block 5 lecture 5 bone metabolism Flashcards
what percentage is organic bone material?
40%
what percentage is inorganic bone material?
60%
what is the organic materials of bone?
type 1 collagen and non-collagenous protein
what is the inorganic portion of bone?
calcium hydroxyapatite
what is trabecula bone?
cancllous and spongy bone
what are osteoclasts?
multi nucleated cells formed from many monocytes
what can increase the resorption of bone by an osteoclast?
bigger osteoclasts perform more aggressive resorption of bone
how do osteoclasts adhere to the bone matrix?
by forming lipid like adhesions and express strong intergrin interactions
what do osteoclasts do?
secrete enzymes and acids to degrade matrix
what happens to degraded bone material by osteoclasts?
shoots up through apical membrane and removed from the cell
what are the osteoclast resorption pits called?
howships lacuna
what are osteoblats?
mononucleated stromal cells
what do osteoblasts come from?
mesenchymal cells
what do osteoblasts do?
mineralize bone matrix to replace removed bone
what do osteoblasts form into?
osteocytes
what do the extesions of osteocytes make connections with?
the bones surface and other osteocytes
what do the processes of osteocytes act as?
mechnosensors
hat stops osteoclasts resorbing?
reversal stage
what is the matrix that osteoblasts lay down?
type 1 collagen and non colagenous protein
what is the bone matrix called when it is initially laid down?
osteoid
what are some signals involved in bone growth?
parathyroid hormine, vitamin D, calcitonin, growth hormone, growth factors, oestrogen, cytokines
what is the calcuim resevoir?
skeleton
what are the three fractions of calcium in serum?
ionised calcium, protein bound calcium and complexed calcium
what is Ca2+ maintained by?
PTH, Vitamin D, cacitonin
where do you find phsphate?
skeleton and extracellular fluid
what are the three fractions of phsophate in serum/
ionised phosphate
protein bound phophate and complexed
what is phsphate metabolism regulated by?
PTH
where can you recieve vitamin D?
in the skin, digestion
in the skin how is vitamin D procuced?
7-dehydrocholesterol is converted by UV light to vitamin D
how is vitamin D activated?
2 rounds of hydroxylation
where does the first hydroxylation of vitamin D occur?
liver
where does the second hydroxylation of vitamin D occur?
kidney
what type of vitamin D is responsible for most biological mechanisms?
principle hormonal form
what is the production of vitamin D regulated by?
PTH
what is the production of vitamin D inhibited by?
elevated serum calcium or phosphate
what doe vitamin D do?
increases calcium and phosphate absorption from intestines
mobilised calcium and phophate from bone
induces marrow monocytes to increase production of osteoclasts to promote resorption
what seceretes PTH?
parathyroid gland
what can PTH stimulate?
osteoclast resroption
decresases renal calcium secretion
increases renal production of vitamin D
what is parathyroid hormone related protein produced by?
normal and malignant cells
what is PTHrP required for?
development, regulator of proliferation and mineralisation of chondrocytes
what s calcitonin?
small poly peptide
what releases calcitonin?
parafollicular cells of the thyroid
what induces the release of calcitonin?
high plasma calcium levels
what does calcitonin do?
reduces bone resorption by activating calcitonin receptors expressed by osteoclasts
physiology of calcium metabolism to increase?
low calcium in circulation is detected by parathyroid gland, PTH is secreted, PTH and vitamin D increases the mobilisation of Ca into circulation
physiology of calcium metabolism to decrease?
calcium is detected by thyroid C cells, which increases the secretion of calcitonin, which targets osteoclats to limit resrption and decrease calcium in circulation
how does oestrogen affect bone metabolism?
reduce resorption by inhibiting osteoclastogenesis and inhibiting osteoclast function
how does androgens affect bone metabolism?
low levels means low bone density in men
they target osteoclasts
what are the causes of hypercalcium?
primary hyperthyroidism, malignancy, immobalisation, vitamin D toxicity
what is primary hyperthyroidism?
excessive secretion of PTH
what causes primary hyperthyroidism?
solitary adenoma of parathyroid glands
what are the symptoms of primary hyperthyroidism?
excessive skeletal erosion, kidney stones
causes of hypocalcemia?
renal failure, vitamin D defficiency, prematurity (immture vitamin D metabolism, immature parathyroid gland)
what is osteomalacia caused by?
vit D defficiency, malabsorption, renal disease, lack of sunlight, anticonvulsants inhibit vitamin D synthesis
osteomalacia symptoms?
bone pain around hips, muscle weakness, alavated alkaline phosphatase levels, decreased mineralisation, long bones bowing
what is osteoporosis?
net loss of bone mass and decreasd bone mineral density
in what type of person is osteoporosis common?
post menopausal woman, elderly, inactive
treatment of osteoporosis?
calcium supplementation, hormone replacement therapy, bisphosphates, calcitonin, selective estrogen receptor modulators
