If we have look at the wall of the small intestine,
then it has some similarities to the wall of the stomach.
So it's got these muscular layers, it has
a circular and longitudinal muscle layers
which we can see here and also similar
to the stomach, its inner lining
is thrown into a series of elevations.
But importantly these transverse folds
do not disappear with distension.
So the rugae in the stomach allowed
the stomach to expand in
size as more food passed in.
These transverse folds
known as the plicae
are a permanent feature;
they're not lost with distension.
And their purpose is to increase the surface area.
Increase the surface area of the
small intestine allowing great
opportunity for absorption to occur.
Similar again now to the
stomach, we have mucus
the mucosa, sorry, the mucosa, which
contains these intestinal villi.
And these are covered
themselves with microvilli.
And these again increase the
surface area. So the small intestine
is long 6-7 meters long and due to this
plicae, these folds, and these microvilli
on top of intestinal villi,
we can see that we have a very large surface area.
You can see these intestinal villous here.
Also within the wall of the small
intestine, we have intestinal glands
and these are found on base of those
intestinal villi so we have intestinal glands;
we can see some here. These are
important. They contain goblet cells.
These produce mucin which
is mixed to form the mucus.
The lines, the internal surface of
the small intestine. Again important
if some hydrochloric acid was
to creep from the stomach into the
duodenum. And it also has
some stem cells. This is quite
attritional environment and the food
passing over can damage the cells
so we have stem cells for the
replenishment of the epithelial layer.
We also, and these are only found in the duodenum
have, what are known as the Brunner's glands.
These Brunner’s glands located in the
duodenum produce lots of alkaline mucus.
This is really important as
it helps to protect the duodenum
from any acid that's creeping
into the duodenum from the stomach.
It also helps to inhibit
the gastric acid production.
So once the food is passed from the stomach
into the duodenum, the duodenum is no longer
under attack from any acid creeping in.
So the wall structure is similar in
someways that to the stomach, but it's not
increasing in the surface area
which is lost with distension.
This increase in the surface area is
maintained to optimize absorption.