FINAL: magnesium Flashcards
Mg is a __ metal that makes __ ions in solution
Mg is a divalent metal that makes positive ions in solution
after K+, Mg2+ is the most abundant __ ion
after K+, Mg2+ is the most abundant intracellular ion
Mg is more __ and less __ than Ca
Mg is more hydrated and less flexible than Ca
since Mg is very hydrated,
Mg must be dehydrated to be used
Mg mainly binds to __
Mg mainly binds to phosphate (like in ATP)
3 properties of Mg
- binds organic anions (ATP, nucleotides)
- binds enzymes to alter catalytic activity
- competes with calcium for binding sites
2 functions of ATP
energy
make DNA, RNA
Mg blocks __ to regulate it
Mg blocks calcium to regulate it
dietary source of Mg
ALL plant and animal foods
green leafy veg (chlorophyll)
fish
nuts
what type of grain is best for Mg?
whole grains bc polished grains have depleted Mg
is Mg a nutrient of concern?
YES
__% of Americans don’t get enough Mg
48% of Americans don’t get enough Mg
when does Mg RDA increase
pregnancy, not lactation
is Mg non-toxic?
yes
does Mg have an upper limit?
yes
signs of Mg toxicity
diarrhea
nausea
flushing
double vision
muscle weakness (Ca2+ related)
excessive Mg intake causes
diarrhea and dehydration (Mg is found in some laxatives)
intestinal fractional absorption of Mg is __ related to intake
intestinal fractional absorption of Mg is inversely related to intake
higher intake of Mg = __ absorption
higher intake of Mg = decreased absorption
__% Mg absorbed
30-50% Mg absorbed
Mg absorption is good in __ but decreases with __
Mg absorption is good in children but decreases with age
where in intestine is Mg absorbed?
distal jejunum and ileum
intestinal absorption of Mg steps
- digestion separates Mg from proteins
- TRPM6 (apical) lets Mg into cell (no chaperone needed)
- Mg exits into blood, Na enters cell (antiporter)
- ATPase sends Na out
main type of Mg in blood
free Mg
inhibitors of intestinal absorption of Mg
- alcohol
- phytic acid (traps Mg)
- fiber
- fatty acids
where does Mg go when inhibitors are present?
feces
with high Mg intake,
transporter is saturated, passive paracellular transport to portal blood
passive paracellular transport of Mg is upregulated by
calcitriol and PTH
when is active Mg saturable
at physiological range
where is Mg found in body
54% in skeleton
45% in soft tissues
1% in EC fluid
is Mg IC or EC
IC!
in what people is serum Mg rly high
vegetarians and vegans
__ stimulates release of Mg from bone
PTH stimulates release of Mg from bone
where is Mg lost
plenty in feces, some in urine
what type of treatments affect Mg
diuretics: treatments that target urinary filtration
what is the central organ of Mg homeostasis
kidney
5-15% Mg reabsorbed in __
65-75% __
5-10% __
5-15% Mg reabsorbed in proximal tubule
65-75% thick ascending limb
5-10% convoluted tubule
up to __% of filtrated Mg is reabsorbed
up to 95% of filtrated Mg is reabsorbed
to preserve Mg, __ can be reduced to 1%
to preserve Mg, urinary excretions can be reduced to 1%
increased Mg excretion and decreased resorption caused by
diuretics
alcohol
resorption of Mg is passive in __
active in __
resorption of Mg is passive in thick ascending loop
active in distal convoluted tubule
during passive resorption in thick ascending loop,
__ and __ inhibits
__+__ increases resorption
during passive resorption in thick ascending loop,
Mg and Ca inhibits
PTH + vit D increases resorption
why is resorption passive in thick ascending loop but not in distal convoluted tubule
there is a voltage gradient in thick ascending loop
active resorption in distal convoluted tubule steps
- TRPM6/7 brings Mg in
- antiporter brings Na in, Mg out
- Na out by NaK ATPase (basolateral)
what transporter brings Mg back into circulation?
TRPM6/7
How is Mg extruded into blood?
secondary active antiporter
How do we get Na out of cell?
primary active ATPase
Mg regulates cell activities by associating with organic polyphosphates (3)
ATP
IP3
RNA, DNA
Mg binds and stabilizes these proteins
enolase, pyruvate kinase
myosin (muscle contraction)
Mg binds and stabilizes these proteins
enolase, pyruvate kinase
myosin (muscle contraction)
overview functions of Mg
- energy metabolism (binds ATP to stabilize)
- nucleic acid and protein synthesis
- secondary messenger (IP3 allows Ca2+ exit)
- regulate ion channels (mainly Ca2+)
role of IP3
allows Ca2+ exit
Mg ion trafficking
1) Mg regulates
2) Mg blocks
Mg ion trafficking
1) Mg regulates NaK ATPase
2) Mg blocks Ca channels at right times
why is Mg deficiency so bad?
it causes K+ deficiency which has CV effects and can be deadly
Mg deficiency
reduced __ in skeletal muscle = K+ depletion
Mg deficiency
reduced NaK pump in skeletal muscle = K+ depletion
Mg deficiency
down-regulation of __ channels in heart
Mg deficiency
down-regulation of Mg-sensitive K+ channels in heart
Mg deficiency
increased uptake and release of __ = increased __ = problems with muscle contraction
Mg deficiency
increased uptake and release of calcium = increased IC calcium = problems with muscle contraction
Mg deficiency causes __ symptoms
Mg deficiency causes CV symptoms
CV symptoms caused by Mg deficiency
EKG changes
vasospasms
increased BP
arrhythmia
is there a reliable way to assess Mg?
no
3 ways to assess Mg
- plasma (most used, not sens and spec)
- RBC levels (better long term)
- urinary excretion (~80% IV Mg load normall excreted, less is bad)
why is plasma bad to assess Mg
like Ca, phosphate, Mg in plasma can look normal when tissue is low
