Calcium and Bone Tutorial Flashcards
what 2 substances make up most of bone?
calcium phosphate
collagen
which is the more dense of trabeclar and cortical bone?
cortical
what is the general weight of total body calcium?
1.5kg
what are the 3 main compartments of body calcium?
extracellular
intracellular
skeleton
what compartment contains plasma calcium?
extracellular
what secretes calcitonin?
parafollicular C cells in the thyroid gland
where are the enzymes located that activate Vitamin D?
liver
kidneys
what level of calcium in the body would trigger PTH?
(low) hypocalcaemia
main functions of PTH?
increase serum Ca
decrease serum phosphate
activate vitamin D in kidney
what kind of bone cell does PTH activate to cause resorption of bone and Ca?
osteoclast
what does PTH do to the kidneys to increase Ca and decrease phosphate?
makes them undergo tubular resorption
where is vitamin D synthesised?
intestine
main role of vitamin D?
increases kidney absorption
what 2 components make up vitamin D?
dehydrocholesterol from UV light
diet
when is the only time that calcitonin is secreted?
only in extreme hypercalcaemia
what is the main action of calcitonin?
decrease serum Ca
how does calcitonin decrease serum Ca?
inhibits osteoclasts to decrease bone resorption AND decreases tubular resorption
which substance has an opposing role to PTH?
calcitonin
what areas of the body are stimulated in hypercalcaemia?
smooth muscle
heart
nerves
ALL INCREASE
why do patients with hypercalcaemia get kidney stones?
increased levels of Ca in blood form stones with a high Ca content
why do you get arrhythmias in hypercalcaemia?
increased excitability of the heart due to increased serum Ca
why do patients get muscle weakness in hypercalcaemia?
although pts get stimulated smooth muscle, skeletal muscle is understimulated so they become weak
what GI complaint is common of hypercalcaemia patients?
constipation
what type of muscle is stimulated in hypocalcaemia? what are the symptoms of this
skeletal
tetany/cramp/pins and needles
why are patients more prone to osteoporosis in hyperparathyroidism?
PTH increases osteoclasts which break down bone
commonest cause of raised Ca?
primary hyperparathyroidism
3 findings needed for a diagnosis of primary hyperparathyroidism?
raised serum Ca
raised PTH
raised urine Ca excretion
most common cause of primary hyperparathyroidism?
adenoma of the parathyroid gland
management of hyperparathyroidism?
high fluid intake
low Ca/vit D diet
surgery of adenoma if serious symotoms
why do patients get hypoparathyroidism?
lack of cells secreting PTH
what is di george syndrome?
condition causing congenital absence of the parathyroid glands
how can autoimmune disease cause hypoparathyroidism?
destructs parafollicular cells
what is chvosteks sign?
twitching of the facial muscle when gentle tapping is applied to the facial nerve
what is trousseau’s sign?
inflated blood pressure cuff causes tetany of the muscles of the hand and wrist
why are hypoparathyroid patients still at a high fracture risk?
lack of bone remodelling due to low PTH
treatment for hypoparathyroidism?
calcium/vit d supplements
cause of pseudohypoparathyroidism?
genetic receptor abnormality leading to resistance of PTH
why are PTH levels high in pseudohypoparathyroidism?
more is made to try to gain a response
what hand abnormality is seen in pseudohypoparathyroidism?
blunting of digit 4
what 2 problems can stop vitamin D from being ACTIVATED and why?
liver/kidney failure as these are where the enzymes that activate it are
what happens to PTH levels when vitamin D is low?
will increase to maintain normal serum Ca
why can bone become soft?
low vitamin D causes lack of mineralisation of bone
how can you tell osteomalacia and rickets apart?
bone is NOT deformed
DO have a gait abnormality due to proximal myopathy
what does a T score in a DEXA scan compare?
bone mineral density to the mean result of a young adult female population
what does a Z score in a DEXA scan do?
mean bone mineral density compared to females of the same age
what BMD values indicate osteopenia?
> 1 but under 2.5 standard deviations below the young adult mean
what BMD values indicate osteoporosis?
> 2.5 standard deviations below the young adult mean
oily fish is rich in what vitamin?
D
what further investigations should be done into osteoporosis to figure out the cause?
bone biochem coeliac antibodies protein electrophoresis PTH levels testosterone
is weight bearing or non weight bearing exercise better for osteoporosis?
weight bearing (preserves bone density)
what do bisphosphonates do?
anti-resorptive ie they inhibit osteoclast activity
main bisphosphonate taken by patients?
alendronate
effect of an addisonian crisis on Na and K?
low Na
high K
what should always be in the differential for someone with tachycardia and hypotension?
sepsis
what 3 things are used to manage an addisonian crisis?
glucose
IV fluids
steroid replacement eg hydrocortisone
main iatrogenic cause of an addisonian crisis?
taking a patient immediately off a long term steroid course
when is the only time that a short synacthen test would be inaccurate?
immediately post acute pituitary apoplexy
what are sick day rules?
if the patient is ill one day they should double their dose for that day
why does a lesion in the pituitary stalk cause increased prolactin?
inhibits dopamine transmission from the hypothalamus
why would you experience postural hypotension in hypopituitarism?
lack of ACTH release stops mineralocorticoid (eg aldsterone) production
what would TFTs look like in someone with hypopituitarism?
low or normal TSH
low T4
why are T4 levels low in hypopituitarism?
lack of TSH from the pituitary
commonest cause of hypopituitarism?
pituitary tumour
infective causes of hypopituitarism?
meningitis
syphilis
encephalitis
treatment for hypopituitarism?
HRT eg thyroxine, steroids, testosterone
what is TRAB?
TSH receptor antibodies
