Endocrine - Calcium and Parathyroid Flashcards
How does alkalaosis and acidosis impact calcium levels?
Alkalosis –> increases protein binding so LOWERS FREE Ca
Acidosis –> decreases protein binding so INCREASES FREE Ca
How is PTH secreted?
Decreased serum Ca is detected by CALCIUM SENSING RECEPTOR (CaSR) of parathyroid cells.
PTH is then secreted by CHIEF CELLS
Action of PTH?
1) Increased Ca reabsorption in the DISTAL TUBULE
2) Decreased phosphate reabsorption in PCT
3) Increased bone resorption
4) Stimulates 1alpha-hydroxylase in PCT which converts 25-OHvitD in liver to active 1,25-vitD in kidney
How does PTH increase bone resorption?
Binds to PTH receptor on osteoblasts to increase their RANK-L expression
Therefore increases osteoclat action
** intermittent pulsed PTH stimulates osteoBLAST activity
What does intermittent pulsed PTH do specially?
intermittent pulsed PTH stimulates osteoBLAST activity
How is calcitonin secreted and what does it do?
Calcitonin is secreted in response to ELEVATED free Ca by the PARAFOLLICULAR CELLS (C cells)
Decreases activity of osteoclasts
Causes of hypercalcaemia?
PTH-Dependent:
- primary hyperparathyroidism
- lithium
- familial hypocalciuric hypercalcaemia
MALIGNANCY
VITAMIN D RELATED
- Vit D intoxication
- Elevated 1,25(OH) vit D in
1) sarcoidosis / granulomatous disease (TB and histoplasmosis)
2) Impaired metabolism due to 24-hydroxylase deficiency
HIGH BONE TURNOVER RELATED
- hyperthyroidism
- immobilisation
- thiazides
- vit A intoxication
- fat necrosis
RENAL FAILURE RELATED
- severe secondary hyperparathyroidism
- aluminium intoxication
- milk-alkali syndrome
Causes of Vitamin D related hypercalcaemia
- Vit D intoxication
- Elevated 1,25(OH) vit D in
1) sarcoidosis / granulomatous disease (TB and histoplasmosis)
2) Impaired metabolism due to 24-hydroxylase deficiency
Causes of hypercalcaemia from high bone turnover
- hyperthyroidism
- immobilisation
- thiazides
- vit A intoxication
- fat necrosis
Types of hypercalcaemia causes associated with malignancy?
OSTEOLYTIC:
- commonly bone mets (breast / MM / lymphoma)
HUMORAL:
PTHrP from SCC, renal, overian, breast and endometrial
1,25(OH)vit D: lymphoma
Skeletal features of hyperparathyroidism
- Low BMD
- Fracture
- Osteitis fibrosa cystica
- Brown tumour
- Subperiosteal resorption of phalanges
- Tapering of distal clavicles
- Salt & pepper skull
Features of primary hyperparathyroidsim that suggest an underlying genetic cause?
- young <40yrs
- > 1 gland affected
- features of syndromic disease
- -> pituitary / pancreatic
- -> jaw tumour in parafibromin
- family history
Benefits of parathyroid surgery for primary hyperparathyroidsim?
Improved BMD and hip and lumbar spine
Improved QoL
Improved symptoms
Decreased risk kidney stones
Improved BMD
Reduced fracture risk
