Flashcards in Control of Mineral Metabolism Deck (22):
Name three functions of calcium.
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?
The ______________ process does not affect phosphate levels.
The ________________ process does release calcium.
Of the 1 gram of calcium eaten per day, what percent is excreted in the feces and urine (after passing through the blood)?
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.
The intracellular [Ca] is about _____________.
True or false: phosphate is primarily excreted in the GI tract.
False. Of the 1,100 mg absorbed daily, about 900 mg is peed out and 200 mg is excreted in feces.
What three things does PTH do in the kidney?
- Stimulates Ca absorption
- Stimulates PO4 secretion
- Stimulates conversion of vitamin D
Which enzyme in the kidney activates vitamin D?
1-alpha hydroxylase ("#1 from where you go #1")
What happens to vitamin D if phosphate falls?
It is increasingly converted to the active form.
What are the symptoms of hypercalcemia?