Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Water and Mineral Metabolism Minerals are inorganic substances . Although they constitute a relatively small amount of the total body tissues , they are essential to many vital processes . Unlike vitamins , minerals are not destroyed in food preparation . But as they are soluble in water , some amount will be lost when cooking liquids are discarded . Unlike carbohydrates , fats and proteins , minerals do not provide energy . Seven principal (macro) minerals required by the body are sodium m potassium , calcium , magnesium , phosphorus , sulphur and chlorine . These constitute 60-80 per cent of all the inorganic material in the body . At least 7 other minerals are utilized in traces : ( microminerals ) iron , copper , iodine , manganese , cobalt , zinc and molybdenum . Minerals required for the body can be divided into 2 main groups – macrominerals which are required in amounts more than 100 mg per day and microminerals ( trace elements ) required less than 100 mg per day . Basic fuctions performed by the minerals are : 1. As structure components of body tissues 2. In the acid base balance 3. In the transport of gases 4. In muscle contractions SODIUM Sodium is the principal cation of the extracellular fluid . It is usually associated with chloride and bicarbonate in regulation of acid base equilibrium . Other functions are in the preservation of normal irritability of muscles , permeability of cells and in the maintenance of osmotic pressure of body fluid , thus protecting the body against excessive fluid loss . Daily requirement is 1-3.5 gm . About 95 % of the sodium which leaves the body is excreted in the urine as sodium chloride .Sodium is readily absorbed so that faeces contains very little except in diarrhea . Sodium is present in the blood mainly in the serum . Normal serum sodium level is 133-146m Eq / L. Hyponatremia Low levels of sodium in serum is called hyponatremia . It occurs in the following condition : 1. Excessive vomiting and diarrhoea resulting in excessive loss of fluid from gastrointestinal tract . 2. Severe burns 3. Acute Addison's disease 4. Chronic renal disease with acidosis 5. In active sweating and when take plain water . Hypematremia It is the increased level of serum sodium . This is not very common but may occur due to : 1. Hyperactivity of adrenal cortex as in Cushing's disease 2. Prolonged administration of cortisone , ACTH and sex hormones . POTASSIUM Potassium is the principal cation of the intracellular fluid . It is also a very important constituent of the extracellular fluid and influences muscles activity . Potassium ions are essential for contraction of cardiac and skeletal muscles . During muscular contraction , potassium from the muscle cells are lost into the ECF and after muscle contraction they are returned to the muscle cells . Potassium is essential for the activity of nerve cells and is present in the nerve fibres and maintains the proper transmission of nerve impulses . It maintains the electric potential of the cells as also their size . It influences the acid base balance and is also related to carbohydrate metabolism . The normal concentration of potassium in the serum is 3.5 – 5.5 m Eq / L . Vegtables are rich sources of potassium . The recommended amount of potassium for adults 4 gm / day Hyperkalaemia This is due to increased serum potassium and occurs in the following condition : 1. Renal failure 2. Advanced dehydration 3. Addison's disease 4. Shock 5. Intravenous administration of excess amount of potassium. This is due to low levels of serum potassium and occurs in case of : 1. Diarrhoea and vomiting 2. Metabolic alkalosis 3. Familial periodic paralysis 4. Overactivity of adrenal cortex ( Cushing's syndrome ) 5. Prolonged administration of diuretics because of excretion of potassium in the urine 6. During heart failure . CALCIUM Calcium forms the largest amount of minerals present in the body . Calcium accounts for 2 per cent of the body weight and is almost entirely distributed in the bones and teeth . Requirements Men and women after 18 years of age = 800 mg daily During second and third trimesters = 1.2 -1.3g daily of pregnancy Infants under 1 year = 400- 600 mg daily Children 1 to 18 years = 0.7- 1.4 g daily Sources Dietary sources of calcium include milk , cheese , egg yolk , beans , lentils , nuts , figs , cabbage , turnip , green , cauliflower and asparagus . Blood Calcium Calcium is present exclusively in the plasma , to the extent of 9 to 11 mg % . The calcium content of plasma during infancy and early childhood is slightly higher . In the plasma , calcium exists in two physiologically distinct fractions : 1. Diffusible or ionized fraction 2. Non- diffusible or unionized fraction . A small fraction of about 0.5 mg% is present bound as an unionized complex ion with citrate. Absorption of Calcium 1.On a high protein diet 15 per cent of dietary calcium is absorbed. On a low protein diet, 50 per cent of the dietary calcium is absorbed. Phytic acid in cereal grains interferes with calcium absorption by forming insoluble calcium phytate in the intestine. So also the oxalates in food. 2.Calcium salts are more soluble in acidic media than in the alkaline media. 3.When fat absorption is not proper, much free fatty acids is present. These free fatty acids react, with free calcium to form insoluble calcium soaps. 4.If the Ca: P ratio is high, much Ca3(PO4)2 will be formed and absorption diminished. 5.Vitamin D promotes the absorption of calcium from the intestine. Functions 1.Calcium along with phosphorus is essential for bones and teeth formation. 2.For coagulation of blood. Calcium activates the conversion of prothrombin to thrombin. 3.For clotting and digestion of milk. 4.In muscle contraction. 5.In the normal transmission of nerve impulses. A low calcium level is associated with increase neuromuscular irritability. 