00:00
Now, besides neural signalling
molecules, we also have hormones.
00:06
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.
00:15
The first is cholecystokinin and
these are released by I cells.
00:20
And these increase
enzymatic secretions,
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.
00:38
Gastroinhibitory peptide,
these cause the inhibition of acid secretion
as well as it also increases insulin.
00:48
And so sometimes this is called
glucose insulinotropic peptide.
00:52
Motilin is released by M cells.
00:54
And this increases contractions
of the various smooth muscle.
00:59
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.
01:13
And these migrating motor complexes help
really move food stuff along the GI tract.
01:19
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
signalling molecules.
01:37
These local signalling molecules are
called paracrine signalling molecules.
01:42
But before we do that,
let’s first talk through a
little bit about where the
GI hormones come from.
01:49
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.
01:59
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.
02:11
Glucose or gastric-inhibiting peptide is
released in the duodenum and jejunum.
02:18
Motilin is released in the
same locations from M cells.
02:22
Cholecystokinin is released
throughout the small intestine,
but tapers off in the ileum.
02:28
And finally, secretin follows
a very similar pattern
of being primarily released
in the duodenum, jejunum,
and then tapering in the ileum.
02:38
I promised you paracrine signalling
molecules and here they are.
02:42
Histamine is one of
the primary ones.
02:45
Histamine is released from ECL
cells as well as mast cells
and these increase acid secretion.
02:54
Nitric oxide is released by
many, many different molecules
and by cells in the system.
02:59
And mostly, this involves increasing both
blood flow as well as relaxing smooth muscle.
03:06
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.
03:19
Our final cell type of signalling
molecule that we have is somatostatin.
03:22
These are released by D cells and
this inhibits most secretions
and these are our four paracrine
signalling molecules.