Welcome.
discussion of the gastrointestinal tract. This is the or I call it the GI tract,
this is the tract that enables us to bring nutrients, electrolytes and water
into the body. So we're moving it from our external
environment to the inside of the body and then into the bloodstream for delivery to
all the cells of the, of the. Of the body.
So how does this thing work. So the GI track is a tube, which is about
five meters in length. And this tube has an opening at the top
which is your mouth, and that's what's shown here.
So here's the mouth. And at the, and at the end of the tube,
we have the anus. And the tube is, is going to allow then
food materials to be coming into the mouth from your diet and these are going
to be complex foods such as steak and potatoes.
And we need to, to convert this steak and potatoes into simple molecules which can
be used by the cells of the body. for fuel.
So we want to be able to convert then the steak and the potatoes into amino acids
and into simple sugars. This is done by the gastrointestinal
tract and it sort of acts like a processing plant.
So the first thing that happens is that these complex food materials enter
through the mouth and as they enter into the mouth then we chew on them and break
them down into smaller. And smaller particles this increases the
surface area of the particle and allows then for attack by enzymes.
So what we're increasing the surface area and this material then is very rapidly
going to be transmitted from the oral cavity through the esophagus which is
essentially a tube down the to the stomach.
Once we reach the stomach. Once we're in the stomach then we're
going to start the process of digestion. And this is going to be converting the
complex, the complex materials such as a steak into polypeptides and then from
polypeptides into amino acids. Digestion is going to occur within the
stomach, but it's also going to occur within the next region which is called
the small intestine. And in the small intestine we will
further break down these particles to very simple molecules such as glucose and
amino acids. And then, we're going to absorb these
things these small molecules across the ephithelial cells, which are lining this
tube and enter into the body. Material that's left over is going to be
released from the anus as fecal material. So this is going to be the waste products
that cannot be used by the body. In a typical day you're taking in
something like a litre to two litres of solids as well as fluid in, in a given
meal and as it passes through the GI tract you will add about seven litres of
secretions. Which can be acids, it can be buffers and
it can be enzymes and as it moves through the small intestine then.
We could have as much as nine litres of fluid.
But this, most of this fluid is going to be reabsorbed as it's moving through the
small intestine, and so that we end up with fecal matter which is only about 200
to 500 millilitres. And the rest of the material then will be
reabsorbed as we're moving through the small intestine, and into the large
intestine. So that means that along this track,
we're going to have regions that are have specific functions.
And we're going to want to be moving our material in a unidirectional manner, so
we start at the mouth, and we're going to be moving towards the anus.
And this unidirectional manner is, is going to be due to smooth muscle
contraction which is, which is propelling the boldest of food.
And food stuffs through the tract. In addition to having the, the GI track
itself. The GI track proper we have an other
organs which are going to help in this process.
In this processing of food, of food. The first of this is the salivary gland.
The salivary gland secrets saliva which moistens the food particle as it coming
in through the mouths for chewing, and that allows the food particle to easily
slides down the esophagus to the stomach. The second is that we have the liver and
we have the pancreas, and these two these two organs are going to be secreting,
materials which are going to aid in the digestion of the foodstuffs within the GI
tract itself. And that's going to be predominantly,
within the small intestine. As we're moving down this track, we have
specific sphincters, which are gating the entry and exit from the track.
And these, the, at the top, we have a voluntary sphincter, which is for
swallowing. And at the bottom, we have a voluntary
sphincter. Which is, for avoiding the feaces, under
our control. So we have skeletal muscle that,
sphincters at the top and at the bottom of the tube.
There are also sphincters within different regions of this tube, which are
smooth muscle sphincters, there are under involuntary control.
And the smooth muscle sphincter, for instance, resides here.
As we're moving from the esophagus into the stomach.
And then from the stomach as we're moving from the stomach into the beginning of
the small intestine which is the duodenum.
And then again we have a involuntary sphincter as we're moving then from the
from one region of the colon to the, to the anus.
So the track, then, is going to be this movement of food materials along the
track. And as it's moving along the track, we're
going to be changing the actual structure of these materials and then, absorbing
the materials and so that, at the end, we have waste product which is not useful to
the body. And that will be what's, what's expelled
from the body. So let's look a little bit more at the
anatomy of the GI tract itself. So, I told you that the tube is a
muscular tube. On the outermost regions of the tube, we
have two layers of muscle, and that's what's diagrammed here.
The inner layer which is here. The inner most layer of this muscle is
called the muscularis externa is this, this muscle, this smooth muscle is
oriented circumferentially around the lumen.
So when it contracts then it's going to, to make the diameter of the tube smaller.
