What is digestion?
Digestion is the breakdown of large
insoluble molecules into smaller
soluble molecules which can pass
through the wall of the gut into the
blood.
Wow, sounds complicated.
Really, it’s not. Let us tell you about it.
How does it start?
Well first you chew something with
your teeth. Which makes it have a
larger surface area, then and enzyme
in your saliva called amylase starts
breaking the carbohydrate into sugar.
Oh, I see, what happens then?
The food is then pushed down the
oesophagus to the stomach by
PERISTALSIS.
What is peristalsis?
Glad you asked that! Here I’ll explain
it to you.
Peristalsis is the contraction and
relaxation of the circular muscles in
the wall of the gut.
When the muscle relaxes
the food drops down and
when it contracts at the
top the food at the bottom is pushed
down
I see, what happens then?
The food is then in the stomach, the
food is churned around by more
waves of peristalsis to make it into
mush, and it mixes with gastric juice.
What on earth is that?
Gastric juice contains and enzyme
called protease which breaks down,
yup you guessed it, protein, into
amino acids.
It also contains hydrochloric acid
which kill bacteria and makes the
optimum PH for this enzyme, meaning
it will work at its best at a lower PH.
I think I got that.
The food is then released a little bit at a
time into the duodenum, which is the first
part of the small intestine.
Ok does it have an enzyme too?
The duodenum DOES NOT
produce any digestive juices,
but has 2 poured into it!
*Did you know the small intestine is 6m long?*
Whoa that’s really long!
One of the juices comes from the
pancreas. It contains carbohydrase,
protease and lipase.
I know the other two but what does
lipase do?
It breaks down lipids.
What are they?
They are fats and oils.
Where does the other digestive juice
come from?
The other digestive juice is call bile.
Which is made by the liver and stored
in a bag called the gall bladder. It is
NOT AN ENZYME, but it neutralises
the acid that was added in the
stomach. This helps the small
intestine work more effectively.
Bile also helps emulsify the fats.
What’s emulsify mean?
It means to make the fats into smaller
blobs to make their surface area
larger. So that the lipase can digest
quicker.
The food is now a semiliquid like a smoothie! And
it passes into the second part of the
small intestine called the ileum.
The walls of the ileum make a digestive
juice which contains
carbohydrase, protease
and lipase.
What does this do?
These enzymes complete the digestion of
fats to fatty acids, glycerol, (carbohydrate)
to simple sugars and protein to amino
acids.
Oh I see, what then?
The ileum is specially adapted for
absorption, passing digested food into the
blood. It is very long to allow time for
digestion
It has a very large surface area due to
the presence of villi (finger like
projections) and microvilli
This allows rapid diffusion
of the products of digestion.
Aren’t villi walls only one cell thick?
Yes, well done, this helps speed up
the diffusion.
Each Villus has a blood vessel and a
lymph vessel to carry the food away.
Is that all?
Not quite, all the food which cannot
be digested ends up in the large
intestine. It enters into the colon
where most of the water is
reabsorbed into the blood.
The indigestable remains form a semi
solid faeces which is stored in the
rectum. Eventually it is passed out
the anus.
So you might need one of these…
How much did you remember?
What enzyme is in saliva?
What does that help break down?
What type of food is broken down in
the stomach?
What happens to food that can’t be
digested?
What is the function of bile?
Well here’s what I got!
1)Amylase
2) That starts to break down carbohydrates
3) Proteins, by an enzyme called protease
4) It is passed out of the body through the anus
5) It neutralises the acid that was added in the
stomach. This helps the small intestine work
more effectively.
Well done 5/5!
So what do I get for 100%?
Sweeties! To do some of
your own digestion!
Take a look at this too!
http://www.medtropolis.com/VBody.asp
(right click and open hyperlink, click on English, digestive tract
and then guided tour!)