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 intes ti-nal cells.

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

Fat factor

An enzyme abnormality has been discovered in the red blood cells of people who are overweight. It's the first clue that obe sity in humans may bе caused by a biochemical defect – not simply by overeating.

Researchers found that obese people have lower levels of a special enzyme that functions as a pump, transporting potassium and sodium in and out of cells. They suggest that with low levels of this pumping enzyme, less energy is used. Thus fewer calories are burned up as heat, while more are stored as fat.

New words

act – акт three – три

stage – стадия

first – начальный

voluntary control – добровольный контроль

soft – мягкий

mass – масса

mastication – перетирание

position – положение

root – корень

lingual muscles – языковые мускулы

second – секунда

brief – резюме

occupied – занятый

guiding – руководство

movements – движения

purely – просто

nature – природа

seized – захваченный

peristaltic – перистальтический

wave – волна

traveling – путешествие

along – вперед

before – прежде

cardiac sphincter – сердечный клапан

total – общее количество

amount – количество

iron – железо

varying – изменение

hemoglobin – гемоглобин

storage – хранение

myоglobin – миоглобин

fraction – фракция

together – вместе

body-weight – масса тела

Present Perfect Tense (действие, совершившееся в прошлом, связано с настоящим).

Спряжение глагола to write в Present Perfect Tense Таблица 13

Запомните типичные для Present Perfect обстоятельства: already, not yet, just, ever, never.

Сравните также:

I have bought a book today (this week, this month) – неистекший отрезок времени – Present Perfect.