6.Calcium ions are necessary for the maintenances and regulation of acid-base balance and water balance in the body. 7.Calcium and phosphate ions activate certain enzymes in the intermediary metabolism of carbohydrates, fat and proteins. Diseases Associated with Calcium Metabolism Rickets Deficiency of vitamin D in children causes impairment of intestinal absorption of calcium and phosphorus and produces rickets which is characterised by defective calcification. The bones therefore remain soft and deformed by body weight. Osteoporosis It is a condition when calcium is withdrawn from the bones. The bones become weak and porus and hence break. Excretion Calcium is excreted in the faeces, urine and sweat. About 200 mg of calcium, i.e about ¼ of to total excretion is excreted in the urine in 24 hours. PHOSPHORUS Phosphorus is present in every cell of the body. As inorganic combination with calcium Ca3(Po4)2, 80 per cent of the total is present in the bones and teeth. As organic phosphorus, it is present along with proteins as phosphoproteins and nucleoproteins. It is present along with carbohydrates as hexose and triose phosphates and along with lipids as phospholipids. Distribution The total amount of phosphorus in the body is about 700 gm. More than 85 per cent is found in bones, 15 per cent in soft tissues and 1 per cent in ECF, about 5 gm in brain and 2 gm in blood. In blood, phosphorus is present in the erythrocytes and plasma in two forms: (i) inorganic phosphorus and (ii) Organic phosphorus. Food Sources Food rich in phosphorus are cheese, milk, nuts, organ meat, egg, fish, cereals and vegetables. About 1.5 gm of phosphate is required to be taken in the diet. Functions 1.Phosphorus along with calcium is essential for bones and teeth. 2.For the formation of high energy bond compounds like ATP, ADP and creatinine phosphate. These are required for phos-phorylation of sugars in carbohydrate metabolism. 3.As a constituent of phosphate buffers in the blood and urine for acid-base balance. 4.For the formation of phospholipids, co-enzymes and enzymes of intermediary metabolism. 5.Constituent of phospholipids, nucleotides, nucleic acids, lipo-proteins and phosphoproteins. Clinical Importance Rickets and osteomalacia are important dietary deficiency disordes of calcium, phosphorus or Vitamin D. WATER Water forms 60 to 70 per cent of the body weight and is distributed throughout the body, being closely associated with the distribution of electrolytes in the body. It is present in the body both inside and outside the cells. There are two water compartments in the body: 1.Intracellular water (water present inside the cell) 2.Extracellular water(water present outside the cell). Extracellular water is further subdivided into: a. Plasma b. Interstitial fluid c. Dense connective tissue, i.e water content in the bones and cartilages d. Transcellular fluids. Functions 1. It acts as a carrier of nutritive elements to tissues and removes water materials from tissues. 2. It provides the media in which chemical reactions of the body take place. 3. The fluidity of blood is because of water. 4. It is a solvent for electrolytes and regulates the electrolytic balance of the body. It maintains the equilibrium of osmotic pressure extended by the solutes dissolved in water. 5. It is a regulator of body temperature. Because of its high specific heat, it can absorb or give off heat without any appreciable change in temperature. Also because of its high latent heat, it provides the mechanism for the regulation of heat loss by sensi-ble or insensible perspiration. Water Balance Water balance is maintained by a body when water gained by the body is equal to the water lost from the body. Water intake in gm per day Water intake as such = 1100 Water intake in diet = 900 Water produced during metabolism = 200 Total intake 2200 Water output in gm per day Water excreted in urine = 1000 Water excreted in stools = 200 Water lost through skin and lungs = 1000 Total output 2200 Dehydration Dehydration occurs when the fluid loss from the body is abnormally high, e.g. excessive perspiration in hot weather, severe diarrhoea, fever, vomiting, severe burns and in uncontrolled diabetes with frequent urination. In dehydration, besides changes in water balance, there will be also changes in electrolytes. Dehydration is corrected by electrolytes and water. Distribution of Electrolytes The body has two main fluid compartments of different electrolyte composition, i.e. the intracellular compartment where potassium (K+) is the predominant cation, and the extracellular compartment where sodium (Na+) is the predominant cation. The extracelluar fluid (ECF) can be subdivided into interstitial fluid where the protein concentration is very low and plasma (intravascular fluid) rich in protein. Distribution of electrolytes between plasma and interstitial fluid is given below. Electrolyte composition of ECF expressed in mEq wt/L. Cations Na+ K+ Ca+ Mg++ Anions HCO4 CI HPO4 SO4 Organic acids Proteins Intravascular Interstitial (plasma) fluid 142 138 5 5 5 5 3 3 155 151 27 103 2 1 6 16 155 32 108 2 1 6 2 151 Intracellular fluid 10 158 2 35 205 8 2 140 ____ ____ 55 205 Thus the predominant cation of ECF is Na+. The high concentration of Na+ in the plasma and the relative impermeability of Na+ ions across the cell wall membrane are important factors in controlling the distribution of water throughout the body and maintaining fluid balance. The concentration of Na+ in the plasma is controlled by the nerve receptors in the hypothalamus . An increase in the serum Na+ concentration will stimulate retention of water, thus diluting the serum balance to its normal level . A drop in the concentration of Na+ in the serum will initiate a loss of fluid from the body so plasma control the retention or loss of water from the body .