Phosphocalcic Metabolism Flashcards
What is the main storage site for calcium in the body?
Bones (99%) in hydroxyapatite form.
A patient with tetany and carpopedal spasms has low calcium. What is the diagnosis?
Hypocalcemia, likely hypoparathyroidism.
What is the biologically active form of calcium in the blood?
Ionized calcium (Ca²⁺), 50% of total calcium.
What hormone increases calcium absorption in the intestine?
Vitamin D (Calcitriol, 1,25(OH)₂D₃).
What is the normal total serum calcium level?
What is the normal total serum calcium level? A: 90 – 110 mg/L.
What is the normal phosphate level in adults?
30 – 40 mg/L.
What hormone inhibits bone resorption and decreases
Calcitonin
A patient with chronic kidney disease has high phosphate levels. What is the cause?
Reduced renal excretion of phosphate.
What is the major cause of hypophosphatemia?
Hyperparathyroidism (increased renal phosphate excretion).
A patient with renal failure and hyperphosphatemia is at risk of what condition?
Secondary hyperparathyroidism.
What condition presents with bone pain, fractures, and high alkaline phosphatase?
Osteomalacia or Rickets.
What are the daily calcium requirements for adults?
1000 mg/day.
What sample is used for serum calcium measurement?
Serum or heparinized plasma (not EDTA or citrate).
What hormone is the main regulator of calcium homeostasis?
Parathyroid Hormone (PTH).
What is the function of FGF23 (Fibroblast Growth Factor 23)?
Increases renal phosphate excretion (hypophosphatemic effect).
A patient with muscle weakness and arrhythmia has low magnesium. What is the likely cause?
Hypomagnesemia due to renal loss or malabsorption.
What is the most sensitive method for ionized calcium measurement?
Ion-selective electrodes (ISE).
A patient with hypercalcemia and kidney stones likely has what condition?
Primary hyperparathyroidism.
How does chronic alcohol use affect magnesium levels?
Causes hypomagnesemia due to renal loss.
What is the primary site of calcium absorption in the intestine?
Duodenum.
A patient with low PTH, low calcium, and high phosphate presents with muscle spasms. What is the most likely diagnosis?
Hypoparathyroidism
What is the primary stimulus for PTH secretion?
Low calcium levels (hypocalcemia).
What is the role of PTH in the kidneys?
Increases calcium reabsorption and increases phosphate excretion.
A patient has osteolytic bone metastases. What electrolyte imbalance is expected?
Hypercalcemia due to bone resorption.
What are the three main hormones regulating calcium metabolism?
PTH, Vitamin D (Calcitriol), and Calcitonin.
What is the active form of Vitamin D, and where is it produced?
1,25(OH)₂D₃ (Calcitriol), produced in the kidneys.
What is the normal range for ionized calcium in the blood?
1.18 – 1.34 mmol/L.
What hormone inhibits bone resorption and is used to treat osteoporosis?
Calcitonin
A patient with kidney failure has hyperphosphatemia. What causes this?
Decreased renal phosphate excretion.
What electrolyte imbalance is common in chronic kidney disease (CKD)?
Hyperphosphatemia and hypocalcemia due to low Vitamin D activation.
A patient presents with bone pain, high PTH, and low phosphate. What is the likely diagnosis?
Primary hyperparathyroidism.
How does FGF23 (Fibroblast Growth Factor 23) regulate phosphate?
Increases renal phosphate excretion and inhibits Vitamin D activation.
What sample type is preferred for phosphate measurement?
Serum or heparinized plasma (avoid hemolyzed samples).
What test is used to adjust total calcium for albumin levels?
Corrected calcium formula: Total calcium + 0.8 × (4 – Albumin in g/dL).
A patient with tetany, prolonged QT interval, and low calcium is diagnosed with what condition?
Hypocalcemia (possible hypoparathyroidism or Vitamin D deficiency).
What condition presents with hypercalcemia, kidney stones, and bone pain?
Primary hyperparathyroidism.
What is the main route of magnesium elimination?
Renal excretion (90% reabsorbed in tubules, 10% excreted in urine).
A patient has muscle weakness, hypokalemia, and low magnesium. What could be the cause?
Chronic alcoholism or diuretic use (causing renal magnesium loss).
What is the main site of calcium absorption in the intestine?
Duodenum (via active transport regulated by Vitamin D).
