GI Hormones – Gastrointestinal System

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.