electrolytes 3( Mg+,Ca+,HPO,lactate) Flashcards
Magnesium
- 4th most abundant cation in the body (after Na+, K+, Ca2+)
- 2nd most abundant intracellular cation (after K+)
- Mg2+ in the body can be found in:
- Bone (53%) mostly**
- Muscle, organs, soft tissue (46%)
- Serum and RBCs (<1%)
- Magnesium Distribution
- of Mg2+ is bound to protein ( mostly albumin )
- 61% exists in the free or ionized state**
- 5% complexed with other ions (phosphate, citrate)
• Only the free ion is physiologically active** IN A FORM THAT CAN BE USED BY THE BODY
role of magnesium
- Cofactor for more than 300 enzymes
- Transcellular ion transport
- Neuromuscular transmission
- Synthesis of carbohydrates, proteins, lipids and nucleic acids
- Release of and response to certain hormones
dietary magnesium
• Raw nuts • Dry cereal • Vegetables • Meats • Fish • Fruit • The small intestine can absorb 20-65% of dietary Mg2+. Regulation
regulation of magnesium
• Regulation of Mg2+ is largely controlled by the kidney.
- Reabsorbed when there is a deficit
- Excreted when in excess
• Reabsorption of Mg2+:
- 25-30% of non-protein bound Mg2+ is reabsorbed by the proximal convoluted tubule (less than Na+: 60-75%).
- 50-60% is reabsorbed in the ascending Loop of Henle*****
- 2-5% reabsorbed in the distal convoluted tubule.
hormone regulation of magnesium
• Parathyroid hormone (PTH)
- Increases renal reabsorption of Mg2+
- Enhances absorption of Mg2+ in the intestine
- Aldosterone and Thyroxine
- Increases renal excretion of Mg2+
specimen for magnesium
- Serum
- Lithium heparin plasma
• Avoid hemolysis and separate cells from serum ASAP
- [Mg2+] inside RBCs are 10X higher than in the ECF
• Unacceptable anticoagulants:
- Oxalate, citrate, EDTA
- They will bind with Mg2+
• Urine -24-hour specimen preferred
- Must be acidified with HCl to prevent precipitation
magnesium - methods of deteminants
The most common methods involve colorimetry:
** just know that there are 3 main types for colorimetry
- Calmagite
• Mg2+ combines with calmagite to form a reddish-violet complex
• Read @ 532 nm - Formazan Dye
• Mg2+ binds with the dye to form a colored complex
• Read @ 660 nm - Methylthymol Blue
• Mg2+ binds with the chromogen to form a colored complex
• Reference method: Atomic Absorption Spectrophotometry (AAS)**
when is magnesium most frequently observed
in hospitalized patients in ICUs; rarely seen in non hospitalized patients
Clinical significance of magnesium
Hypomagnesemia
causes: reduced intake, decreased absorption, increased excretion
symptoms: tetany *** irregular muscle spasms
Hypermagnesemia
causes: renal failure is most common cause **, increased intake ( renal failure plus taking meds that increase Mg2+)
symptoms: GI. decreased thrombin, neurological
Reference range of magnesium
0.63-1.0 mmol/L
distribution of calcium in the blood
~ 99% of calcium in the body is part of bone <1% is in the extracellular fluid (ECF)
• Calcium exists in plasma in three states:
1) 40% is protein bound
- 80% of which is bound to albumin
- 20% of which is bound to globulins
2) 15% is bound to anions (HCO3-, citrate, lactate)
3) 45% is ionized (Ca2+)
- Physiologically active form
- Protein-bound calcium is non-diffusible and cannot pass through capillary
walls.
- Anion-bound and ionized forms ARE diffusible and can pass through capillary walls.
Functions of Calcium
1) Structural component of bones and teeth
2) Necessary for blood coagulation
3) Required for transmission of nerve pulses } K+ also needed
4) Required for muscle contraction and normal heartbeat } K+ also needed
5) Necessary for activation of some enzymes
6) Role in the transfer of inorganic ions across cell membranes
- i.e. membrane permeability
Calcium balance in blood ( 3 processes)
- Maintained by 3 processes:• Absorption (intestine)
- Excretion (kidney)
- Movement in/out bone
calcium balance in blood 3 hormones
- These processes are regulated by 3 hormones:• Parathyroid Hormone (PTH)
- Calcitonin (CT)
- Vitamin D • 1,25-dihydroxycholecalciferol (1,25-(OH)2D) is the active form of vitamin D
- Converted to the active form by hydroxylation in the kidneys
calcium absorption in the intestines is increased & decreased by
Increased by:
• Increased protein intake (40% Ca bound)
• Low gut pH increases solubility• Vitamin D (needed for Ca absorption)
• PTH (makes active Vitamin D)
Decreased by: • Low protein • High pH decreases solubility • Excess Fatty Acids (complex with Ca) • Phytic acid (insoluble complex) • Increased serum phosphate • Calcitonin
• Serum calcium is regulated by: PTH, vitamin D, and calcitonin
calcium and parathyroid hormone
- PTH secretion is stimulated by a ↓ in ionized Ca2+
- Secretion is stopped by an ↑ in ionized Ca2+
• Exerts three effects on bone and kidney:
In the bone:
1. Activates bone resorption
• Activated osteoclasts break down bone and release Ca2+ into ECF
In the kidney:
- Increases tubular reabsorption of Ca2+
- Stimulates renal production of active vitamin D
