Glossary of 3. Calcium, Phosphorus, Magnesium

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Where is most of the body's calcium? Where is the least?
Most = skeleton
Least = ionized
What are 5 functions of Ca?
1. Muscle contraction
2. Bone mineralization
3. Coagulation
4. MEmbrane potential
5. Enzyme cofactor
Calcium is measured in what forms?
1. Total
2. Free
What are 2 methods for total Ca measurement?
-Atomic absorption spectrometry
Name 2 different photometric methods for calcium:
1. O-cresolphthalein complexone
2. Arsenazo III
-What color does the O-cresolph complexone reaction produce?
-At what pH?
-What else has to be done?
Red color
pH = 10-12
Remove Mg
-Competes with 8-hydroxyquinolone.
What wavelength is atomic absorption Ca method done at?
What needs to be done for the method?
-422.7 nm
-Remove Ca from protein w/ acid.
-Remove phosphate w. lanthanum.
What method is used to measure ionized calcium?
Ion-selective electrode.
What is the reference range of:
-Total calcium?
-Ionized calcium?
Total: 2.2-2.6 mmol/L

Ionized: 1.0-1.2 mmol/L
What specimens can be used for calcium measurements?
Serum or heparin whole blood
What can't be used?
Citrate, oxalate, EDTA
What should be done to specimens intended for Ca measurement?
Remove RBCs right away to prevent Calcium uptake.
What can alter calcium measurements horribly?
Gross hemolysis.
What physiologic measurement needs to be minded in Ca msmt?
pH; acid pH means more H+ will be on albumin, displacing Ca and increasing the free Ca+ measurement. Vice versa.
Name four functions of phosphate:
1. Hydroxyapetite
3. Phospholipid bilayers
4. Cellular buffering
what method is primarily used for measuring phosphate?
Photometric: phosphomolybdate
What specimen specifications apply to phosphate measurement?
same as for calcium.
What is the ref range for phosphate?
0.8-1.6 mMol
What is Magnesium's main function?
As an enzyme cofactor and activator.
List three methods for Mg measurement:
1. Photometric - dye binding
2. AAS, cofactor assays
3. Free Mg++ assays (electrode)
What's the ref range of Mg2+?
0.65-1.05 mMol - just a little lower than phosphate's range.
Name the 4 main hormones of Mineral Metabolism:
1. PTH
2. Calcitonin
3. PTrProtein
4. Vitamin D
2 other names for Vit D:
1. Cholecalciferol
2. Calcitriol
What processes occur in bone remodeling?
1. Bone resorption controlled by osteoclasts/PTH
2. Bone formation controlled by osteoblasts/Calcitonin
How does PTH work?
increases blood Calcium levels by stimulating bone resorption.
Where is PTH produced?
in Parathyroid glands (4 little curds at the base of the thyroid)
How does PTH respond to:
-Decreased serum Ca2+
-Decreased free Mg2+
-Increased vit D
-Decreased serum Ca2+: increase
-Decreased free Mg2+: increase
-Increased vit D: decrease
How does PTH affect phosphate concentration in the body?
It reduces Phosphate reclamation in the renal proximal tubules
What is overall PTH effect on:
-Serum Ca2+ concentration?
-Phosphate concentration?
Ca2+: Increases
Phosphate: Decreases
Where is Vit D derived from?
What regulates Vit D levels?
-Parathyroid hormone
-Phosphate levels
What is the function of Vit D?
To regulate and maintain body Calcium and Phosphate levels
Most important source of Vit D is:
Where is Calcitonin produced?
Parafollicular cells in the thyroid gland
Calcitonin's action is:
decreased osteoclastic function to decrease body calcium levels and build bone.
What influences body Calcitonin levels most?
Body ionized calcium levels
What is PTHrP?
Parathyroid hormone related protein
Where is PTHrP produced?
Lactating breast tissue, cancer, pregnancy, tumors.
What are causes of Hypocalcemia?
-Low Albumin levels
-Chronic renal failure
-Decreased Vit D
What kinds of physical symptoms result from hypo-calcemia?
Muscle spasms and increased neuromuscular excitability
What kind of affect on hormone levels would hypo-calcemia have?
It would increase PTH
It would decrease Calcitonin
What is the primary treatment for hypocalcemia?
Vit D and calcium supplements
What are 3 causes of Hyper-calcemia?
1. Hyperparathyroidism
2. Malignancy
3. Diuretics
What types of physical symptoms result from hyper-calcemia?
What are 3 key symptoms of hyperparathyroidism and hypercalcemia of malignancy?
1. Nausea
2. Vomiting
3. depression/lethargy
What 3 pieces result from PTH metabolism?
1. N-terminal peptide
2. C-terminal peptide
3. Mid-molecule
-Why msr C-terminal PTH?
-Why msr N-terminal PTH?
C: to monitor ongoing changes in disease

N: to monitor therapy response
What's detected in a C-term assay for PTH?
-Mid-molecule PTH
-C-terminal PTH
Therfore, secreted PTH and the C-terminal fragment.
What's detected in an N-term assay for PTH?
-N-term fragments
-Newly secreted PTH
What's detected in an Intact PTH assay?
only intact PTH
How does Intact PTH assay only detect intact?
-By using 2 antibodies.
-No C fragment b/c that would only bind 1 antibody.
-No N fragment for same reason
-PTHrP binds neither Ab.
Most common cause of primary hyperparathyroidism is?
Benign parathyroid tumors; rarely caused by cancer.
Most common cause of 2ndary hyperparathyroidism is?
Chronic Renal Failure
Why does CRF cause hyperparathyroidism?
Kidneys can't excrete phosphate, so serum calcium levels drop to compensate for high serum phosphate; PTH senses the drop, increases to elevate the serum Ca2+.
What other measurement is useful for evaluating PTH?
Nephrogenic cAMP
How is nephrogenic cAMP measured?
-By radioimmunoassay
-Correction for filtration
What exactly does the nephrogenic cAMP assay detect?
All bioavailable PTH (including PTHrP)
What causes hypophosphatemia from intracellular shift?
-Glucose IV
-Respiratory alkalosis
What can cause hyperphosphatemia?
-Renal failure (no excretion)
-Laxatives, enema, hemolysis
-Cell death

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