The principal mineral elements that animals require are listed in Table 50.1. Elements required in large amounts are called macronutrients; elements required in only tiny amounts are called micronutrients. Some micronutrients are required in such minute amounts that deficiencies are never observed, but they are nevertheless essential elements.
Calcium is an example of a macronutrient. It is the fifth most abundant element in the body; a 70-kg person contains about 1.2 kg of calcium. Calcium phosphate is the principal structural material in bones and teeth. Muscle contraction, neuronal function, and many other intracellular functions in animals require calcium ions. The turnover of calcium in the extracellular fluid is high, as bones are constantly being remodeled and calcium is constantly entering and leaving cells. Calcium is lost from the body in urine, sweat, and feces, so it must be replaced regularly. Humans require about 800 to 1,000 mg of calcium per day in the diet.
Iron is an example of a micronutrient. Iron is found everywhere in the body because it is the oxygen-binding atom in hemoglobin and myoglobin and is a component of enzymes
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