Mineral Metabolism PDF

# Minerals ## Mineral Metabolism - Minerals are essential for the growth and maintenance of the body. - If the daily requirement is more than 100mg, they are called *Major elements* or *Macrominerals*. - If the requirement of certain minerals is less than 100mg/day, they are known as *Minor elemen...

# Minerals ## Mineral Metabolism - Minerals are essential for the growth and maintenance of the body. - If the daily requirement is more than 100mg, they are called *Major elements* or *Macrominerals*. - If the requirement of certain minerals is less than 100mg/day, they are known as *Minor elements* or *Microminerals*. - **Macrominerals** include calcium, magnesium, phosphorus, sodium, potassium, chloride, sulphur and fluoride. - **Trace elements** include iron, iodine, copper, manganese, zinc, molybdenum and selenium. - K⁺ and Cl^- Mg²⁺, PO₄^3- metabolism. ## Potassium (K⁺) - Total body potassium is about 3500 meg, out of which 75% is in the skeletal muscle. - Potassium is the major intracellular cation and maintains intracellular osmotic pressure. - About 98% of the total body K⁺ is in cells (150-160mEq/L), only 2% in the ECF (3.5-5mEq/L). - Transmission of nerve impulses, contraction of heart requires potassium. - During depolarization, there is sodium influx and potassium efflux reversed depolarization. - After the nerve transmission, these changes occur in the cell. - The recommended daily allowance per day is 2-5gm. - **Sources rich in K⁺ but low in Na⁺ are:** banana, orange, apple, pineapple, almond, dates, beans, jam and potatoe. - Tender coconut water is a very good source of K⁺. - Vegetables, white gram, meat, milk, legume can be good sources. - Plasma potassium level is 3.5-5mEq/L (same value as serum). ## Metabolic Functions of K⁺ - Nuclear activity and protein synthesis are dependent on K⁺. - It is required for the transmission of nerve impulses. - It influences activity of cardiac and skeletal muscle. - Several glycolytic enzymes need K⁺ for their formation. - It maintains the intracellular osmotic pressure, water balance and acid-base balance. - K⁺ is required for all action potentials for muscle contractions. ## Clinical Conditions Related to Plasma K⁺ Level Alterations: 1. **Hyperkalemia**: - Plasma K⁺ level above 5.5 mmol/L is known as hyperkalemia. - Since the normal level of K⁺ is kept at a very narrow margin, even minor increase is life-threatening. - In hyperkalemia, there is increased mental & muscle excitability, which leads to ventricular arrhythmia and ventricular fibrillation. - Hyperkalemia is characterized by flaccid paralysis, bradycardia and cardiac arrest. - **Symptoms:** - First manifestation is a decrease in heart rate below 60 beats per minute. - Changes in Electrocardiogram, Cardiac arrhythmia & muscle weakness. - It may be preceded by paresthesia (abnormal tingling sensation). - ECG shows elevated T wave. - **Causes:** - **Renal failure:** The kidney may not be able to excrete a K⁺ load when GFR is very low. - **Mineralocorticoid deficiency:** - e.g. in Addison's disease - Mineralocorticoid hormones that regulate sodium and potassium. - **Cell damage:** - e.g. trauma and malignancy - Increased hemolysis and tissue decay. - **Treatment:** - Give intravenous glucose and insulin. This produces glycogen synthesis. - When 1gm of glycogen is stored, 0.3mm of K⁺ is simultaneously trapped intracellularly. - So, the serum K⁺ is rapidly decreased. 