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الكيمـياء الحـيوية العامة Bioc211- Bioc101

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قديم 04-13-2008, 10:53 PM   #1
faridhalim20
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افتراضي mineral &water metabolism

MINERAL AND WATER METABOLISM
GENERAL CONSIDERATIONS
The mineral elements are essential components of the animal body. Their approximate relative amounts in the body are listed in Table.1
TABLE No.1
Mineral Element in the Human Body
Element Amount Element
(mg per kg body weight)
Oxygen 650
Carbon 180
Hydrogen 100
Nitrogen 30
Calcium 15
Phosphorus 10
Potassium 3.5
Sulphur 2.5
Sodium 1.5
Chlorine 1.5
Magnesium 0.5
Iron 0.04
Manganese 0.003
Copper 0.002
Iodine 0.004
Cobalt Very low amount
Fluorine Very low amount
Silicon Very low amount
Zinc Very low amount
With the exception of oxygen, carbon, hydrogen and nitrogen, the element calcium has the highest concentration and iodine the lowest. Various other elements are present in traces.
e.g., cobalt, fluorine, silicon and zinc these are sometimes called trace elements. Manganese, copper and iodine are sometimes regarded as trace elements. Traces of other elements, e.g., boron, arsenic, strontium, aluminium, bromine and nickel, have also been reported present but whether these are essential to the body structure has not yet been proved. These elements are widespread in food.
The sources of oxygen, carbon and hydrogen are the carbohydrates, fats, end proteins and oxygen of the air. Nitrogen and a considerable proportion of phosphorus and sulphur are spplied by proteins. The sulphur is provided in the form of cysteine, cystine and methionine. The phosphorus is also available in the form of the phosphoproteins, e.g., casein and vitellin. The remaining elements are supplied by the common salt (sodium chloride), by the mineral constituents of the natural foodstuffs and by the minerals of drinking water.
Inorganic substances or the mineral elements are present in tissues as ordinary salts or in complex combination with the living protoplasm. The major fraction of inorganic material is present in solution in body fluids and soft tissues, while in the bone it is deposited in the solid phase.
The diet must contain suitable amounts of minerals, in a total concentration of 4% of the dry weight of the food. This is essential for successful growth and maintenance of health. Growth is inhibited when the mineral contents of the diet falls below this level, or when it is raised to 16% the dry weight. Death results if the concentration of the mineral elements in the food reaches 32% of the dry weight.
(a) Functions of Minerals
Mineral elements aid in the regulation of the following body processes:-
1. The mineral elements enter into tne composition of every living cell, and so they determine the vital process of oxidation, secretion, development and reproduction. The inorganic elements function chiefly as catalysts in biological processes.
2. They influence the contractability of muscles e.g., calcium is necessary for the rhythmic activity of the heart muscles.
3. They are necessary for the irritability of nerves.
4. Mineral elements control osmotic pressure gradients in the body
and affect the movement of fluids in the body, e.g.; blood,
digestive fluids and urine
5. They activate the coagulation of blood, e.g., calcium is
important in this respect.
6. The pH of the blood is mainly controlled by the presence of these inorganic elements which constitute the main buffering. system of the blood, e.g., bicarbonates and phosphates.
7. Mineral elements are of importance in the digestive process, e.g., HCl formation in the gastric juice.
8. The iron-bearing haemoglobin plays an active role in the
transport of oxygen from the lungs to the tissues and CO2
tissues to the lungs.
9. Some elements are present as structural units of certain. hormones which profoundly influence the course of the metabolism. For example, iodine forms a constituent part of thyroxine, the hormone of the thyroid gland, which influences the energy metabolism of the body. In the absence of iodine (which is necessary for the proper functioning of the thyroid gland), maintenance of health in adult subjects and normal growth in the young are greatly impaired.
(b)Absorption, Storage and Excrection
The small intestine is the main organ for the absorption of inorganic compounds. The absorbed mineral elements are transported to the tissues by the blood and lymph. The skeleton is the main depot for calcium, magnesium, sodium, carbonate, phosphate and the trace minerals (aluminium, gold, lead, radium, silver, strontium, tin, zinc and fluoride). The muscle stores magnesium, potassium and sodium. The liver is capable of storing appreciable amounts of iron, copper, cobalt, manganese and nickel, The intestine is the major excretory organ for heavy metal ions, e.g., iron, copper, calcium and magnesium. The liver and large intestine also take part in the excretion of mineral elements. Inorganic substances, as potassium, sodium, chloride, fluoride, iodine and sulphate, are chiefly excreted by the kidneys.
Normally, small amounts of mineral elements are excreted in the sweat. The daily urine of an adult human subject contains, about 55 gm of total solids, 50% of which are inorganic salts.



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