Slide 10
How oral rehydration worksThis slide explains why some of the chemicals, in ORS are useful.
The two diagrams each show a piece of small bowel (or intestine). Find the shaded
lumen in the middle of the intestine, and imagine
that outside the intestine wall is the blood and body tissue. Fluids are
absorbed from the lumen through the wall into the blood. The straight arrows at
the bottom show the loss of fluid in a diarrhoea stool. Above these 'stool'
arrows are two curved arrows coming out of the intestine
wall. They show the increases secretion, or pouring out, of fluid into the intestine.
It is this increased secretion that causes the body to lose water and salt in
the stool. The salt is mainly sodium chloride, but also some potassium chloride.
It is the loss of water, or dehydration, and the loss of salts which are the
dangers of diarrhoea. Notice that all the arrows we have described so far are
the same size in both diagrams.
Now look at the top of the left hand diagram. The top arrow shows that we are
putting in salt and water, because that is what the body is losing with the
stool. Notice the small arrow going into the intestine wall, to show how much
salt and water it absorbs.
Now look at the top of the right hand diagram, and compare it with the left hand
one.
Q. What two differences can you see between the two diagrams?
Teacher's Note
Stop here and allow students to try to find the difference for themselves. |
A. First, the fluid going into the top of the right hand intestine contains glucose
in addition to salt. Second, on the right, the arrows
which show how much fluid the intestine absorbs are very much larger. These big
arrows show that the glucose makes
the intestine absorb much more salt and water. If there is no glucose, as on the
left, very little salt and water are absorbed. Most of the oral fluids just pass
on and make the stools larger.
When people first tried to give fluids by mouth, they did not understand about
how glucose help. They gave only salt and water so the treatment failed.
Q. What effect does the glucose have on increased secretion
of fluid into the intestine?
A. Glucose does not reduce the secretion of fluid. That is why the size of the
arrows for "Secretion" are the same in same in both diagrams. Glucose
only helps the absorption of water and salts to replace what is lost.
Q. So what effect does ORS solution have on the diarrhoea?
A. ORS solution docs not stop the diarrhoea. This may continue for some days.
But ORS solution reduces the danger of diarrhoea, because it replaces the
essential water and salts. So, although it seems so simple, ORS solution is a
scientifically appropriate drink. It is possible for you to make up and use such
a mixture in your own home.
Further Discussion
Potassium chloride is added to ORS because the body loses potassium as well
as sodium salts. Sodium bicarbonate is valuable to restore the acid-base
balance. In severe diarrhoea, the body becomes acidotic. We do not emphasise
these in the main text, because it is the "salt and sugar" combination
that is important and can be most easily improvised under village conditions.
Teacher's Note
Students who have had less than 4 years of secondary education may find bar
graphs difficult. In this case, we suggest that you omit="diarrhoea-management-11.htm" target="_blank"> Slide
11. The time can
be more usefully spent on the other slides. |
