Rise in ionised calcium
Stimulus · Suppresses PTH Releases calcitonin
A rise in ionised calcium acts on the same calcium-sensing receptor, switching PTH secretion off and releasing calcitonin from thyroid C cells. Acting on the receptor in the thick ascending limb it also causes renal calcium loss and blunts the response to ADH.
Detail
- Suppresses
- PTH secretion and, over days, PTH gene transcription and gland growth; also renal 1-alpha-hydroxylase
- Releases
- Calcitonin from thyroid parafollicular C cells
- Renal effect
- Calcium-sensing receptor activation in the thick ascending limb reduces paracellular calcium reabsorption and antagonises ADH in the collecting duct: nephrogenic diabetes insipidus, polyuria and volume depletion
- Commonest causes
- Primary hyperparathyroidism (commonest in outpatients) and malignancy (commonest in inpatients) account for about 90%
When it goes wrong
Serum calcium above about 3.0 mmol/L
Stones, bones, abdominal moans and psychic groans: polyuria and thirst, renal colic, constipation, nausea, depression and confusion; the ECG shows a short QT interval
Hypercalcaemic crisis, calcium above 3.5 mmol/L
Rehydrate with intravenous 0.9% sodium chloride first, then give intravenous zoledronic acid or pamidronate; calcitonin gives rapid but short-lived control and a loop diuretic is added only once the patient is volume-replete
Practise this structure
2 questions in the bank tagged Ionised Calcium.
A 22-year-old woman is brought to the emergency department 30 minutes after an argument at home, breathing rapidly and deeply. She complains of tingling around…
Foundations · middle twist
A 22-year-old woman is brought to the emergency department after 30 minutes of rapid, deep breathing that began during an argument. She reports tingling around…
Foundations · middle twist