Session 5 - Kidney, calcium and renal stones

Question 1

What is the function of calcitriol?

Answer 1

Calcitriol increases Ca levels in blood by promoting absorption of Ca from intestine and reducing loss of calcium in kidneys.

Question 2

outline the process which occurs if serum calcium is low.

Answer 2

• Parathyroid gland secretes PTH
• PTH pulls calcium and phosphate from bones and into blood and tells kidneys to produce calcitriol from calcifediol (25-(OH) vit D).

PTH also increases calcium and magnesium reabsorption in the kidneys and decreases phosphate and bicarbonate reabsorption.

Low Ca –> PTH –> Calcifediol –> calcitriol

Question 3

Give 3 factors that can lead to stone formation

Answer 3

• Low urine pH
• Saturated levels of calcium oxalate in the urine
• Inadequate fluid intake or excessive fluid loss

Question 4

Describe the pathophysiology behind kidney stones

Answer 4

• Urine becomes supersaturated (urine contains more solutes than it can hold in solution) with calculogenic substances
• Through the process of nucleation, a crystal forms by adhering to a wall, and the seed crystal grows
• Unusually high or low pH affects the solubility of certain ions in urine, making it more or less likely to form a crystal.
• Normal urine contains chelating agents, e.g. citrate, that inhibit nucleation of crystals. Low levels of chelating agents = higher risk of renal stoness