Electrolytes

Master answer

Normal Magnesium:

1000mmol (12mmol/kg)

Normal Distribution of magnesium

1. Bone (60%)
2. ICF (40% esp organs/muscles)
   • Mg2+ is mainly an IC cation
   • Total IC [ ] 15 mmol/L cf. 0.5 mmol/L free/ionised inECF
3. ECF (< 1%)
   • Plasma [ ] 0.5-1 mmol/L
     • 60% free/ionised
     • 33% protein-bound (esp albumin)
     • 7% complexed (citrate/PO4)

Normal Intake:

8-20 mmol/day (min 0.5 mmol/day)

Normal Losses

• Glomerular filtration of 100 mmol/day
  • 95% reabsorbed in tubules (PCT 15%, 70% LoH, 10% distal nephron)
  • 5% excreted → 2.5 to 8 mmol/day
• Minimal neurohormonal regulation of Mg2+
  • TMAX of Mg transporter ~ plasma [Mg]
  • → ↓reabsorption with ↑ Mg

Normal Functions:

1. Co-factor in enzyme reactions (as a metallo-coenzyme) eg Na+/K+ ATPase activity
2. Energy storage, utilisation, transfer (via role in formation/utilisation of ATP) eg BSL homeostasis
3. Protein and nucleic acid synthesis (stabilises DNA and RNA structure)
4. Ca2+/K+ metabolism
5. ↓ membrane excitability (eg. muscles/nerves)
6. ↓ NT release at cholinergic and adrenergic synapses
7. Antagonises Ca2+ activity

Gladwin 2016

Answer by Gladwin