• # question_answer 1) Explain the significance of sodium, potassium, magnesium and calcium in biological fluids.

BIOLOGICAL IMPORTANCE OF SODIUM AND POTASSIUM Both sodium and potassium ions are essential constituents of biological fluids. It is observed that a human being weighing about 70 kg contains about 90 g of Na and 170 g of K respectively. Though $N{{a}^{+}}$and ${{K}^{+}}$ions are quite similar chemically but they differ greatly in their biological activities. Their distribution in biological systems is also different. The ${{K}^{+}}$ions are present in higher concentrations inside the cells while $N{{a}^{+}}$ions are present in higher concentrations outside the cells. $N{{a}^{+}}$ions are primarily found in blood plasma and interstitial fluid which surrounds the cells. These ions participate in the transmission of nerve signals, in regulating the flow of water across cell membranes and in the transport of sugars and amino acids into cells. Potassium ions, which are abundant within cell fluids, activate many enzymes which are responsible for oxidation of glucose to produce ATP. There is considerable variation in the concentration of $N{{a}^{+}}$and ${{K}^{+}}$ions found on the opposite sides of cell membranes. The cation gradients control the development and the functioning of the nerve cells. These ionic gradients called the sodium-potassium pump operate across the cell membranes. The energy for this operation is provided by hydrolysis of energy rich molecules ATP. Thus, both sodium and potassium ions are essential ions for living organisms. The daily requirement of sodium and potassium is about 2 g each. BIOLOGICAL IMPORTANCE OF MAGNESIUM AND CALCIUM An adult body contains about 25 g of magnesium and 1200 g of calcium. $M{{g}^{2+}}$ions are concentrated in animal cells and $C{{a}^{2+}}$ions are concentrated in body fluids outside the cells in the same way as ${{K}^{+}}$ ions concentrate inside the cells and $N{{a}^{+}}$ ions outside the cells. Magnesium serves a variety of functions in metabolic processes and nerve action. All enzymes that utilize ATP in phosphate transfer require magnesium as the cofactor. The recommended daily intake of magnesium for adults is 350 mg. In plant life, magnesium plays a critical role in photosynthesis, the process by which plants convert carbon dioxide and water into sugars. The magnesium is present in the green pigment. Chlorophyll, which is necessary for capture of energy from sunlight. Solar energy is the energy source for the reactions of photosynthesis. Calcium is essential to all living matter. About 99% of it is in the bones and teeth, principally as the mineral hydroxyapatite,$C{{a}_{5}}{{(P{{O}_{4}})}_{3}}OH$. The other 1% is involved in several processes: clotting of blood, maintenance of a regular heartbeat, proper functioning of nerves and muscles and various aspects of metabolism. The calcium concentration in plasma is regulated at about$100mg\,{{L}^{-1}}$. It is maintained by two hormones: Calcitonin and parathyroid hormone. It is important to know that bone is not an inert and unchanging substance but is continuously being solubilised and re deposited to the extent of 400 mg per day in man. All this calcium passes through the plasma. Children require an adequate daily intake of calcium for the proper development of bones and teeth. Adults especially older women require calcium to prevent osteoporosis, a condition in which the bones become porous, brittle and are easily broken. The recommended daily intake of calcium for adults is 1200 mg.