11 - Ca, PO4, Mg

Question 1

electrolyte rule of 3s

Answer 1

Ca, P, Mg
controlled by PTH, VitD, phosphatonins
affect bone, intestine, kidney

Question 2

PTH - stimulated by, inhibited by

Answer 2

stim: low ionized Ca (inactivation of Ca Sensing Receptor)
inc serum phosphate, low serum Mg

inhib: inc ionized Ca levels
calcitriol

Question 3

how are hypomagnesemia and hypocalcemia associated with each other?

Answer 3

hypomagnesemia affects cGMP signaling > PTH unable to work at bone / release Ca

Question 4

how does PTH inc serum Ca?

Answer 4

inc resorption of bone > release Ca and PO4
inhibit PO4 reabs in kidney in PCT (less PO4 to bind Ca > more free Ca)
inc reabs of Ca in DCT and stimulates renal 25(OH)D-1-hydroxylase > activation of vit D > abs of Ca from GI tract

Question 5

Ca sensing receptor - location

Answer 5

kidney, parathyroid gland, intestine

Question 6

action of Ca sensing receptor (CaSR) in parathyroid gland

Answer 6

less PTH produced

Question 7

action of CaSR in kidney

Answer 7

thick ascending loop
when activated, inhibits apical K channel
Ca absorption stops
end result is like furosemide > calciuresis

Question 8

treating hyperPTH

Answer 8

cinacalcet - binds to CaSR

also can try calcitriol (form of vit D) for feedback inhibition, or surgical parathyroidectomy

Question 9

activation of Vit D

Answer 9

first by 25-hydroxylase in liver

then 1-alpha hydroxylase in kidney

Question 10

another name for activated vit d

Answer 10

calcitriol

Question 11

what stimulates activation of vit d?

Answer 11

PTH (feedback)
low PO4, low Ca
estrogen, prolactin, calcitonin, growth hormone

Question 12

actions of calcitriol

Answer 12

inc Ca, Mg, PO4 abs in intestine

inhibit PTH secretion

Question 13

phosphatonins - example, where made, what is main message

Answer 13

FGF23
bone
tells kidneys to dump PO4

Question 14

what hormone is high in CKD due to PO4 retention?

Answer 14

phosphatonins

Question 15

calcitonin

Answer 15

minor role in Ca reg
opposite of PTH
lowers serum Ca

Question 16

nl serum Ca

Answer 16

9-10.4 mg/dl

Question 17

serum Ca distribution and how it is affected by change in acid base state

Answer 17

nl - 45% protein bound, 45% ionized, 10% complexed
acidosis - inc ionized Ca
alkalosis - dec ionized Ca

Question 18

where in the nephron is Ca transport hormone regulated?

Answer 18

DCT

Question 19

how to correct serum Ca for albumin

Answer 19

corrected = Ca + (4-albumin)*0.8

Question 20

etiologies of hypocalcemia

Answer 20

absence of PTH gland/function
hypomagnesemia
ineffective PTH - vit D def, malabsorption of Ca
PTH overwhelmed - hyperphosphatemia causes Ca PO4 complexing

Question 21

presentation of hypocalcemia

Answer 21

tetany, Trousseau and Chvostek signs
seizures, neuropsych changes
prolonged QT, arrhythmias, hypotension, HF
coarse scaly skin, cataracts

Question 22

tx of hypocalcemia

Answer 22

correct underlying dz

give Ca and/or vit D

Question 23

causes of hypercalcemia

Answer 23

hyperPTH
acidemia
immobilization (>breakdown of bone)
vit D and Ca abs in GI, lots of milk
thiazide diuretics
familial hypercalcemia
granulomatous production and calictriol

Question 24

presentation of hypercalcemia

Answer 24

“bones stones groans abd moans”
vasoconstriction, HTN, short QT
ulcers, constipation, pancreatitis
lethargy, obtundation, psychosis, weakness
extraskeletal calcifications - dermal, ocular, vascular, visceral organs

Question 25

how can hypercalcemia affect kidney?

Answer 25

AKI nephrogenic DI stones calicifications

Question 26

tx for hypercalcemia

Answer 26

optimize renal excretion by giving Na and water to lessen reabs in PCT, promote Ca loss at LoH w/ loop diuretics inhibit bone resorption w/ calcitonin or bisphosphonates ** most important is aggressive volume replacement

Question 27

MCC hypercalcemia (2)

Answer 27

primary hyperPTH and malignancy

Question 28

how is GI abs of PO4 regulated?

Answer 28

inc by calcitriol | no way to reduce it though - kidneys must remove excess absorbed

Question 29

how is PO4 reabs in the kidney handled?

Answer 29

most reabs in PCT | inhib by PTH and FGF23 via reducing transporter expression

Question 30

causes of hypoPO4

Answer 30

``` severe alcoholism gluc infusion after starvation elevated PTH Fanconi syndrome PO4 binding antacids vit D deficiency > dec GI abs certain tumors / neoplastic syndrome ```

Question 31

presentation of hypoPO4

Answer 31

``` acute: inadequate ATP production muscle weakness/necrosis cardiac failure, neurologic dysfunction hemolysis, tissue hypoxia impaired platelet and macrophage function ``` chronic - inc bone resorption - demineralization and pain

Question 32

tx of hypophosphatemia

Answer 32

milk, cheese, eggs, supplements | IV in emergencies, but can cause severe hypocalcemia by complexing w/ Ca

Question 33

causes of hyperPO4

Answer 33

tumor lysis rhabdomyolysis (also trauma/crush) kidney dz

Question 34

consequences of hyperPO4

Answer 34

complexes w/ Ca > deposits everywhere. Calciphylaxis has VERY high mortality secondary hyperPTH: hypocalcemia due to complexing > release of PTH osteitis fibrosa cystica and metastatic califications

Question 35

tx of hyperPO4

Answer 35

correct underlying problem | 3 d's: diet, dietary binders (PO4 binders like Mg, Al, Ca, etc), dialysis

Question 36

causes of Mg cell efflux and influx

Answer 36

efflux - beta stim | influx - insulin, calcitriol, vit B6

Question 37

role of Mg in body

Answer 37

DNA/protein synth neuronal activity, cardiac excitability, vasomotor tone / BP cofactor for transport of K and Ca

Question 38

where is most Mg reabs in kidney?

Answer 38

thick ascending limb

Question 39

hypomagnesemia cause

Answer 39

malnutrition, alcoholism, malabsorption | renal wasting after nephrotoxic drugs

Question 40

hypomagnesemia presentation

Answer 40

muscle weakness, tremors, fasciculations, arrhythmias neuro/psych changes hypocalcemia, hypokalemia

Question 41

hypermagnesemia causes

Answer 41

iatrogenic (use as tocolytic) | Mg containing antacids

Question 42

presentation of hypermagnesemia

Answer 42

thirst, nausea, vomiting drowsiness, hypotension, depressed DTR coma, resp paralysis, cardiac arrest

Question 43

tx of hypermagnesemia

Answer 43

initial - IV Ca - stabilize heart loop diuretics dialysis