Now, besides neural signalling
molecules, we also have hormones.
There are five primary hormones
And these we need to have identified because
as we go through the various GI lectures,
these will come up
over and over again.
The first is cholecystokinin and
these are released by I cells.
And these increase
contraction of the
gallbladder as well as
causing the pyloric
sphincter to constriction
Gastrin is released from G cells and
these causes increase in acid secretion.
these cause the inhibition of acid secretion
as well as it also increases insulin.
And so sometimes this is called
glucose insulinotropic peptide.
Motilin is released by M cells.
And this increases contractions
of the various smooth muscle.
It also does something called an
increase in this motility complex
that will help move food stuff from the
top of the GI system down to the bottom.
And these migrating motor complexes help
really move food stuff along the GI tract.
Secretin is released by S cells
and this increases bicarbonate
secretion as well as pepsin secretion
We have a few other items that we need
to deal with besides the GI hormones
and that is local
These local signalling molecules are
called paracrine signalling molecules.
But before we do that,
let’s first talk through a
little bit about where the
GI hormones come from.
I gave you all the cells
types that they come from,
but now let’s talk more in generality
about where anatomically they come from.
Gastrin is started off by some
release from those G cells
in the bottom portion of the stomach, the
duodenum, and it tapers off the jejunum.
Glucose or gastric-inhibiting peptide is
released in the duodenum and jejunum.
Motilin is released in the
same locations from M cells.
Cholecystokinin is released
throughout the small intestine,
but tapers off in the ileum.
And finally, secretin follows
a very similar pattern
of being primarily released
in the duodenum, jejunum,
and then tapering in the ileum.
I promised you paracrine signalling
molecules and here they are.
Histamine is one of
the primary ones.
Histamine is released from ECL
cells as well as mast cells
and these increase acid secretion.
Nitric oxide is released by
many, many different molecules
and by cells in the system.
And mostly, this involves increasing both
blood flow as well as relaxing smooth muscle.
Prostaglandins are also released
by many different cell types
and these increase both mucus
and bicarbonate secretion
as well it decreases the
secretion of hydrogen ions.
Our final cell type of signalling
molecule that we have is somatostatin.
These are released by D cells and
this inhibits most secretions
and these are our four paracrine