Metabolic Bone Disease Flashcards
(43 cards)
What is the role of osteoclasts?
Bone resorption
What is the role of osteoblasts?
Bone formation
What happens when osteoblasts become encased in bone?
they become osteocytes
what type of cell is an osteoclast?
a macrophage
what does the whole cycle of bone biology aim to do?
bone remodelling
what is RANK?
RANK is the receptor for RANK-Ligand (RANKL) and part of the RANK/RANKL/OPG signaling pathway that regulates osteoclast differentiation and activation. It is associated with bone remodeling and repair, immune cell function, lymph node development, thermal regulation, and mammary gland development.
describe the factors that stimulate osteoblast expression of RANK Ligand?
Free Rank ligand joins on to a receptor on pre osetoclast on rank and the osteoclast then stimulated to multiply and divide and resorb bone and then this triggers the bone re-modelling cycle
OPG- and the RANKL balance, gives us how much free RANKL there is as OPG is a blocker of RANKL
Name 2 Vitamin D related disorders?
rickets and osteomalacia
Where can you get Vit D from?
diet and sunshine
dietary sources are poor; oily fish and egg yolk
cod liver oil capsules are a source of vitamin d supplement
you have to get the majority of it from the sun (radiation; UVB rays)
melanocytes compete for the UVB light; the darker the skin the more vitamin D you need for 7DHC to be activated
people in prison, muslims lack vitamin D
what is 7DHC?
7-Dehydrocholesterol is a zoosterol that functions in the serum as a cholesterol precursor, and is converted to vitamin D3 in the skin, therefore functioning as provitamin-D3
describe 7DHCs course:
7DHC protein bound circulates; goes to the liver; and is hydroxylated which produces the storage form of vitamin D (stored in liver, fat, muscle)
Describe vit D course:
SKIN : 7DHC
Liver: 25(OH) Vit D
Kidney: 1,25 (0H)2 Vit D
how do you test someones vitamin d?
By measuring their 25 (OH) Vit D
what form of vit d is physiologically active?
the form in the kidney
what does sun tan lotion do?
blocks vitamin D
what do you do if the livers and kidneys are not working?
if liver and kidneys don’t work then you have to give the physiologically active form of vitamin D
Give an example of a bone active hormone?
PTH (parathyroid hormone)
PTH comes from parathyroid gland
too much PTH gives osteoporosis and so does too little
PTH and Vit D work together to move calcium in and out of the blood/ cells
if calcium is up, Phosphate is down
What does Severe nutritional vitamin d OR Calcium deficiency cause?
it causes insufficient minerlisation and thus rickets in a growing child and osteomalacia in the adult when the epiphyseal lines are closed
what does vitamin d do normally?
vitamin D stimulates the absorption of calcium and phosphate from the gut and calcium and phosphate then become available for bone mineralisation
what happens to muscle function in low vitamin d states?
muscle function is also impaired in low vitamin d states
(if epiphyseal plates have fused; osteomalacia
if they haven’t fused, rickets
if you have low vitamin D levels, you wont absorb as much calcium to mineralise bones and if you dont have access to calcium, you still wont mineralise bones
there are vitamin d receptors in muscles)
Give some signs of rickets in children:
stunted growth
large forehead
odd curve to spine or back (kyphosis)
large abdomen
wide joints at elbow and wrist
wide bones
odd shaped legs (bendy legs)
wide ankles
(nobbly bits at the ends of ribs: rickety rosary)
Describe osetomalacia:
no bendy legs or impaired growth
patient tends to present with bone pain and muscle weakness
minor fractures; looser zones; only respond if you treat with calcium vitamin d
osteomalacia; struggle to get up the stairs
What is Paget’s disease of bone?
localised disorder of bone turnover
increased bone resorption followed by increased bone formation
leads to disorganised bone: bigger, less compact, more vascular and more susceptible to deformity and fracture
(most common metabolic bone disease in western world after osteoporosis
all the bars and plates in trabecular bone are going in different directions; disorganised bone
because bone turnover is increased; increased vascularity and thus more likelihood of a fracture)
does pagets disease have a genetic component?
Yes, a strong genetic component
15-30% are familial
Loci of SQSTMI
