Magnesium Flashcards
How much of Mg is stored IC versus EC?
99% IC - second most abundant IC cation (after K)
What are the proportions of ionized, protein-bound, and complexed magnesium in plasma?
ionized 65%
protein-bound 30%
complexed 5%
CCM
Dibart: 55, 20-30, 10-15
Where in the GI tract is magnesium absorbed?
mostly ileum
jejunum and colon just contribute
Where in the tubules is most Mg reabsorbed and by what mechanism?
- ascending thick loop of henle (only cortical part)
- suspected to be mainly by paracellular route
How do hypokalemia, hypophosphatemia, and acidosis affect Mg absorption in the kidneys?
decrease Mg absorption
What are the symptoms of hypermagnesemia?
- loss of deep tendon reflexes/hyporeflexia
- loss of mencase and palpebral reflexes
- impaired respiration from respiratory muscule weakness
- mild to moderate hypotension
- ECG derangements - conduction disorders
- weakness, lethargy, depression
- neuromuscular blockade
What organs store most Mg?
bones 60%
muscles 20%
List substances Mg can complex with
phosphate
citrate
lactate
bicarbonate
sulfate
List functions of Mg (5)
- cofactor for ATPase pumps - NaKATPase, CaATPase + proton pumps
- needed for protein and nucleic acid synthesis
- regulation vascular smooth muscle tone
- cellular second massenger system and signal transduction
- immune system: leukocyte activation, cytokine production, inflammation
List causes for hypomagnesemia
Decreased intake or absorption
* takes weeks if dietary intake
* evidence in people prolonged PPI causes decreaed absorption
GI losses - e.g., diarrhea
Renal losses
* kidney disease
* endocrinopathies causing increased FeMg (DKA and hyperthyroidism)
* diuretics (furosemide, thiazides, mannitol)
Change of iMg proportion
* glucose, bicarbonate, or amino acid administration»_space; shift iMg IC
* catecholamines»_space; beta adrenergic stimulated lipolysis»_space; free fatty acids chelating iMg
* administration of citrated blood products
* pancreatitis»_space; forms insoluble soaps
What are clinical signs of hypomagnesemia?
- arrhythmias
- hypertension
- platelet aggregation
- coronary artery vasospasm
- muscle weakness, fasciculations, ataxia, seizures
- respiratory and GI muscle weakness
- hypokalemia, hyponatremia, hypocalcemia
What ECG changes/arrhythmias
- atrial fibrillation
- SVT
- VT
- Vfib
- prolonged PR interval
- widened QRS complex
- depressed ST segment
- peaking T wave
How does hypomagnesemia cause neuromuscular signs?
- low Mg»_space; increaes acetylcholine releae from nerve terminals»_space; enhanced excitability
- increased IC Ca++ of skeletal muscles
How does hypomagnesemia cause hypocalcemia?
- suppressed PTH releae
- enhances Ca movement into the bones
What are ECG changes seen with hypermagnesemia?
- prolonged PR interval
- widened QRS complex
- mechanism: delayed AV and interventricular conduction
- bradycardia
