Hello! Today we’re going to
talk about upper GI secretions.
For this particular lecture, we have a
number of learning goals to obtain.
The first one is we will
learn the constituents
and the mechanisms of
and how salivary glands are
controlled and regulated.
Also, we will learn the
constituents of gastric secretions.
Finally, we’ll be able to
understand the mechanisms
of hydrogen ion secretion
from parietal cell,
as well as the control and
regulation of those parietal cells.
We will emphasize how this knowledge
then is applied to pharmacology
as we approach the task to
reduce gastric acid secretion.
So let’s get right into it.
The first thing that we’re
going to talk about
is some of the functions
of the GI system,
and this helps us to regulate
not only our functions now,
but integrate that into
what we’ve already covered.
We’re going to focus on the
upper portion of the GI tract.
Particular here, we’re going
to talk about the mouth,
the salivary glands which will
hydrolyze and lubricate food stuff.
And then finally, the stomach
which will act as a blender.
But here, what will be more important
will be the secretion of acid
to sterilize the food stuff.
Again, we have the mouth, the salivary
glands, and the stomach to talk about.
So, salivary secretions.
Why do we have salivary secretions?
One of the first most important aspects
is it helps protect the oral cavity.
So oral cavity protection is very important
and we’ll go through which items
do that in the constituents.
It also helps to lubricate food,
helps in the digestion of food,
especially carbohydrates and fats.
And what are salivary secretions
and where do they come from?
Well, the first thing that we need to
think about is the parotid gland.
And this parotid gland secretes
primarily serous secretions.
Serous secretion are
The sublingual and the
have a mixture of mucous
and serous secretions.
So altogether, the parotid gland
provides mostly serous secretion.
The sublingual and submandibular have a
mixture of serous and mucous secretions.
So, the serous secretions
will help with
hydrolyzing or getting
water into the food stuff,
and the mucous will
provide the lubrication.
What other constituents are
in the salivary glands?
Well, probably, we should start
off with talking about the ions.
There is a large amount of
potassium in salivary secretions,
and this primary function is so that
you can reabsorb sodium and water,
so you don’t lose as
much salt and water.
You also have bicarb ions which help
buffer hydrogen ions, or having a low PH.
You have two enzymes.
One is salivary amylase which
aids in starch digestion,
and lingual lipase which
aids in lipid digestion.
The reason why I state
that this aid in digestion
is if the salivary
glands are removed
and you don’t produce salivary
amylase or a lingual lipase,
you won’t lose the ability to
digest carbohydrates and fats.
It just won’t happen in the mouth.
They’ll only happen in
the small intestine.
You also have some items that help
do the oral cavity protection,
such as muramidase which is a lysozyme.
You have lactoferrin which helps bind
iron, and this prevents bacterial growth.
And you have some immune
mediator such as IgA
that are also released in the
salivary gland secretions.
Now, the ions that are released with
salivary secretions are released in a rate,
depending upon how much
salivary secretions there are.
So this can be diagrammed
in this kind of format,
where we have flow
rate on the X axis
and we have the concentration
of the ion on the Y axis.
You have salivary secretions
increasing the amount of sodium
that is released in the
salivary gland secretions,
and then we compare it
to the plasma value.
If it is below the level of the plasma
value, you are reabsorbing that ion.
If it is above the level of the ion
in the plasma, you are secreting it.
So in this case, you can see across flow
rate, you’re always reabsorbing sodium.
But you do a better job
at reabsorbing sodium
at a lower flow rate
than a higher flow rate.
Potassium, you secrete
because the potassium amount
in the blue line is above the
plasma value in the blue bar.
Finally, chloride is reabsorbed, and this
is done in a flow rate dependent fashion.
So, at low flow rates, you reabsorb more
chloride than at fast flow rates.
And finally, we have
bicarb which you secrete.
Again, you’re secreting it so
you can help buffer acids,
and you know it’s a secreted ion because
it’s above the level of the plasma.
So you have to do something
to make sure that happens.
So looking at all these
ions, I talked a lot about
how you either secrete
them or reabsorb them.
But how in the world you
go about doing that?
We need to talk