Английский язык - Страница 50

It is accepted that the total amount of iron in the body is between 2 and 5 g., varying with body-weight and hemoglobin level; about two-thirds of this is in the form of hemoglobin and about 30 % is storage iron; iron in myо-globin and enzymes makes up the small remaining fraction together with iron in transport, which is only 0,12 %. There is a big difference between the sexes: in the adult male the total iron is about 50 mg. per kg. body-weight. But in the adult female the figure is only 35 mg. per kg., mainly be cause the normal blood-level of hemoglobin is lower than in the male. Iron exists in the body mainly in two forms: firstly, as heme in hemoglobin, and cytоchrome concerned with the utilization of oxygen; and secondly, bound to a protein without heme formation, as storage and transport iron. Iron in the body has a very rapid turnover, since some 3 million red blood cells are broken down per second and the greater part of the iron released is returned to the bone marrow and re-formed into fresh hemoglobin; some 6,3 g. of hemoglobin containing 21 mg. of iron is handled this way every 24 hours.

The amount of iron in the body is regulated by control of absorption, since excretion is very small. The amount of iron absorbed from food differs with different foodstuffs, so the com position of the diet is important. Absorption can be increased in the normal Individual when the blood-hemoglobin is lower than normal and is the iron stores are low. Iron stores are normally lower in women than men and so they tend to absorb more iron. Iron absorption can decrease in older persons, especially in those over 60. Many estimates have agreed that the average Western diet pro vides between 10 and 15 mg. of iron daily, of which only 5 – 10 % is absorbed.

Iron absorption takes place mainly in the upper jejunum, though some is absorbed in all parts of the small intestine and even in the colon. Iron in food is mostly in ferric form and must bе reduced to the ferrous form before it can be absorbed; this reduction begins in the stomach – though very little is absorbed there – and continues in the small intestine. The iron is absorbed via the brush-border of the intestine and then may take one of two paths; it is either passed into the blood, where it combines with a globulin, and passes to the marrow or to storage sites; or it combines with the protein, which is then deposited in the intestinal cells.

Iron is lost mostly through the gastrointestinal tract by way of red cells and intestinal cells containing iron lost in the constant desquamation from the intestinal mucosa.

iron – железо

varying – изменение

hemoglobin – гемоглобин

storage – хранение

myоglobin – миоглобин

fraction – фракция

together – вместе

body-weight – масса тела

desquamation – десквамация