2. **Hypokalemia**: - This denotes that plasma K⁺ level is below 3mmol/L. - **Symptoms:** include muscular weakness, cardiac arrhythmias and cardiac arrest, T wave may be flattened, U wave is inverted, confusion, lethargy. - **Treatment:** - It may be corrected by oral feeding of orange juice. - **Causes:** - **Gastrointestinal losses:** K⁺ may be lost from the gut due to vomiting, diarrhea. - **Renal losses:** Due to renal disease, administration of diuretics (diuretics cause K⁺ excretion, hence K⁺ supplemental is the standard treatment along with diuretics). - **Loop diuretics:** loss of 20% of K⁺ - **K⁺ sparing diuretics:** loss of 5% of K⁺ - **Hydrochlorothiazide:** withdraws water from the body and K⁺ along. ## Chloride (Cl^-) - Chloride is the major anion in the extracellular fluid space. - It is important in the formation of HCl in gastric juice. - Chloride ions are involved in Chloride shift. - Chloride concentration plasma is 96-106mEq/L. - **Sources include:** Table salt, leafy vegetables, eggs and milk. - RDA is 2-5gm. - It is rapidly and almost totally absorbed in the gastrointestinal tract. - Under normal conditions, chloride excretion occurs by way of three routes - the gastrointestinal tract, the skin and the urinary tract. Chloride is excreted mostly as NaCl and chiefly by way of the kidney. ## Functions - As a part of NaCl, chloride is essential for water balance, regulation of osmotic pressure and acid-base balance. - It is involved in chloride shift. - It is necessary for the formation of HCl by the gastric mucosa and for activation of enzyme amylase. ## Clinical Conditions Related to Plasma Chloride Level Alterations: 1. **Hyperchloremia:** - **(i) Cushing's syndrome:** Mineralocorticoids cause increased reabsorption from kidney tubules. - **(ii) Severe diarrhea** leads to loss of bicarbonate and compensatory retention of chloride. - **(iii) Renal tubular acidosis:** H₂CO₃ → H₂O + CO₂ → Na⁺ + HCO₃^- → Na⁺ + Cl^- 2. **Hypochloremia:** - **(i) Excessive vomiting:** HCl is lost so plasma Cl^- is lowered, there will be compensatory increase in plasma bicarbonate. This is called hypochloremic alkalosis - **(ii) Excessive sweating:** NaCl is lost - so plasma Cl^- is diminished, renal tubular reabsorption of Cl^- is decreased, and more Cl^- is excreted. ## Chloride Shift - Chloride shift is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO₃^-) and chloride (Cl^-) across the membrane of red blood cells. - Bicarbonate is exported from the RBC in exchange for chloride when the buffer effect of deoxygenated hemoglobin increases. ## Magnesium (Mg ²⁺) - Magnesium is mainly seen in intracellular fluid. Total body Mg²⁺ is about 25g, 60% of which is complexed with calcium in bone. - Magnesium orally produces diarrhea, but comparatively H-produces CMS. - Magnesium suppresses the activity of the brain and prevents abruption of the placenta. - RDA is 400mg/day for men and 300mg/day for women. Dose may be 600mg/day. More is required during pregnancy and lactation. - **Sources:** Cereals, pulses, nuts, green leafy vegetables, meat, eggs and milk. - Normal serum Mg²⁺ is 1.8-2.2mg/dL. ## Functions of Mg²⁺ - **(i) Mg²⁺ is an activator of many enzymes requiring ATP. It is needed in the phosphorylation cycle. ** - e.g., phosphofructokinase, adenyl cyclase - dependant kinase, etc. - Mg²⁺ influences the secretion of PTH by the parathyroid gland. - **(ii) Neuromuscular irritability is lowered by magnesium** - It is an important constituent of bone and teeth. - **(iii) Mg²⁺ supplementation improves glucose tolerance.** ## Excretions - It is excreted mainly by the way of intestine. All unabsorbed Mg²⁺ as well as that in biliary excretion and intestinal secretion are excreted through feces. - A fraction of absorbed magnesium is excreted by the kidneys through urine. ## Clinical Conditions When serum magnesium level falls below: - **1.8-2.1:** - Hypomagnesemia - **1.5-1.7:** - Oxygen of CHo (Tobraption and tremors) - **1.4-1.5:** - Liquor - **1.3-1.4:** - Liquor - **Convulsion is uncontrolled muscle contractions.**