Makindo Medical Notes | Magnesium Physiology

🔋 Magnesium is an essential mineral and electrolyte critical for hundreds of enzymatic reactions, neuromuscular function, and cellular energy production. It is the fourth most abundant mineral in the human body and the second most abundant intracellular cation.

📊 Distribution of Magnesium

Magnesium stores in the body:
- 🦴 ~60% in bones (structural reservoir).
- 💪 ~20% in muscles.
- 🧬 ~20% in soft tissues and extracellular fluid.
- 💉 Intracellular concentration: 10–20 mEq/L; Extracellular: 0.7–1.0 mmol/L (1.7–2.3 mg/dL).

⚡ Functions of Magnesium

Enzymatic Reactions 🧪 :
- Cofactor for >300 enzymes involved in ATP production, DNA/RNA synthesis, and protein synthesis.
Neuromuscular Function 🧠 :
- Stabilises nerve and muscle membranes by regulating ion channels.
- Prevents over-excitation by counteracting calcium and sodium influx.
Cardiovascular Health ❤️ :
- Maintains normal heart rhythm and vascular tone.
- Supports blood pressure regulation by relaxing smooth muscle.
Bone Health 🦴 :
- Involved in bone mineralisation and calcium/vitamin D metabolism.
Glucose Metabolism 🍬 :
- Enhances insulin action and supports glucose uptake.
- Low magnesium → insulin resistance risk.

⚖️ Regulation of Magnesium Levels

Maintained by diet, kidneys, and GI absorption:
- Dietary Intake 🥦 :
  - Sources: leafy greens, nuts, seeds, whole grains, legumes.
  - Adult requirement: 310–420 mg/day (higher in pregnancy/lactation).
- Renal Excretion 🩺 :
  - Kidneys reabsorb ~95% of filtered magnesium.
  - Most reabsorbed in thick ascending limb of Henle + distal tubule.
- GI Absorption 🧃 :
  - Absorption rate ~30–50% in the small intestine.
  - Enhanced by vitamin D and PTH.

🏥 Clinical Relevance

Hypomagnesemia ⬇️ :
- Causes: Poor intake, diarrhoea, malabsorption, renal loss (diuretics, hyperaldosteronism), PPIs.
- Symptoms: Tremors, muscle cramps, seizures, arrhythmias, ↑ neuromuscular excitability.
- Treatment: Oral/IV magnesium replacement + treat cause.
Hypermagnesemia ⬆️ :
- Causes: Renal failure, excess supplements (antacids, laxatives), adrenal insufficiency.
- Symptoms: Nausea, hypotension, bradycardia, respiratory depression, cardiac arrest (severe).
- Treatment: Stop Mg intake, IV fluids, loop diuretics, dialysis if severe.
Cardiovascular Health ❤️ :
- Low Mg linked to hypertension, arrhythmias, CAD.
- Supplementation may improve heart outcomes in deficiency.
Bone Health 🦴 :
- Chronic deficiency contributes to osteoporosis & fracture risk.
Diabetes & Metabolic Syndrome 🍩 :
- Low Mg → insulin resistance & higher risk of T2DM.
- Correction improves glycaemic control in deficient patients.

📝 Summary

Magnesium is a vital mineral powering energy, nerve, heart, bone, and glucose physiology. Its regulation depends on diet, kidneys, and intestines. Both low and high magnesium states can be dangerous, affecting muscle, heart, and neurological function, making magnesium monitoring crucial in clinical medicine.

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Magnesium Physiology

📊 Distribution of Magnesium

⚡ Functions of Magnesium

⚖️ Regulation of Magnesium Levels

🏥 Clinical Relevance

📝 Summary

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