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22 Cards in this Set
- Front
- Back
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Is Mg micro or macro?
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Micro
AI ~ 300-400mg range nuts, legumes, whole grains |
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Where is Mg found internally?
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99% is found w/in bones or intracellularly - it's the 2nd most abundant intracellular element behind K+
(60% bone/ 25% muscle) 1% in plasma 80% in free form |
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Absorption of Mg
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Absorption occurs in the ileum and colon! Active absorption, ~30-40% absorbed.
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How is Mg homeostatis maintained? (general)
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Through urinary excretion: the amount of Mg reabsorped in the kidney determines amount excreted
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What is the mechanism of Mg homeostatis?
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80% plasma Mg filtered by kidney:
10-20% reabsorbed by proximal convoluted tubule 70-80% reabsorbed by "ascending limb of loop of Henle" 10% absorbed by distal convoluted tubule ** reabsorption is constant except in the ascending limb of loop of Henle. Regulation occurs here. |
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What are the metabolic roles of Mg?
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Mg is involved in most aspects of metaboloism; 300+ enzymes.
Involved in enzyme systems in two ways: • Mg/nucleotide complex: chelation of ATP lowers Ea for rate-limiting step of transphosphorylation • allosteric activation of enzymes (direct binding) |
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Describe the complex between Mg and nucleotide substate
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For example, ATP+Mg:
Mg interacts with the O's on the phosphate groups and with the N of the adenine: reduces negative charge cloud around ATP, lowering Ea of rxns |
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Name some enzymes that Mg binds with directly (allosteric activation)?
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Adenylate cyclase!
Pyruvate kinase, phosphofructokinase |
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What are the signs of Mg deficiency?
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The three hypo's: hypomagnesia, hypocalemia, hypokalemia. AND low circulating levels of PTH.
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Describe the first stage of Mg deficiency? i.e. low mg causes what to happen?
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Failure of heteroionic exchange of Ca/Mg in bone: plasma Ca concentrations down; PTH increases.
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Describe the 2nd stage of Mg deficiency? i.e. low mg causes what to happen?
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End organ PTH resistance develops:
Respons of end organs to PTH mediated by cAMP. Conversion of ATP-> cAMP is catalyzed by adenylate cyclase which is a Mg2+ dependent enzyme. Low intercellular Mg reduces amt of cAMP avaiable. Osteoclasts less reponsive too. |
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Describe the 3rd stage of Mg deficiency? i.e. low mg causes what to happen?
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PTH secretion drops; PTH levels in circulation drops. PTH secreption is cAMP dependent.
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Describe the 4th stage of Mg deficiency? i.e. low mg causes what to happen?
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Lack of PTH/cAMP prevents activation of Vitamin D; lack of Vitamin D prevents Ca absoroption. Lack of D and PTH prevents osteoclast precursur cells from stimulation into Osteoclasts.
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Describe the 5th stage of Mg deficiency? i.e. low mg causes what to happen?
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Lowered K+ reabsorption. Na,K-ATPase activity greatly reduced from lack of Mg.
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What are the two ultimate causes of all of these problems?
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- Lack of adenylate cyclase activity
- Lack at Mg-ATP complex |
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How quickly are the 3 hypos rectified after Mg supplementation?
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Mg/PTH increases within MINUTES. PTH was there, just couldn't be secreted.
Ca takes longer since Active Vit D needs to be synthesized. |
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How is Mg involved in genes?
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1. Involved in DNA replication
2. Involved in DNA repair |
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What types of DNA repair in Mg needed for/ describe Mg's role.
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Two types of DNA repair:
1. NER - nucleotide excision repair (chucks out/replaced) 2. BER - base excision repair (single base removed/repaired) Mg needed in a number of these steps. |
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Name the enzyme which is Mg-dependent in BER.
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APE1: this protein is responsible for coordination of removal and transfer of damaged base to repair enzyme.
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Besides the three hypos, what are some other deficiency signs of Mg?
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Almost zero urinary excretion
• Neuromuscular signs: trousseau's compression of upper arm (arm spasms), muscle weakness, temors, headaches • Naseua/ personality changes • Anemia |
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What is the biochemical method of assesment for Mg?
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Mg plasma concentration. If it's low, you are deficient, but if it's normal, you may/may not be deficienct.
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When does Mg deficiency occur?
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Anything that mucks up kidney
: decrease in renal absorption. Seen almost exclusively in hospital patients (because of other conditions) |
