calcium dysregulation Flashcards
what hormones are responsible for calcium and phosphate regulation
vit d
parathyroid hormone
calcitonin
what hormones increase serum calcium and phosphate
vit d - synthesised in skin
Pth - secreted by parathyroid glands - main regulators of homeostasis via actions on kidney, bone and gut
what hormone decreases serum calcium and phosphate
calcitonin - secreted by parafollicular cells
- reduce ca acutely
no neg effect if cells removed e.g in thyroidectomy
how do we replenish vit d in our bodies
main way is via sunshine
and diet
what are the first 3 steps in vit d synthesis
uvb absorbed by skin
7 dehydrocholesterol converted into pre vit d3
pre vit d converted into vit d3 in skin
travels in blood
what are the two essential hydroxylation steps in vit d synthesis
25 hydroxylase in liver to make 25(oh)cholecalciferol
1 alpha hydroxylase in kidney - becomes 1,25 oh2 cholecalciferol
what do we call the active form of vit d
calcitriol
what is a good indicator of body vit d status
serum oh vitamin d
how does calcitriol regulate its own synthesis
decreases transcription of 1 alpha hydroxylase
what are the effects of calcitriol on the bone
increases osteoblast activity - bone formation
what are the effects of calcitriol on the kidneys
increased calcium and phosphate reabsorption
what are the effects of calcitriol on the gut
increased calcium and phosphate absorption
what are the effects of pth on bone
increase calcium resorption from bone - osteoclast activity
what are the effects of pth on the kidneys
increased calcium reabsorption
increased phosphate excretion
increase production of 1 alpha hydroxylase activity
what is the effect of pth causing increase of 1 alpha hydroxylase activity
synthesis of calcitriol which acts on gut increasing calcium and phosphate absorption in gut
what is the main focus of parathyroid hormone
increase plasma calcium
through its actions on bone and kidney
and indirect action on gut
what is the hormone fgf23 made by ?
osteocytes
what is role of fgf23
regulate phosphate levels
what can high levels of fgf23 cause
low levels of phosphate
what does fgf23 do to in proximal convoluted tubule
inhibits sodium phosphate co transporter
forces phosphate not to be reabsorbed
what is another action of fgf 23
it inhibits calcitriol formation - leading to less phosphate reabsorption from gut.
what does hypocalcaemia cause
it sensitises excitable tissues - causing muscle cramps tetany and tingling(parathesia).
what are the signs and symptoms go hypocalcaemia
parathesia convulsions arrythmias tetany CATS go numb
what are two signs we can look out for in hypocalcaemia
chvosteks sign - facial parathesia
trosseaus sign - carpopedal spasm
how do we check for chvosteks sign
tap zygomatic arch for facial nerve
contraction on that side of neck
how to check for trosseaus sign
tight blood pressure cuff
arm contracts and can’t relax
what are the causes of hypocalcaemia related to low pth
= hypoparathyroidism could be from neck surgery autoimmune magnesium deficiency (needed for pth secretions) congenital - agenesis , rare
what are the causes of hypocalcaemia related to low vit d
deficiency - diet, uv light, malabsorption, impaired production - renal failure (1 alpha hydroxylation)
what does hypercalcaemia cause
reduced neuronal excitability - atonal muscles
why - calcium blocks sodium channels preventing action
effects of hypercalcaemia on kidneys
renal effects - kidney stones
renal colic
what are the effects of hyper cal on gi
gi effects - anorexia nausea dyspepsia constipation pancreatitis
what are the effects of HYPERCALCAEMIA on the cns
cons effects - fatigue depression impaired concentration impaired mentation coma if >3mmol/l
what is a way to remember symptoms of hypercalcaemia
stones, abdominal moans, psychic groans
what is the most common cause of hypercalcaemia
primary hyperparathyroidism - too much pth
-usually due to parathyroid gland adenoma
not sensitive to neg feedback therefore high pth and high calcium
what are some other causes of hypercalcaemia
malignancies- bony metastases produce local factors to activate osteoclasts
certain cancers secrete pth related peptide that acts on pth receptors
vit d excess e.g vit d supplements
biochem of primary hyperparathyroidism
high calcium
low phosphate - increased renal excretion
high pth
what is the treatment of primary hyperparathy…
parathyroidectomy
risks of untreated hyperparathyroidism
osteoporosis
stones
psychological impact
what is secondary hyperparathyroidism
calcium is low!!
normal physiological response to low calcium
causes of secondary hyperparathyroidism
vit d deficiency diet, reduced sunlight
less common - renal failure
treatment of secondary hyperparathyroidism
vit d replacement
ergocalciferol - d2
cholecalciferol - d3
if have renal failure - alfacalcidol - active version
what is tertiary hyperparathyroidism
chronic renal failure rare
cannot make vit d for long period of time
glands cells hyperplasia to compensate
cells can’t switched off
treatment for tertiary hyper-parathy…
parathyroidectomy
