Calcium and Phosphate Metabolism Flashcards
What are the most important hormones in calcium metabolism?
Ca2+
Parathyroid hormone
1,25(OH)2D (calciferol)
What are the most important organs for Ca2+ metabolism?
- Intestine
- Bone
- Kidney
- Parathyroid gland
Parathyroid hormone is produced in the ____ cells of the parathyroid gland
Chief
What are the two negative feedback loops that influence parathyroid hormone secretion?
- Serum ionized calcium
- Serum 1,25 dihydroxyvitamin D
How is renal tubular calcium handling regulated?
CaR
What is the best indicator of vitamin D status?
Calcidiol
What is the role of parathyroid hormone-related peptide (PTHrP) ?
Paracrine regulator of breast, skin and bone development
What is the most common cause of cancer-associated hypercalcaemia?
PTHrP production by tumours
Diagnosis of PTH dependent hypercalcemia requires ____ Ca2+ and ___ PTH
Elevated Ca2+
Increased PTH
Diagnosis of PTH independent hypercalcemia requires ____ Ca2+ and ___ PTH
Elevated Ca2+
Decreased PTH
How can cancer cause PTH independent hypercalcemia?
- PTHrP
- Extensive lytic bone disease
- Tumoral expression of 1-alpha hydroxylase -> 1,25 dihydroxyvitaminD
Why can sarcoidosis cause PTH independent hypercalcemia?
Granulomatous tissue can convert 25(OH)D -> 1,25(OH)2D
What is the most common cause of hypoparathyroidism?
Post surgical/post neck irradiation
What are the two most common abnormalities of vitamin D metabolism?
Vitamin D deficiency and renal failure
What are the main hormones involved in phosphate metabolism?
Vitamin D, PTH and phosphatonins
PTH ____ renal excretion of phosphate
Stimulates
Calcitrol ____ intestinal absorption of phosphate and _____ urinary phosphate excretion
Increases
Decreases
Phosphatonins _____ urinary phosphate secretion
Increase
What is the most important phosphatonin in phosphate regulation?
FGF-23
Why do very sick patients often have moderately low phosphates?
Respiratory alkalosis changes pH -> causes movement of phosphate from ECF to ICF
What is the main source of phosphatonins in the body?
Skeleton
What is the mechanism of FGF23?
- Inhibit production of phosphate transporting proteins in the renal tubule
- Inhibit 1-alpha hydroxylase enzyme
What is the mechanism of Fanconi syndrome?
Global deficiency in phosphate transport -> hypophosphatemia
