Calcium Dysregulation Flashcards
what causes an increase in serum calcium?
vitamin d and parathyroid hormone
which hormone causes a decrease in serum calcium?
Calcitonin released by thyroid parafolliculae cells
what are the body’s sources of each of these?
- vitamin dsynthesised in skin or absorbed from diet
- parathyroid hormoneparathyroid glands
- calcitoninthyroid parafollicular cells
vit D3 skin metabolism pathway?
7-dehydrocholesterol + UVB → pre-vitamin D3 → vit D3 (inactive form)
what form of vitamin D is absorbed from the gut?
Vitamin d2
how are these inactive forms converted to active forms?
vit D3 → 25(OH)cholecalciferol → 1, 25(OH)2-cholecalciferol
Which enzymes convert vitamin D
25-hydroxylase in liver and 1-alpha-hydroxylase in kidney
what is the active form of vit D?
Calcitriol
how is its production from vit D3 regulated?
calcitriol decreases transcription of 1-alpha-hydroxylase
effects of calcitriol?
increased osteoblast activity
more gut Ca2+ and phosphate absorption
more kidney Ca2+ and PO34- reabsorption
effects of parathyroid hormone?
more Ca2+ resorption from bones (osteoclast)
more 1-alpha-hydroxylase activity → more Ca2+ and phosphate absorption from gut
more Ca2+ reabsorption from kidney, more phosphate excretion
how is serum phosphate regulated?
by FGF23 → downregulates calcitriol so less phosphate reabsorption through sodium phosphate co transporter
PTH a,so inhibits via fgf23
symptoms of hypocalcaemia?
paraesthesia, convulsions, arrhythmias, tetany
- chvostek’s signtwitch in facial muscle when gently tapping patient’s cheek
- trousseau’s signcarpopedal spasm on ischaemia (blood pressure cuff)
Causes of hypocalcaemia
- low PTH level → hypoparathyroidismsurgicalautoimmunemagnesium deficiencycongenital (rare)
- low vit D leveldeficiency (poor diet, UV light exposure, renal failure → impaired production)
symptoms of hypercalcaemia?
atonal muscles (reduced excitability)
stones, moans and abdomen groans
→ kidney stones
fatigue, depression, impaired concentration, coma at extreme high (above 3 mmol/L)
anorexia, nausea, dyspepsia, constipation, pancreatitis
Causes of hypercalcaemia
- primary hyperparathyroidismusually parathyroid gland adenoma
- malignancybony metastases produce local factors overactivating osteoclastssome cancers secrete PTH-related peptide
- vit D excess (rare)diet
primary vs secondary hyperparathyroidism (Ca2+ level)?
primary has high Ca2+ and high PTH
secondary has low Ca2+ and high PTH
primary vs secondary hyperparathyroidism (cause)?
primary = parathyroid adenoma independently producing too much PTH. Calcium increases but no negative feedback to suppress autonomous PTH
secondary = normal response to low serum Ca2+ e.g. vit D deficiency (diet, UV, renal failure)
treatment for primary hyperparathyroidism?
parathyroidectomy
treatment for secondary hyperparathyroidism?
Vitamin D replacement
Patients with normal Rena, function give 25 hydroxy vitamin D so pt makes calcitriol
(Vitamin D 2 is ergocalciferol and D3 is cholecalciferol)
In renal failure there isn’t enough 1 alpha hydroxylase so give alfacalcidol
cause of tertiary hyperparathyroidism?
chronic renal failure → chronic vit D deficiency → low Ca2+ thus high PTH
Pathology of tertiary hyperparathyroidism
long time overactive parathyroid gland → PTH up and Ca2+ up
involves hyperplasia
Occurs in chronic renal failure
Treat with parathyroidectimy
Normal PTH response to hypercalcaemia
pth falls
management of hypercalcaemia of malignancy?
bisphosphonates → osteoclast activity inhibitors
PTH wouldn’t be raised but calcium would
Untreated hyperparathyroidism
Increases risk of osteoporosis
Renal calculi
Mental function and mood
