses ossify
Where is the only place cartilage is left after endochondral ossification and what does this allow?
between first and second ossification centres, allows elongation to occur
Formation of bone and remodelling is strongly influenced by which 2 molecules?
vitamin D and PTH
describe the role of: osteoblast, osteoclast and osteocyte
osteoblast- builds bone by secreting osteoid
osteoclasts- clear away bone to release calcium and other minerals
osteocyte- mature osteoblast that resides in bone matrix for many years monitoring and modifying bone properties
Describe the 4 main steps of intramembranous ossification
1) ossification centres develop in fibrous connective tissue membrane
2) osteoid secreted and calcifies
3) immature spongy bone and periosteum form
4) compact bone replaces immature spongy bone, just deep to periosteum, red marrow develops
What % skeleton replaced /year?
10%
How often is spongy bone replaced compared to compact?
spongy bone every 3 years, compact bone every 10 years
List the two main reasons for bone remodelling.
1) longer calcium stays in bone, more brittle it becomes, constant turnover=strong bone
2) bones are major calcium store in body, calcium released when required
Explain PTH relationship with bone remodelling
Decreased calcium levels in blood cause increase in PTH which stimulates release of RANK-L from osteoblasts and decrease release of osteoprotegrin, this triggers formation of new osteoclasts and increases activity of existing = resorbs bone and releases calcium into blood
Explain Vitamin D relationship to bone remodelling.
Acts on small intestine to increase calcium absorption, decreases kidney excretion of calcium, stimulates RANK-L release and decreases synthesis of osetoprotegerin
Explain relationship between PTH and vitamin D
PTH helps produce vitamin D
Why do osteocytes secrete osetoprotegerin?
To bind to RANK-L to inhibit activation of osetoclasts
Which hormones increase osteoprotegerin?
TH, estrogen, GH
Explain 4 main steps of repair of a fracture
1) haematoma forms
2) fibrocartilaginous callus forms
3) bony callus forms
4) bone remodelling occurs
Define osteomalacia
Group of bone disorders where osteoid is produced but minerals not stored adequately
Describe Rickets
Rickets is childhood form of osteomalacia leading to poor mineralisation in growth plates and bowed legs, caused by insufficient calcium or vitamin D
Describe osteoporosis
Group of disorders where bone resorption outpaces bone deposition, matrix remains normal but bone mass declines
Why is osteoporosis associated with postmenopausal women?
Estrogen promotes osteoblast function therefore after menopause estrogen levels drop decreasing function of osteoblasts. Additionally, estrogen increases OPG levels therefore without this increase there is more free RANK-L to activate osteoclasts
Which hormones stimulate RANK-L?
IGF, PTH, vitamin D, glucocorticoids
