Control of Mineral Metabolism Flashcards
Name three functions of calcium.
Bone mineralization
Second-messenger signaling
Voltage-gated channels
In low-calcium states, cells become _____________.
hyperexcitable (because the membrane potential is more depolarized with less calcium on the outer membrane)
Calcium is ___________ absorbed.
poorly (only about 50%)
What percent of blood calcium is free, bound to proteins, and bound to salts?
Free: 50%
Proteins: 40%
Salts: 10%
The ______________ process does not affect phosphate levels.
osteocytic-osteolytic
The ________________ process does release calcium.
osteoclastic
Of the 1 gram of calcium eaten per day, what percent is excreted in the feces and urine (after passing through the blood)?
Feces: 87.5%
Urine: 12.5%
Comparatively, the absorption of phosphate is __________.
much better; of the 1.4 grams eaten per day, about 1,100 mg is absorbed
Parathyroid hormone is released by ________________.
the chief cells of the parathyroid
Explain the paradox of parathyroid secretion.
Usually, calcium is needed for exocytosis of hormones, but in the case of PTH, low serum causes its release. The chief cells accomplish this by monitoring calcium levels. They have Gq sensors that are inactive when binding calcium, but when calcium drops and calcium departs, the sensor activates and causes PTH secretion.
What effect does PTH have?
It directly increases osteocytic dissolution of bone and indirectly increases osteoclastic dissolution of bone. Also, it increases calcium absorption from the bone.
Why does PTH cause phosphate wasting?
If you increase [Ca], then you need to decrease PO4 otherwise precipitates could form.
How does PTH increase calcium absorption?
It increases the conversion of vitamin D to the active form.
How much calcium is absorbed and secreted by the gut each day?
Absorbed: 500 mg
Secreted: 325 mg
You pee out about _________ mg of calcium per day.
175 mg
