Magnesium Disorders Physiology Flashcards
What is the total body magnesium content in a 70kg adult?
~25g
Distribution: Bone (67%), Muscle (20%), Other tissues (12%), Extracellular (1-2%)
What percentage of magnesium is found in free ionized form in plasma?
60%
This form is biologically active.
What are the main sites of intestinal absorption for magnesium?
Jejunum & ileum
Mechanisms include paracellular (80-90%) and transcellular (10-20%) absorption.
What mechanisms are involved in magnesium intestinal absorption?
- Paracellular (80-90%)
- Transcellular (10-20%)
Paracellular absorption is passive via claudins, while transcellular absorption involves TRPM6/7 channels.
What regulator increases magnesium absorption?
1,25(OH)₂D₃
This is a form of vitamin D.
What dietary condition decreases magnesium absorption?
High Ca²⁺/PO₄ diet
High levels of calcium and phosphate can inhibit magnesium absorption.
What is the filtered load of magnesium in the kidneys?
~2000 mg/day
This is the amount of magnesium filtered by the kidneys daily.
What is the typical percentage of magnesium reabsorbed in the proximal tubule (PT)?
20%
This reabsorption is passive and follows Na⁺/H₂O.
What percentage of magnesium is reabsorbed in the thick ascending limb (TAL)?
60-70%
Reabsorption in TAL is paracellular and driven by lumen+ voltage.
What is the active magnesium reabsorption percentage in the distal convoluted tubule (DCT)?
5-10%
This process occurs via TRPM6 channels.
How much magnesium is normally excreted of the filtered load?
5%
Excretion can be adjusted based on the body’s needs.
What are the primary magnesium channels in the intestine and DCT?
TRPM6/7
These channels play a crucial role in magnesium transport.
Which tight junction proteins are important for magnesium handling in TAL?
Claudins 16/19
These proteins facilitate paracellular transport of magnesium.
What is the function of FXYD2 in magnesium regulation?
γ-subunit of Na⁺/K⁺-ATPase
It is involved in magnesium transport at the DCT basolateral exit.
What happens to magnesium reabsorption in hypomagnesemia?
↑ Reabsorption (↓ excretion to 0.5%)
The body compensates by retaining more magnesium.
What is the effect of hypermagnesemia on magnesium reabsorption?
↓ Reabsorption (↑ excretion to 50%)
The body excretes more magnesium when levels are high.
Which hormone increases magnesium reabsorption?
PTH
Parathyroid hormone plays a role in magnesium homeostasis.
What role does EGF play in magnesium regulation?
↑ TRPM6 activity
Epidermal growth factor enhances the function of magnesium channels.
What is one of the functions of magnesium in the body?
- Enzyme cofactor
- Membrane stabilization
- Nucleic acid synthesis
- Ca²⁺ channel antagonist
- K⁺ homeostasis
Magnesium plays multiple critical roles in cellular functions.
What does the mnemonic ‘MAGNESIUM’ stand for?
- M: Membrane stabilization
- A: ATP utilization
- G: Gene expression
- N: Neuromuscular function
- E: Enzyme cofactor
- S: Second messenger
- I: Ion channel regulator
- U: Uptake via TRPM6/7
- M: Metabolic reactions
This mnemonic helps remember the functions of magnesium.
True or False: Serum magnesium levels accurately reflect total magnesium stores in the body.
False
Serum magnesium levels do not provide a complete picture of total body magnesium.
What is the major regulatory site for magnesium in the kidneys?
DCT
The distal convoluted tubule is crucial for magnesium regulation.
What genetic condition can result from TRPM6 mutations?
Hereditary hypomagnesemia
This condition is characterized by low magnesium levels due to impaired absorption.
What is a risk for patients with chronic kidney disease (CKD) regarding magnesium?
Both hypo/hypermagnesemia
CKD can lead to imbalances in magnesium levels.
