| Kidney stones can cause a great deal of pain and | | | | the early collecting ducts, and even the ascending |
| may require surgical removal. A single stone the size | | | | loop of Henle to a certain extent. |
| of a grain of sand can cause such excruciating pain | | | | This mechanism maintains the amount of calcium in |
| already. There are several factors which could | | | | the body. If it were not for this effect of the |
| facilitate the formation of kidney stones and | | | | parathyroid hormone on the kidneys, there would be |
| hyperparathyroidism is one of them. But why is a | | | | constant loss of calcium through the urine. In time, |
| hormone concerned mainly with bones involved in the | | | | this would deplete both the extracellular fluids and the |
| formation of kidney stones? First, we must explore | | | | bone of such a mineral. |
| the functions of the parathyroid hormone itself. | | | | Formation of Kidney Stones in Hyperparathyroidism |
| The Parathyroid Hormone | | | | Some patients with mild hyperparathyroidism may |
| The parathyroid hormone increases calcium and | | | | show signs of bone disease but most of |
| phosphate absorption from the bone. It does this by | | | | hyperparathyroid patients have the tendency to |
| utilizing two mechanisms. One is a rapid phase in | | | | form kidney stones. This may be due to the fact |
| which the osteocytes are activated to pump calcium | | | | that the excess calcium and phosphate absorbed by |
| and phosphate ions from the bone fluid into the | | | | the intestines or mobilized from the bones under the |
| extracellular fluid. Another requires the activation of | | | | influence of parathyroid hormone must be excreted |
| cells called osteoclasts. Unlike the osteocytes, | | | | by way of the kidneys, causing an increase in the |
| parathyroid hormone does not directly exert its | | | | concentration of these substances in the urine. |
| influence on the osteoclasts. Instead a signal from | | | | Because of this, calcium phosphate crystals tend to |
| the activated osteocytes will further activate the | | | | form in the kidney, forming calcium phosphate stones. |
| osteoclasts to increase bone resorption activity. | | | | Calcium oxalate stones may also develop because |
| Furthermore, parathyroid hormone also increases | | | | even normal levels of oxalate will cause calcium |
| renal tubular reabsorption of calcium while it diminishes | | | | precipitation at high calcium levels. |
| phosphate reabsorption. It also increases the rate of | | | | Most renal stones are also only slightly soluble in |
| reabsorption of magnesium and hydrogen ions while it | | | | alkaline media. This is the reason why there is a |
| decreases the reabsorption of sodium, potassium, | | | | greater tendency for renal stones to form in alkaline |
| and amino acid ions in almost the same way it | | | | urine than in acidic urine. This is the logic behind the |
| affects phosphate. Calcium reabsorption is increased | | | | acidotic diets and acidic drugs frequently used to |
| mainly in the late distal tubules, the collecting tubules, | | | | treat renal calculi or kidney stones. |