Now that we have food into the stomach,
let’s first talk about the top
portion of the stomach that
relaxed to be able to
get the food into it.
So this is the lower esophageal
sphincter and the cardia.
This is where food enters into the stomach
and it’s also the place in which you can
regulate belching or releasing air.
The fundus or body of the stomach.
This acts mainly as
reservoir or holds food,
but it also houses some very unique cells
called interstitial cells of Cajal.
These are the pacemaker cells for
slow waves within the stomach.
The final areas of the stomach
are the lower portions
and this is the antrum, which is
the lower portion of the stomach,
and finally, the pylorus.
And the pylorus will have the sphincter
that will release or allow for
the release of stomach contents
into the small intestine in the upper
portion known as the duodenum.
But the antrum serves another
very important aspect.
It actually uses its contractions
to help mix and grind food
because remember you’re
releasing a lot of fluid,
you’re releasing hydrogen ions,
you’re releasing pepsin
and therefore, you need to mix all those
together before you can get complete
digestion of certain
aspects in the stomach.
To show this in a little bit more detail,
I can use this particular diagram.
Here, you can see one particular
contraction. In this case, contraction A.
As it contracts, it moves some food
stuff towards the pyloric sphincter.
But the other portion
is pushed backwards.
We put in a second contraction.
A little bit of it gets pushed forward
and even more gets pushed backwards.
And finally, a third contraction
does the same thing.
Some gets pushed forward
and some backwards.
This backwards and forwards contractions
allow for that mixing process to happen.
as you do that mixing,
a little bit usually gets pushed
through the pyloric sphincter
because there is enough
pressure to move past that.
So a little bit gets moved past into the small
intestine and the rest of it gets mixed.
As you continue contracting, you
continue that mixing movement.
Okay, now that we’ve reached
the topic of some of the
substance in the stomach moves
past the pyloric sphincter,
you might ask, “Well, what
regulates that process?
And how do we know what things can move
past the pyloric sphincter the fastest?"
To look at this, we can have a graph
where we’re graphing time on the X-axis
and on the Y-axis, it’s the
time remaining in the stomach.
Hopefully, you can see
from this kind of graph
that a liquid is emptied
faster than a solid food.
Also, something that has a high
amount of glucose is emptied
before something that has
higher amounts of protein.
And the reason why this is
an important process is
that certain foods will
stay in the stomach longer.
If it is sold and if it has a
high protein concentration,
those things will stay
in the stomach longer,
than if it is liquid and has a
high glucose concentration.
So we can digress this process about fats,
proteins, and carbohydrates in this format.
Carbohydrates are emptied first,
followed by proteins, and finally, fats.
Liquids are emptied faster than solids.
And if you have a high osmolality,
you will delay gastric emptying
And what do I mean by high osmolality?
That has a high sodium concentration
and that usually delays the amount
of gastric emptying that occurs.