Chap 53 Mg++ and Phos Flashcards
Objective
To review magnesium physiology including absorption, excretion, and function within the body, causes of magnesium abnormalities, and the current applications of magnesium monitoring and therapy in people and animals.
Etiology
Magnesium plays a pivotal role in -
Disorders of magnesium can be correlated with severity Septic patients and Mg -
Hypermagnesemia is seen -
Hypomagnesemia is more common in critically ill people and animals, and can be associated with -.
Diagnosis
Measurement of serum ionized magnesium
Tissue magnesium concentrations may be assessed -
Therapy
Magnesium infusions may play a therapeutic role in -
Further veterinary studies are needed to establish the frequency and importance of magnesium disorders and benefit of magnesium infusions as a therapeutic adjunct to specific diseases
Objective
Etiology
energy production and specific functions in every cell
disease, length of hospital stay, and recovery of the septic patient.
uncommon
platelet, immune system, neurological, and cardiovascular dysfunction
alterations in insulin responsiveness and electrolyte imbalance
using nuclear magnetic resonance spectroscopy as well as through the application of fluorescent dye techniques.
Therapy
(being used in human med) reperfusion injury, myocardial ischemia, cerebral infarcts, SIRS, tetanus, digitalis toxicity, bronchospasms, hypercoagulable states, and as an adjunct to specific anesthetic or analgesic protocols
HypoMg does what to mitochondria:
vet school - lactation tetany =
uncoupling of oxidative phosphorylation in rat heart mitochondria
Magnesium Distribution
intracellular:
extracellular:
1% serum Mg is divided into:
___%protein bound
___%complexed
___% ionized
0.5% ionied and active form
Of the protein‐bound serum magnesium, ___% is bound to albumin with the remainder bound to globulins
all cells contain magnesium, but largest the largest tissue fraction is in ___ (67%)
bone magnesium lies within the mineral lattice
Skeletal muscle contains 20%
other soft tissues contain 19%
Magnesium Distribution
99%
1%
30–40%
4–6% to anions: citrate, phosphate, bicarbonate, lactate, or sulfate
55–65%
60–70%
bone (67%)
mineral lattice with a lesser amount part of the surface‐limited exchangeable pool
surface‐limited exchangeable bone can be mobilized
Cytosolic magnesium is maintained at a constant concentration of ____ despite significant fluctuations in extracellular magnesium
Influx and efflux of magnesium across the cell membrane is driven by the concentration gradient of magnesium and calcium passing through
0.5–1 mmol/L
the transient receptor potential melastatin (TRPM) channels (linked to Gs cAMP recep - B agonist stim)
Which 2 pumps require magnesium as a cofactor:
How does Mg affect ATP transport into mitochondria
and what does low Mg do to mitochondria:
activation of T cells
depolarization of myocardial cells and neurons contractility of the vascular endothelium
Na/K-ATPase and calcium-ATPase
without the magnesium ion, ATP cannot be transported into the mitochondria or effectively hydrolyzed to release energy.
uncoupling of oxidative phosphorylation in rat heart mitochondria
As a divalent cation, magnesium competes with calcium for many of the divalent cation channels and receptor sites. Magnesium will compete with calcium for passage through:
Magnesium is a cofactor required for:
transient receptor potential cation (TRPM)
DNA and RNA polymerase, making it essential for protein synthesis
Magnesium homeostasis is primarily a function of:
hypomagnesemia is almost always caused by disturbances in one or both of these organ systems
Most cases of hypermagnesemia involve:
Severe hypomagnesemia and hypermagnesemia cause clinical signs associated with:
intestinal absorption and urinary excretion
renal insufficiency
cardiovascular and neuromuscular systems
Simplified roles of Mg:
ATP:
Pumps 3:
proteins and DNA:
regulation of vascular smooth muscle tone, cellular second messenger systems, and signal transduction
production of ATP - transpot in and mitoch func
coenzyme Na/K-ATPase pump maintain the sodium-potassium gradient across all membranes
Ca-ATPase
proton pumps
protein and nucleic acid synthesis
loop of Henle is the main site of:
kidney main regulator of serum magnesium
achieved by both GFR & tubular reabsorption:
Renal magnesium excretion will increase in proportion to the load presented to the kidney; conversely, the kidney conserves magnesium in response to a deficiency
magnesium reabsorption
no hormone reulation
Magnesium is freely filtered through the glomerulus, with >95% of the filtered magnesium reabsorbed by the tubules. The thick ascending limb (TAL) of the loop of Henle absorbs the largest fraction (80%), followed by the proximal tubules (5–15%) and the DCTs (5–10%).44, 49 Magnesium absorption in the TAL is accomplished by a passive paracellular process driven by the lumen‐positive electrochemical gradient within this segment.49 Factors such as increased luminal flow, hypercalcemia, and hypocalcemia can decrease magnesium reabsorption in the TAL.
The quantity of magnesium reabsorbed from the DCT has a profound impact on total body and urine magnesium concentrations.44, 50, 51 Reclamation of magnesium in the DCT is an active transcellular process and can be regulated by PTH, 1,25‐dihydroxyvitamin D, prostaglandin E2 (PGE₂), adenosine, antidiuretic hormone, calcitonin, aldosterone, glucagon, and insulin
Magnesium is freely filtered through the glomerulus, with >95% of the filtered magnesium reabsorbed by the tubules. The thick ascending limb (TAL) of the loop of Henle absorbs the largest fraction (80%), followed by the proximal tubules (5–15%) and the DCTs (5–10%).44, 49 Magnesium absorption in the TAL is accomplished by a passive paracellular process driven by the lumen‐positive electrochemical gradient within this segment.49 Factors such as increased luminal flow, hypercalcemia, and hypocalcemia can decrease magnesium reabsorption in the TAL.
The quantity of magnesium reabsorbed from the DCT has a profound impact on total body and urine magnesium concentrations.44, 50, 51 Reclamation of magnesium in the DCT is an active transcellular process and can be regulated by PTH, 1,25‐dihydroxyvitamin D, prostaglandin E2 (PGE₂), adenosine, antidiuretic hormone, calcitonin, aldosterone, glucagon, and insulin
Causes Three general categories are involved: decreased intake (or absorption): increased losses: see below alterations in distribution:
increased losses:
GI:
Renal:
Drugs:
Causes
- inadequate nutritional intake, IVFT
- renal vs GI vs drugs/other
- glucose, insulin, shift i, massive trans (chelation)
Gastrointestinal Malabsorption syndromes Extensive small bowel resection Chronic diarrhea Inflammatory bowel disease Cholestatic liver disease
Renal Intrinsic tubular disorders Glomerulonephritis Acute tubular necrosis Postobstructive diuresis
Drug-induced tubular injury Aminoglycosides Amphotericin B Furosemide Thiazides Mannitol Digitalis administration
Diabetic ketoacidosis
Hyperthyroidism
Primary hyperparathyroidism
Lactation
