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Mineral Metabolism
CLASSIFICATION OF MINERALS
Two Types|
PRINCIPAL ELEMENTS |
TRACE ELEMENTS |
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CALCIUM (Ca)
- Total Calcium in human body: 1 – 1.5 Kg
- In Bones – 99 %
- In extra cellular fluid – 1 %
- Sources : -
- Milk (Cow’s Milk – 100mg/100ml)
- Egg, Fish, Vegetables - moderate
- Cereals (wheat, rice) - poor source
- Daily Requirement
- Adults : 500 mg/day
- Children : 1200 mg/day
- Pregnancy and Lactation : 1500 mg/day
- >50 yrs. : 1500 mg/day +20µg Vit.D (to prevent osteoporosis)
- Absorption
- 1st and 2nd part of duodenum
- Against concentration gradient and requires energy
- Requires carrier protein
Factors promoting Ca absorption |
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Factors Inhibiting Ca absorption |
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Functions
- Formation of bone & teeth.
- Osteoblasts → bone deposition
- Osteoclasts → demineralization.
- Muscle Contraction
- Nerve Conduction
- Secretion of hormones : Mediates the secretion of Insulin, PTH, Calcitonin, Vasopressin etc.
- Second Messenger : Ca & cyclic AMP are 2nd messengers of different hormones. Eg: Glucogan
- Membrane integrity & Permeability
- Blood Coagulation : Factor IV in blood coagulation cascade. prothrombin → Thrombin
- Action on Heart : Ca prolongs Systole. ↑ Ca concentration → ↑ myocardial contractility
- Activation of Enzymes : Calmodulin
Plasma Calcium
- Normal Plasma / Serum Calcium : 9 – 11 mg / dl
- Ionized Calcium : 5 mg/dl
- Protein bound Calcium : 4 – 5 mg/dl
- Complexed with phosphate/citrate/ bicarbonate : about 1 mg/dl
Homeostasis of Ca
The major factors that regulate the plasma Calcium are
SODIUM
- Chief cation of extra cellular fluid
- About 50% of body sodium presence in Bone, 40% in extra cellular fluid & 10% in soft tissue.
- DIETARY REQUIRMENT
- Normal individual- 5-10 gm/day as NaCl(10gm NaCl= 4gm Na)
- Hypertensive- Not more than 1gm/day
- BIOCHEMICAL FUNCTION
1. Regulate Acid-Base balance in association with Cl- and Bicarbonate.
2. Maintain Osmotic pressure & fluid balance.
3. Necessary for normal muscle irritability and cell permeability.
4. Promotes intestinal absorption of Glucose, Galactose & Amino Acid.
- PLASMA SODIUM LEVEL
- Normal serum level (Present as extra cellular cations) = 135-145meq/L
- Blood cellular level= 35meq/L
- ABSORPTION
- Absorbed mainly on GI Tract
- Less than 2% normally found in feces
- EXCREATION
- Kidney is the major source of excretion
- 800mg/day filtered through glomeruli
- 99% of this reabsorbed by renal tubules by active process controlled by ALDOSTERONE.
- Through skin in case of extreme sweating. However there is individual variation in sodium loss through sweat.
IRON
- Total contain about 3-5 gm in an adult individual.
- 70% presence in erythrocytes of blood as a constitute of hemoglobin ,5% in myoglobin in muscles.
- Heme is the most predominant iron containing substance.
- Constituents of several proteins & enzymes like
- Hemoglobin
- Myoglobin
- Cytochrome
- Xanthine Oxidase
- Certain other proteins contain ‘non- heme’ iron like Transferrin Ferritin Hemosiderin
ABSORPTION, TRANSPORT & STORAGE
- In normal individual 10% of dietary iron is usually absorbed.
- Dietary iron mainly absorbed in stomach and duodenum.
- Iron mainly found in foods in ferric form (Fe+++) which bound to protein and organic acids.
- Iron in ferrous form is soluble and readily absorbed.
STORAGE OF IRON
As FerritinLiver Spleen Bone MarrowAs Hemosiderin
- Hold 25% of Fe by weight
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- Hold 35% Fe by weight.
- Hemosiderin accumulates in the body particularly in Liver and spleen when supply of iron is excess than body demand.
- Hemoglobin & Myoglobin required Fe for transport of O2 & CO2
- Cytochrome required iron for electron transport chain & oxidative Phosphorylation
- Fe associated for effective immunocompetence of our body
PHOSPHORUS
- Adult male person contained about 1kg of phosphorus and found in every cell of the body.
- Mostly combined with Ca to deposit in bone & teeth(80%).
- About 10% of body P is found in muscle & blood in association with protein, carbohydrate & lipid.
- Remaining 10% is widely distributed in various chemical compounds.
- SERUM PHOSPHORUS LEVEL
- In whole Blood- 40mg/dl
- Serum level- 3-4mg/dl
- Serum Phosphate
- Free Form 40%
- Complex form with Ca, Mg, Na, K ions is about 50%
- ABSORPTION
- Absorption mostly from Jejunum.
- Calcitriol increased absorption of P among with Ca.
- Acidity in intestinal lumen increased absorption of P.
- EXCRETION
- Urinary excretion about 500mg/day.
- Renal Threshold 2mg/dl.
- Reabsorption of phosphate by renal tubules is inhibited by PTH.
- BIOCHEMICAL FUNCTION
- Phosphorus is essential for development of Bone and teeth.
- It play a central role for formation & Utilization of high energy phosphate compound like ATP.
- Required for formation of Phospholipids, phosphoprotein, Nucleic acid.
- As phosphate buffer for maintenance of pH of blood (around 7.4) & cell.
MAGNESIUM
- Body contain about 20 gm of Mg. -70% presence in bone in combination of Ca & P. -30% in soft tissues & body fluids.
- DIATERY REQUIREMENT
- Adult Male= 350mg/day
- Adult Female= 300mg/day
- SERUM LEVEL
- NORMAL LEVEL= 2-3mg /dl
- Ionized form-60%
- Protein Bound-30%
- Combination with other ions-10%
- BIOCHEMICAL FUNCTION
- Required for formation of Bone & Teeth.
- Mg ion serve as cofactor for several enzymes requiring ATP like
*Hexokinase
*Glucokinase - For proper neuromuscular function, Low Mg level leads to neuromuscular irritability.
POTASSIUM
- Potassium is a principle intracellular cation.
- ABSORPTION
- 90% Absorption in GI Tract.
- Very little loss through feces, however a subject with diarrhea a good proportion of potassium lost in feces.
- BIOCHEMICAL FUNCTION
- Potassium maintain intracellular osmotic pressure.
- It is required for the regulation of acid base balance & water balance in the cell.
- Potassium is required for transmission of nerve impulse.
- Extra cellular K ions influence cardiac muscle activities.
- NORMAL VALUE IN SERUM- 3.5-5 mmol/L
MCQs
1.the normal value of serum potassium level is
a. 2.8-3.8 meq/L
b. 3.8-5 meq/L
c. 5-5.8 meq/L
d. 6-7.2 meq/L
Ans: B
2.Daily requirement of iron man is :
a. 1gm
b. 1o microgram
c. 10mg
d.5mg
Ans: C
