Flashcards in Regulation of Calcium and Phosphate Metabolism Deck (104)
Percent distribution of calcium in:
Bones and teeth
ECF = 0.1%
Plasma = 0.5%
ICF = 1%
Bones and teeth = 99%
What forms of calcium exist in the blood?
Calcium exists in ionized form, bound to plasma proteins, or complexed in non-ionized form
Protein bound = 40%
Unfilterable = 60%
Of the unfilterable Ca, 10% is complexed to anions and 50% is ionized calcium
T/F: changes in plasma protein concentration alter the total Ca concentration in the opposite direction
False: changes in plasma protein concentration alter the total Ca concentration in the same direction as protein concentration
What are 3 ways of altering forms of Ca in the plasma?
Altering total Ca by changing plasma protein concentration (changes in same direction)
Altering ionized Ca by changing the fraction of Ca complexed with anions (changes anion concentration)
Altering ionized Ca by changing the fraction of Ca bound to proteins (albumin binds Ca and H)
If plasma [Pi] increases, the fraction of Ca that is complexed ________, thereby _______ ionized [Ca]
How does plasma [Ca] change in conditions of acidemia vs. alkalemia?
Acidemia = high plasma [Ca] — high plasma [H], albumin binds more H, thereby increasing Ca
Alkalemia = low plasma [Ca] — low plasma [H], albumin binds more Ca, thereby decreasing Ca
What effect does hypocalcemia have on neuromuscular excitability?
Increases it, because more Ca is inside the cells
May lead to hypocalcemic tetany/spasticity
What effect does hypercalcemia have on neuromuscular excitability?
Depresses it; threshold shifts away from resting membrane potential
What are the regulators of plasma levels of calcium, thus controlling neuromuscular excitability?
Primary hyperparathyroidism and malignancy are clinical conditions related to _____levels of serum Ca
Hypoparathyroidism, renal disease, and vit D deficiency are clinical conditions related to ___ serum Ca
What are the 3 coordinated organ systems primarily involved in Ca homeostasis?
What hormone is responsible for bone formation from body calcium pool
What hormones are responsible for bone resorption into body calcium pool?
What hormones inhibit Ca excretion from kidneys?
What hormone is responsible for absorption of calcium from the GI tract into the body calcium pooL?
About 1500 mg of Ca is taken in daily via the diet. The majority of this is excreted where?
Stool = 1300 mg
[200 mg excreted in urine]
Extracellular concentration of Pi is inversely correlated to that of _____.
Where is the majority of our phosphate stored?
85% in bone
[14% in cells, less than 1% serum]
What system primarily controls the fine tuning of phosphate levels?
[renal tubular reabsorption is inhibited by PTH; reabsorption depends on transport maximum]
What are the 4 classic regulators of phosphate metabolism?
Calcitriol regulation of phosphate metabolism
Calcitriol increases phosphorus resorption from bone and absorption from intestine
INCREASES Pi reabsorption in kidney
PTH regulation of phosphate metabolism
Phosphorus resorption directly from bone, and indirectly activates intestinal absorption through stimulation of calcitriol production
What endocrine factors directly or indirectly control NaPi cotransporter activity in the apical membrane?
What effect do insulin, GH, and thyroid hormone have on renal phosphate reabsorption?
What effect do calcitonin, glucocorticoids, and ANP have on renal phosphate reabsorption?
What effect does a gain of function mutation have in FGFR3?
Endocrine FGF derived from bone, regulated by phosphate and vitamin D levels, which in turn regulate phosphate homeostasis
3 renal effects of FGF 23
Directly downregulates NaPi transporters in kidney
Stimulates PTH to downregulate NaPi transporters in kidney
Decreases Calcitriol production in kidney